wind uplift behavior of wood roof sheathing panels ... · wind uplift behavior of wood roof...

Final Report:

Wind Uplift Behavior of Wood Roof Sheathing Panels Retrofitted with Spray-applied Polyurethane Foam ______________________________________________ Submitted to: Richard S. Duncan, Ph.D., P.E. Senior Marketing Manager, Spray Foam Insulation Honeywell Specialty Materials Fluorine Products 101 Columbia Road Morristown, New Jersey 07962

Jinhuang Wu, Ph.D. Technical Associate Huntsman 2190 Executive Hills Blvd. Auburn Hills, Michigan 48326

Prepared by: David O. Prevatt, Ph.D. Principal Investigator Assistant Professor (Structures Group)

Report No. 03-07 31 August 2007

______________________________________________________________________ Department of Civil and Coastal Engineering University of Florida 365 Weil Hall P.O. Box 116580 Gainesville, FL 32611-6580 ______________________________________________________________________

FOREWORD

The material presented in this research report has been prepared in accordance with recognized engineering principles. This report should not be used without first securing competent advice with respect to its suitability for any given application. The publication of the material contained herein does not represent or warrant on the part of the University of Florida or any other person named herein, that this information is suitable for any general or particular use or promises freedom from infringement of any patent or patents. Anyone making use of this information assumes all liability for such use.

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SUMMARY This report presents the findings of a research program sponsored jointly by Honeywell Specialty Materials (Honeywell) and Huntsman to identify structural benefits of spray-applied polyurethane foam (SPF) in the mitigation of hurricane damage to residential structures. The work was conducted at the University of Florida (UF) under the direction of Principal Investigator, Dr. David O. Prevatt, assisted by civil engineering graduate and undergraduate students and technicians. The project had three main goals:

1. To investigate the wind uplift behavior of wood roof sheathing connections retrofitted with Spray-applied polyurethane foam;

2. To demonstrate by structural calculations the potential structural benefit (if any) of SPF retrofit in roof truss-to-wall connections, and;

3. To review existing literature on the performance of unvented (sealed) attics and racking strength of SPF-retrofitted panels.

UF conducted static wind uplift tests on ½ in. thick by 4 ft by 8 ft oriented strand board (OSB) sheathing that were nailed to 2 in. by 4 in. southern yellow pine (SYP) wood members spaced 2 ft apart. Approximately one third of the panels were retrofitted by an SPF installer who applied 3 in. thick layers of closed cell spray-applied polyurethane foam (ccSPF) and another third had ccSPF fillets installed along the joints between the wood members and the ccSPF sheathing. The final final (control) set of panels were conventionally constructed using either 6d common or 8d ring shank nails. Tests were conducted at UF’s East Campus laboratory using a steel pressure chamber and vacuum pump following a modified ASTM E330 test procedure. The suction pressure on the exterior surface of the OSB sheathing was increased in stages until failure occurred. The ultimate failure capacities of the retrofitted panels were recorded and compared with the failure capacities of the non-retrofitted (control) panels. A total of 49 panels were tested. The mean failure pressure of the control panels was 77 psf, and the full layer ccSPF retrofit increased the mean panel failure pressures by almost 3.1 times, and the panels retrofitted with ccSPF fillets increased by 2.1 times. These controlled experimental results indicate that ccSPF retrofit has potential to improve the wind uplift performance of roof sheathing in wood-framed construction. Additional considerations such as, effect of trapped water between OSB and ccSPF, aged performance of the ccSPF, observed cupping of OSB sheathing, the effect of increased roof shingle temperatures and performance of field retrofitted ccSPF panels still need to be addressed in order to answer several concerns about the suitability of using ccSPF as a retrofit approach in hurricane-damage mitigation. The literature review revealed several recommendations of using ccSPF in the construction of unvented attics. Researchers suggest that unvented attics may be suitable for construction in the hot, humid climate zones (e.g. the south-east United States). While vented attics were recommended as having improved resistance to wind uplift during hurricanes, no scientific test data was found to support these conclusions. KEYWORDS: SPF; Polyurethane; Foam; Wind uplift; Sheathing; Roof; Retrofit, ASTM, Experimental Testing.

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TABLE OF CONTENTS

FOREWORD..................................................................................................................... II SUMMARY....................................................................................................................... III 1. INTRODUCTION.......................................................................................................1

1.1 BACKGROUND.................................................................................................................1 2. LITERATURE REVIEW ............................................................................................2

2.1 USING SPF TO IMPROVE IN-PLANE RACKING STRENGTH OF WOOD-FRAMED WALLS..........3 2.1.1 Discussion of NAHB Results ...........................................................................6

2.2 USING ADHESIVES AS A RETROFIT MEASURE FOR ROOFS IN HIGH WIND AREAS ................7 2.2.1 Retrofit Structural Adhesive of Sheathing-to-Wood Member Connection.......8 2.2.2 Retrofitting Roof Truss-to-Wall Plate Connections..........................................9 2.2.3 Discussion of Roof Truss-to-Wall Plate Retrofits ..........................................11

3. EXPERIMENTAL INVESTIGATION OF CCSPF RETROFITTED PANELS ..........12 3.1 RESEARCH OBJECTIVES................................................................................................12

4. MATERIALS AND METHODS................................................................................12 4.1 TEST CHAMBER ............................................................................................................13 4.2 ROOF SHEATHING PANEL CONSTRUCTION .....................................................................14 4.3 CCSPF APPLICATION ....................................................................................................16 4.4 TEST PROCEDURE ........................................................................................................18

5. RESULTS AND OBSERVATIONS .........................................................................20 5.1 FAILURE MODES FOR CCSPF RETROFITTED ROOF PANELS ............................................20 5.2 PHASE 1 TESTING.........................................................................................................22 5.3 PHASE 2 TESTING.........................................................................................................25

6. DATA ANALYSIS ...................................................................................................32 7. DISCUSSION OF RESULTS ..................................................................................36

7.1 NAIL PULLOUT ..............................................................................................................36 7.2 CCSPF FOAM RETROFIT ...............................................................................................38

7.2.1 Configuration B – Foam Fillet ........................................................................38 7.2.2 Configuration C – Full Foam .........................................................................39

7.3 PANEL STIFFNESS.........................................................................................................41 8. DESIGN WIND UPLIFT LOADS ACCORDING TO ASCE 7-05.............................42

8.1 ROOF SHEATHING WIND UPLIFT DESIGN LOADS.............................................................42 8.2 ROOF-TO-WALL CONNECTION WIND DESIGN UPLIFT LOADS ...........................................44

9. CONCLUSIONS......................................................................................................45 10. FUTURE WORK .....................................................................................................46 REFERENCES................................................................................................................48 LITERATURE REVIEW OF SEALED AND VENTED ATTICS ......................................50 APPENDIX A – DAILY TESTING REPORTS FROM SPF ROOF PANEL TESTING....57 APPENDIX B – INSULSTAR® BROCHURE .................................................................66

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LIST OF FIGURES Figure 2.1 – Roof-to-Wall Connection Retrofit Methods Using Adhesives (from Jones 1998) ...............................................................................................................................10

Figure 4.1 – Suction Chamber Pump and Controls (Pump #2).......................................14

Figure 4.2 – Test Specimen Layout and Nail Schedule ..................................................15

Figure 4.3 – Application of Second Lift of ccSPF for the Full Foam Specimens .............16

Figure 4.4 – ccSPF Application: (a) Configuration B – Foam Fillet, (b) Configuration C – Full Foam ........................................................................................................................17

Figure 4.5 – ccSPF Foam Fillets: (a) Phase 1 Fillet and (b) Phase 2 Fillet.....................18

Figure 4.6 – Suction Chamber with Roof Panel and Plastic ...........................................20

Figure 5.1 – Adhesive Failure Modes (from http://wikipedia.org) ....................................21

Figure 5.2 – Typical Failure Mode of No Foam Specimens using 8d Ringshank Nails...24

Figure 5.3 – Typical Failure Mode of Foam Fillet Specimens (Phase 1).........................24

Figure 5.4 – Typical Failure Modes for Configuration B on Phase 2 Testing ..................26

Figure 5.5 – First Failure Mode of Configuration C (Phase 2).........................................28

Figure 5.6 – Foam Residue Levels on Wood Members at Failure for Configuration C (Phase 2).........................................................................................................................28

Figure 5.7 – Second Failure Mode of Configuration C (Phase 2) ...................................28

Figure 5.8 – Third Failure Mode of Configuration C (Phase 2) .......................................29

Figure 5.9 – Fourth Failure Mode of Configuration C (Phase 2) .....................................29

Figure 5.10 – Wood Member Initially Twisted on Test Specimen #9 ..............................30

Figure 5.11 – Failure of Wood Member Initially Twisted on Test Specimen #9 ..............31

Figure 6.1 – Comparative Boxplot of Configuration B Showing the Difference in the Fillet Application.......................................................................................................................33

Figure 6.2 – Boxplot of Configuration C Test Specimen Groupings................................34

Figure 6.3 –Boxplots of Failure Pressure of the Combined Data for All Panel Configurations .................................................................................................................35

Figure 7.1 – Comparing Mean Failure Pressure and “Nail” Failure Mode (Tick marks show the 95% confidence intervals for the mean failure load) ........................................38

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Figure 8.1 – Components and Cladding Roof Zones for 7º ≤ Θ ≤ 27º and h ≤ 60 ft (excerpted from ASCE 2006 Figure 6-11C) ....................................................................43

Figure 8.2 – MWFRS Loading Patterns from ASCE 7-05 (ASCE 2006) .........................44

Figure A.1 – Vented and Unvented (Sealed) Attic Concepts (from Hendron et al. 2004)........................................................................................................................................51

Figure A.2 – Traditional U.S. Climate Zone Regions for Energy-Efficient Building Design (2002)..............................................................................................................................53

Figure A.3 – Map of DOE’s Proposed Climate Zones (Briggs et al. 2002) .....................54

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LIST OF TABLES Table 2.1 – Average Racking Load (lbs) of Each Wall Panel Configuration (excerpted from NAHB 1992)..............................................................................................................4

Table 2.2 – Maximum Racking Load of Wall Panels (lbs) (NAHB 1996) ..........................6

Table 2.3 – Summary Results of Using Adhesive as a Retrofit for Roof-to-Wall Connections (Jones 1998) ..............................................................................................10

Table 4.1 – Pertinent Pump Specifications .....................................................................13

Table 4.2 – Properties of Nails Used in Test Panel Specimens......................................15

Table 4.3 – Test Specimen Configurations .....................................................................17

Table 5.1 – Ultimate Failure Pressures of Test Specimens (Phase 1)............................22

Table 5.2 – Phase 2 ccSPF Uplift Testing Conducted July 2007....................................25

Table 5.3 – Phase 1 Configuration C Specimens Tested July 19-20, 2007....................31

Table 6.1 – Combined Data Summary Statistics for All Panel Configurations ................35

Table 8.1 – ASCE 7-05 Design Wind Pressures for Roof Sheathing Uplift* (psf) ...........43

Table 8.2 – Maximum Design Uplift Force for Roof-to-Wall Connections Using MWFRS*........................................................................................................................................44

Table A.1 – Global Advantages and Disadvantages of Vented and Unvented Attics .....52

Table A.2 – Climate Zone Definitions (2002) ..................................................................54

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1. INTRODUCTION

This report details methods, results, and conclusions of engineering investigations to

investigate the use of closed-cell Spray-applied Polyurethane Foam (ccSPF) in structural

retrofit applications of residential construction in high-wind areas. The research

consisted of three primary phases:

(1) Wind uplift tests of wood framed roofing panels representative of typical pre-2000

residential building construction and similar panels retrofitted with ccSPF;

(2) Design wind load analysis to determine the wind uplift capacity of a roof truss-to-

wall connections retrofitted with ccSPF;

(3) Literature reviews of sealed versus vented attics in residential construction and

the racking strength potential of ccSPF-retrofitted wall panels.

The main deliverable from this research is this report documenting the test methods,

results and findings on the use of ccSPF in structural retrofits of residential construction.

1.1 Background

Spray-applied Polyurethane Foam (SPF) is a foam product originally developed for use

as an insulating material in building (exterior wall and roof) construction. SPF can be

spray-applied to the undersides of roof decks and to wall cavities to act as a thermal

break between the exterior environment and the temperature controlled interior spaces.

SPF has been used in two formulations, namely “open-cell” and “closed-cell” foams. A

typical open-cell SPF (ocSPF) has a density of approximately 0.5 pcf, and it is used

mainly in filling cavities inside a building. During installation, the chemical undergoes

significant volumetric expansion (increasing by about 120 times its liquid volume) making

ccSPF Test Report 2 31 August 2007

it ideal as spray-applied insulation for use within wood-framed cavities. Open-cell SPF

has an R-value of about 3.6 per inch.

Closed-cell SPF (ccSPF) on the other hand, undergoes far less expansion (only

increasing by 30 times its liquid volume), and it was developed specifically for its high

thermal insulating properties (typical closed-cell SPF has an aged R-value of 6.2 per

inch). Closed-cell SPF is used as exterior roofing insulation for low-sloped roofs (once it

is protected from ultra-violet light that rapidly degrades the product). Closed-cell SPF is

manufactured with a density of 1.7 to more than 3.0 pcf and previous experiments have

shown that ccSPF rapidly develops high and tenacious bond (25-40 psi) to many

construction materials. Throughout this report, the term spray polyurethane foam or

ccSPF will imply closed-cell spray polyurethane foam.

Despite the measured strength and stiffness of closed-cell SPF, it has not been used as

a structural building material in the United States and there are no available design

guidelines relating to its structural properties. Experimental studies and analysis are

needed to understand the structural behavior of ccSPF products. Because of the

method of ccSPF application (spray-applied), it was felt that a potential structural usage

for ccSPF may be as a structural adhesive retrofit for existing residential houses.

2. LITERATURE REVIEW

The literature reviewed is on the use of ccSPF in building components and on the

subject of structural adhesives used in construction. Appendix C contains a literature

review of sealed versus vented attics in residential construction.


2.1 Using SPF to Improve In-Plane Racking Strength of Wood-framed Walls

Experimental studies (NAHB 1992; NAHB 1996) investigated using the structural

properties of SPF to improve the in-plane racking strength of wood-framed and light

gauge steel-framed shear walls. The National Association of Home Builders (NAHB)

conducted tests sponsored by the Society of the Plastics Industry, Inc. (SPI)

Polyurethane Foam Contractors Division. The focus of these experiments were to

determine if SPF can provide racking resistance against wind loads instead of using

traditional bracing techniques, i.e. panel or diagonal bracing.

A brief summary of the test method is provided here (excerpted from NAHB 1992).

Thirty (30) panels measuring 8 ft by 8 ft panels were constructed using 2 in. x 4 in. wood

studs and clad on one side using ½ in. thick by 4 ft by 8 ft gypsum drywall sheets

fastened to the framing. The horizontal joint between drywall sheets was taped and

finished with drywall compound. The other side of the wall framing was clad with one of

three different materials:

1. vinyl-clad panels,

2. 5/8-in. thick T 1-11 plywood siding panels, and

3. “conventionally clad” panels

Conventionally clad panels consist of drywall sheet on one side and on the other, a ½-in.

thick full plywood sheet (placed vertically) adjacent to a ½ in. by 4 ft by 8 ft fiberboard

sheet nailed to the framing members. This sheathing is covered with either the vinyl

siding or the T 1-11 siding. The “conventional cladding” simulates the plywood corner

shear bracing that is common in residential construction and the fiberboard sheathing is

a non-structural sheathing used on the remainder of the structure.


Racking tests were performed according to ASTM Standard E72, “Standard Methods of

Conducting Strength Tests of Panels for Building Construction,” Section 14 , which

evaluates the racking load of sheathing materials on a standard wood frame (8 ft by 8 ft).

Following this procedure, each wall panel has a 3.5 in. by 3.5 in. timber bolted through

the top plates and the racking load is applied to one end of this timber. The wall panel is

braced so that the wall only deflects in the plane of the load.

For each configuration, three wall samples were built and tested and the mean ultimate

failure loads are shown in Table 2.1. Tests were conducted on three (3) wall panels for

each configuration. Note that in the SPF-retrofitted panels, panels made with four wood

stud spacings (16 in., 24 in., 32 in., and 48 in. on center) were tested. The density of the

SPF used was 1.5 pcf.

Table 2.1 – Average Racking Load (lbs) of Each Wall Panel Configuration (excerpted from NAHB 1992)

SPF Panels Non-SPF Panels Stud Spacing

Vinyl T 1-11 Vinyl T 1-11

16” 2,800 5,300 913 2,890

24” 2,420 6,387 -- --

32” 2,588 -- -- --

48” 2,298 -- -- --

16” Conventional -- -- 3,853 5,262

From the results, the NAHB study found that SPF retrofits significantly increased the

ultimate racking strength of the vinyl-clad and T-1-11 clad wall panels. In addition, the

racking resistance of SPF-retrofitted panels constructed with vinyl siding varied from

60% to 72% of the ultimate racking strength of the “conventionally clad” wall panels.


Improvement was also observed in racking strength of the SPF-retrofitted T1-11 wall

panels with 16 in. and 24 in. stud spacing, with ultimate racking strengths respectively

equaled and exceeded (21%) the performance of the conventionally-clad un-retrofitted

wall panel.

The variation in stud spacing with SPF-filled wall cavities does not appear to be a major

factor in the racking strength. Since the racking strength is within 25% of each other for

all SPF filled wall specimens regardless of stud spacing, it seems as if the composite

action between only the SPF and the studs is not a major factor in developing the

racking strength. Instead, the composite action of the SPF and sheathing and/or the

effects of the individual components such as the sheathing and drywall and their

fasteners are resisting the racking load.

In 1996, the NAHB conducted racking strength tests on light-gauge steel framed walls

insulated with conventional batt insulation and with SPF (NAHB 1996). The average

density of the SPF used was 2.26 pcf. Only one test was conducted for each of the four

wall configurations listed below, following the ASTM E72 test protocol:

1. 7/16” OSB (front side) and ½” drywall (back side) with R-19 batt insulation in wall

cavities.

2. ½” drywall (both sides) with R-19 batt insulation in wall cavities.

3. 7/16” OSB (front side) and ½” drywall (back side) with SPF in wall cavities.

4. ½” drywall (both sides) with SPF in wall cavities.

The four test panels were framed using 20-gauge steel studs placed vertically at 24 in.

on center. One or both sides of the panels were clad with ½ in. thick drywall sheet. As


before, all drywall joints were taped and finished with drywall compound. Results are

shown in Table 2.2.

Table 2.2 – Maximum Racking Load of Wall Panels (lbs) (NAHB 1996) Insulation Front & back

cladding materials R-19 batt insulation

SPF insulation

% Increase in racking strength

OSB & drywall 4,800 6,000 25%

Drywall & drywall 2,400 5,380 124%

The 1996 NAHB report notes that the SPF-insulated wall panels failed by buckling of the

steel framing whereas the batt insulated wall panels had sheathing failure. The racking

strengths of both of the SPF insulated wall panels increased over the corresponding batt

insulated panels. The racking strength of the SPF insulated panels was close (within

700 lb of each other).

2.1.1 Discussion of NAHB Results

The 1992 NAHB test series showed that SPF insulation provided an overall

improvement in the racking strength of non-structural cladding wall panels as shown in

the results. SPF insulation increased the racking strength of these wall panels by 207%

and 83% respectively for the vinyl and T1-11 systems.

SPF-insulation is shown to have a beneficial impact on the racking strengths of

conventional walls as well as walls having non-structural cladding installed on one side.

The SPF-insulated panels also appear relatively insensitive to changes in wall stud

spacing as changing the stud spacing from 16 in. o.c. (7 studs) to 48 in. o.c. (3 studs)

only reduced the racking strength by 18 %. This result suggests there are structural


benefits of the composite action of the SPF and sheathing that outweigh the effect of

different sheathing materials.

The results of the 1996 NAHB tests also suggest that SPF-insulation has positive

benefits to the racking strength of wall panels. However, these results are less reliable

than the earlier experiments as only one test was performed for each wall configuration

thereby the results are susceptible to experimental error. Limited value can be derived

since only one test was conducted on each panel configuration.

While the results show significant improvements in racking strength performance in the

experimental wall panels, it is uncertain how well these can be extrapolated to an actual

building. Since the tested wall panels were only 8 ft long, the plywood bracing panel

occupied 50% of the wall length, whereas in a typical wall of a residential building, the 4

ft wide plywood sheet is more likely to represent a smaller fraction of the overall wall

length. No tests provide data on how varying the percentage of structural sheathing

would change the results but this researcher suspects that racking strengths for a long

wall section is likely to be lower than the values reported in the NAHB studies.

2.2 Using Adhesives as a Retrofit Measure for Roofs in High Wind Areas

The use of structural adhesives as a retrofit measure to mitigate hurricane damage to

house is not new. Currently, there are structural adhesives on the market that have been

used in this manner (e.g. Alpha Foamseal Hurricane Adhesive)

[http://www.alphafoamseal.com/index.html]. The Alpha Foamseal website claims that

this structural adhesive, which was tested at Clemson University, hardens to create a

watertight seal that acts as a secondary water barrier in wood roof structures.


Jones (1998) conducted wind uplift tests using several roof sheathing materials panels

to evaluate the effectiveness of the adhesive for retrofit and new construction of wood

roofs. Jones’ tested SPF adhesives in two areas, a) sheathing-to-wood member

connection and b) roof member-to-wall plate connection, which are discussed in the

following sections.

2.2.1 Retrofit Structural Adhesive of Sheathing-to-Wood Member Connection

Jones (1998) conducted suction tests on 4 ft by 8 ft roof sheathing panels in a pressure

chamber loading the panels monotonically until failure. The sheathing used was 19/32

in. OSB and 15/32 in. 3-ply CDX plywood. Power-driven 8d common nails were used for

all of the specimens with a 6 in. on center nailing pattern along the edge wood members

and 12 in. on center along interior wood members. Jones tested a total of 97 panels

with 11 configurations including a control set of 19 panels. Retrofitted panels had a two-

part foaming adhesive sprayed continuously along the sheathing-to-wood member joints.

Jones found that the sheathing type affected the uplift capacities. Using the CDX

plywood (15/32 in.) the adhesive along with the nails provided about a 200% increase in

the uplift capacity of the sheathing over using just nails. Using the OSB (19/32 in.) the

adhesive along with the nails provided 100% to 300% increase in the uplift capacity of

the sheathing over using just nails depending on the amount of adhesive used. Jones

also found specimens constructed using southern yellow pine (SYP) wood members had

approximately 15% lower ultimate failure capacities than those constructed using

spruce-pine fir wood members. Jones suggested that higher wood density (of the SYP)

hinders absorption of the adhesive into the wood. Jones did not consider in-plane shear

forces along the wood members that are resisted by the roof diaphragm and transferred

through the roof member-to-sheathing connection to the roof members.


2.2.2 Retrofitting Roof Truss-to-Wall Plate Connections

Jones (1998) also considered using adhesives as a retrofit measure for the toe-nailed

roof-to-wall connections. This type of connection is known to be a weak one that is

responsible for hurricane damage to roof structures in past storms. In much of the older

residential construction the roof-to-wall connections were made using 2 or 3 nails toe-

nailed (driven through side of one member into a supporting member) into a connection.

As a result, under wind uplift loads these nails are placed in withdrawal and they have

very low capacities. Several retrofit techniques are available for these connections

including metal straps (i.e. Simpson Strong-Tie H2.5 and H10 hurricane straps). Using

structural adhesives is another possible approach.

Jones constructed four configurations of retrofitted roof-to-wall connections retrofitted

with a one-part polyurethane adhesive that was applied between the roof and wall

members and the wood blocks (Figure 2.1). The results were compared with failure

loads of non-retrofitted roof-to-wall connections that were fastened only with three 8d

common nails. Table 2.3 provides a summary of the results.

Toe-nailed connections had average uplift capacities of 429 lbs and 343 lbs for SYP and

spruce-pine-fur wood members, respectively. Jones found that when using the adhesive

connections made using SYP had higher uplift capacities (15-40% more) than spruce-

pine-fur connections. In addition, when more adhesive was used (double pass) the uplift

capacity of the connection increased. Jones also found that the blocks with more

surface area contact with the wood members produced a higher ultimate uplift capacity

(i.e. Block D uplift capacity was larger than Block E).


(a) Block A – 3.5”x1.5”x1.5”

(b) Block C – 0.75”x1.5”x3.5”

(c) Block D – 3.5”x1.5”x3.5”

(d) Block E – 3.5”x1.5”x1.5” with notch

Figure 2.1 – Roof-to-Wall Connection Retrofit Methods Using Adhesives (from Jones 1998)

Table 2.3 – Summary Results of Using Adhesive as a Retrofit for Roof-to-Wall Connections (Jones 1998)

Southern Yellow Pine Spruce-Pine-Fir Connection

Configuration Mean (psf)

% Increase Over Control

Sample Size

Mean (psf)

% Increase Over Control

Sample Size

Control (nails only) 429 N/A 20 343 N/A 20

Block A, single pass of adhesive 1146 167 20 1000 192 20

Block A, double pass of adhesive 1891 341 20 1513 341 20

Block C, single pass of adhesive 700 63 20 N/A N/A N/A

Block D, double pass of adhesive 1691 294 18 832 143 19

Block D, no toe-nails 3475 710 20 2959 763 20

Block E, toe-nails 3246 657 19 2365 590 20


2.2.3 Discussion of Roof Truss-to-Wall Plate Retrofits

It appears that the amount of surface area between the block and the wood members

has a significant influence on the ultimate capacities of these connections as well as the

amount of adhesive used. Increasing the wood block surface area increases the uplift

capacity. In addition, increased the amount of adhesive also increases the uplift

capacity. The amount of adhesive is also dependent on the amount of surface area.

Blocks D and E have the highest uplift capacities due to large amount of surface area

and subsequent larger amounts of adhesive.

Jones noted that in order to achieve a strong adherence between the wood components,

the adhesive must be applied to clean surfaces, free of dust and particles. For a retrofit

application in an older, existing home, this may be difficult (or sometimes impossible) to

achieve. In addition, the ease of placement of these retrofits in the confined space of a

residential attic with typical sloping roofs could also be problematic. In some cases, the

the ceiling or the roof sheathing may have to be removed and replaced in order fully

access and clean the location, which increases the retrofit cost. As a result, the use of

spray-applied adhesives to retrofit the roof truss to wall plate connection may not be

suitable for all residential buildings. However, if the retrofit can be installed without major

work to get access, the additional uplift capacity of this critical connection would be

significant.


3. EXPERIMENTAL INVESTIGATION of ccSPF RETROFITTED PANELS

3.1 Research Objectives

This research and experimental program consists of three primary phases:

1. Experimental Tests to Determine Wind Uplift Resistance of Wood-Framed

Roofing Panels – Investigate the structural benefits (if any) of ccSPF in improving

uplift resistance of wood-framed residential roofing.

2. Design Wind Load Calculations of ccSPF Adhesive – Illustrate by structural

analysis calculations the potential benefits (if any) of ccSPF adhesive in retrofit

application to improve wind uplift capacity of roof truss-to-wall plate connection.

3. Literature Review

• Research through existing scientific literature and reports the benefits (if any)

of sealed attics versus vented attic construction for residential construction.

• Determine based on NAHB racking test data the benefits (if any) of ccSPF

applied to a wood-framed/plywood shear wall to improve the shear capacity

of the wall.

4. MATERIALS AND METHODS

University of Florida civil engineering undergraduate and graduate students fabricated

the test panels. Xtreme Foam, Inc., a spray-foam applicator installed the ccSPF.

Xtreme Foam Inc., located in Orlando, FL, is a professional spray foam contractor that

installs InsulStar®, a 2.0 pcf closed-cell spray foam formulated by NCFI Polyurethanes.

24 of 34 panels that were constructed on March 12, 2007 were sprayed with NCFI

InsulStar® ccSPF on March 15, 2007. A second set of 15 panels was fabricated on

June 17, 2007, 10 of which were sprayed with ccSPF on June 29, 2007.


The testing procedure followed a modified ASTM E330-02 procedure (Standard Test

Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain

Walls by Uniform Static Air Pressure Difference) (ASTM 2004) where the pressure

application was limited to only one direction (suction within the chamber) and no

deflection readings were measured.

4.1 Test Chamber

We conducted pressure tests using a 6 in. deep steel pressure chamber that measured

4 ft 6 in. by 8 ft 6 in. in plan. The chamber walls are hot-rolled channel members welded

to each other at the corners and continuously welded to a steel sheet base. One

chamber wall has a 2.0 in. diameter hole that is connected to a vacuum pump by PVC

pipe. Two 0.5 in. diameter threaded holes are tapped into the chamber wall for

connecting the pressure gauges.

Two vacuum pumps were used for the testing, as detailed in Table 4.1, because the first

pump failed and had to be replaced. The test setup (for Pump #2) is shown in Figure

4.1. The chamber pressure is adjusted using two valves; a) gate valve to adjust intake

of outside air and b) T-valve that closes off the test chamber or the pump, if needed.

Table 4.1 – Pertinent Pump Specifications

Pump # Model # Serial # Maximum

CFM

Maximum Pressure

(psf) Pump Type Specimens

Tested

1 Graham

LX180/10/43/M/K1

066847VP 82 760 Liquid Ring Vacuum

1-3, 6, 12, 14-36

2 US Vacuum CP15 8817 15 2100 Rotary Vane

Single Stage 5, 7-9, 11, 13, 1A-5C


Pressure Gauges

Atmospheric AirIntake Gate Valve

Tee Valve

Pump

Pressure ChamberPressure Gauges

Atmospheric AirIntake Gate Valve

Tee Valve

Pump

Pressure Chamber

Figure 4.1 – Suction Chamber Pump and Controls (Pump #2)

4.2 Roof Sheathing Panel Construction

Roof panel specimens were fabricated using ½” by 4 ft by 8 ft oriented strand board

(OSB) sheathing and Southern Yellow Pine (SYP) 2 in. by 4 in. framing members. The

wood was purchased on March 9, 2007, from Contractor’s Supply, Gainesville, FL.

Norbord, an APA-The Engineering Wood Association certified producer, manufactured

the OSB sheathing for Exposure 1, with a 32/16 rating. K-D Wood Products Inc.

produced the No. 2 grade SYP wood members.

The OSB sheathing was fastened to the wood using two (2) power-driven nail sizes in

two phases. The first 34 panels used 8d ring shank nails, and the second set of 15

panels used 6d common nails (Table 4.2). We installed the nails using a framing gun,

Bostitch Model No. F21PL (Serial No. N88RH-2MCN) powered using compressed air

supplied at 40-45 psi. All OSB panels were installed with the interior surface in contact

with the framing members.


Table 4.2 – Properties of Nails Used in Test Panel Specimens

UF Test Nails NDS, Appendix L (AF&PA 2001)

ESR-1539, Table 1 (2005) Quantity

6d Common

8d Ring Shank

6d Common

8d Common 8d Ring Shank

Shaft Diameter (in.) 0.112 0.123 0.113 0.131 0.120 Head Diameter (in.) 0.28 0.313 0.266 0.281 n/a

Length (in.) 2.0 2.49 2.0 2.5 2.5

The wood members for each test specimen were 5 ft long so that the edges rested on

the vertical sides of the pressure chamber. Unlike in roof construction, the end members

of each panel were not centered along the edge of the sheathing but instead were

placed with their outer face flush with the edge of the sheathing (Figure 4.2). Care was

taken to consistently install nails true and at the 6”/12” fastening schedule, with nails

spaced 6 in. apart on the exterior members and 12 in. apart along the interior wood

members.

6"

48"

6"

Edge nailing@ 6" o.c.

Interior nailing@ 12" o.c.

24" 24" 24" 24"96"

Figure 4.2 – Test Specimen Layout and Nail Schedule


4.3 ccSPF Application

During the spray-foam installation, the applicator wore a Tyvex suit, full facemask and a

breathing apparatus (Figure 4.3). The ccSPF is made by combining two chemicals (a

two-part process), Part A and Part B. Part A or “A-side” is an isocyanate liquid (di-

phenyl methane di-isocynate or MDI) manufactured by Huntsman. Part B or the “B-side”

is a proprietary liquid resin blend manufactured by NCFI Polyurethanes under the

InsulStar® brand. The B-side blend consists of polyester and polyether polyols, blowing

agents, surfactants, catalysts, fire retardants, UV inhibitors and dyes. In this formulation,

Honeywell Enovate® HFC245fa blowing agent is used. When properly applied by a

trained applicator, the foam will have the physical properties defined by the InsulStar®

data sheet (see Appendix B). The two chemical products are transported in separate

containers to the site, and they are mixed using a spray foam machine under high

pressure (1000 psi) during application. The test panels were laid out the ground on a

plastic sheet, OSB sheathing side down and the ccSPF was sprayed to the panels.

Figure 4.3 – Application of Second Lift of ccSPF for the Full Foam Specimens

The 49 test specimens were divided into three treatment groups (Table 4.3), as follows:

• Configuration A (Control): ½ in. by 4 ft x 8 ft OSB/wood roof panel (described

previously, see Section 4.2).


• Configuration B (Foam Fillet): Configuration A, plus an application of a ccSPF

fillet adhesive between wood members and roof sheathing, (see Figure 4.4(a)).

• Configuration C (Full Foam): Configuration A, plus a 3 in. thick full coverage of

ccSPF foam layer between the wood members (see Figure 4.4(b)).

(a)

(b)

Figure 4.4 – ccSPF Application: (a) Configuration B – Foam Fillet, (b) Configuration C – Full Foam

Table 4.3 – Test Specimen Configurations

Nail Type Configuration A Configuration B Configuration C Total

8d ring shank 10 13 11 34

6d common 5 5 5 15

Totals 15 18 16 49

The ccSPF fillets in the Configuration B specimens were sprayed along either side of

interior wood members and on one side of the exterior members (see Figure 4.5). In the

two fabrication phases, different application techniques were used to apply the ccSPF

fillets to the panels. In Phase 1, the rectangular nozzle of the spray gun was oriented


with the long dimension parallel to the wood member axis (Figure 4.5(a)), whereas in

Phase 2, the nozzle was oriented with its long dimension perpendicular to the wood

member (Figure 4.5(b)). As a result, the Phase 2 fillets were wider and taller than the

Phase 1 fillets, with apparently greater contact area between the ccSPF and OSB

sheathing and wood members.

(a)

(b)

Figure 4.5 – ccSPF Foam Fillets: (a) Phase 1 Fillet and (b) Phase 2 Fillet

The full ccSPF coverage (Configuration C) foam was installed in two layers or lifts as, we

are told, is the practice in residential insulation projects. Application of closed-cell

ccSPF in two lifts is required to achieve optimum foam properties. If sprayed in a single

pass to achieve a 3.0 in. thickness, the exothermic reaction can negatively affect the

foam properties. The first lift was approximately 1.0 to 1.5 in. thick and the second lift

completed the 3 in. thickness. The ccSPF rapidly hardens once sprayed onto the

panels. About 15 minutes after spraying, the panels were moved into the dry storage

facility and covered with a tarpaulin to allow the ccSPF to cure for a minimum of 7 days.

4.4 Test Procedure

The testing method is modified from ASTM E330-02 (Standard Test Method for

Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by


Uniform Static Air Pressure Difference) procedure (ASTM 2004). Currently no standard

test procedures exist for the determination of wind uplift performance of wood roof

structures. The main modifications to ASTM E330 test procedure were as follows:

• pressure is applied in one direction only, i.e. suction or reduced pressure within

the test chamber,

• no deflection readings are taken to record permanent deformation of the panels,

• the chamber pressure is reduced in 15 psf increments, applied and maintained

for approximately 10 seconds, and

• the recovery period for stabilization is not used.

Test specimens were placed on the chamber, sheathing side down, with wood members

spanning the short dimension of the chamber. The test specimen was loosely covered

with a single thickness of 2 mil (0.002 in.) thick polyethylene film so that the membrane

did not prevent movement or failure of the specimen. The polyethylene film had extra

folds at the corners and around the wood members, so that when the pressure is applied

there were not fillet caused by tightness or the plastic. The plastic film was adhered to

the test chamber walls using duct tape (3M L155-XW) to create an airtight seal (see

Figure 4.6).


Figure 4.6 – Suction Chamber with Roof Panel and Plastic

We reduced the chamber pressure by slowly closing the gate valve at the atmospheric

air inlet. We reduced the chamber pressure in 15 psf increments, which was held

constant for 10 seconds at each pressure increment. We measured the chamber

pressure using a general-purpose digital pressure gauge (Omega, Model No. DPG8000-

VAC; Serial No. 1015044), which is calibrated in inches of mercury (inHg) (1 inHg =

70.73 psf). The test proceeded in this manner until panel failure occurred and the peak

pressure recorded. We removed the plastic sheet and at failure and examined the

specimen to determine its failure mode and other pertinent information.

5. RESULTS AND OBSERVATIONS

5.1 Failure Modes for ccSPF Retrofitted Roof Panels

We observed five distinct failure modes in the roof panels. This section briefly describes

these failure modes. Failure can occur in the sheathing (nail pull-through), in the wood

member (nail withdrawal or wood fracture) or in the ccSPF itself. For this discussion, the

wood member and sheathing are called the adherents and the ccSPF, the adhesive

(Figure 5.1).


Figure 5.1 – Adhesive Failure Modes (from http://wikipedia.org)

• “Cohesive” Fracture – A crack propagates through the adhesive and

portions of the fractured adhesive remain on the adherent material (wood

members and sheathing).

• “Adhesive” or “Interfacial” Fracture – Debonding occurs between the

adhesive and the adherent. For ccSPF application to wood, adhesion is

achieved by mechanical means with the adhesive working its way into small

pores in the wood instead of a chemical bond.

• Mixed Fracture – Failure occurs if the crack propagates as a cohesive

fracture in some places and as an adhesive fracture in other places.

• Alternating Crack Path – The crack jumps from one interface to the other

due to tensile pre-stresses in the adhesive.

• Fracture in the Adherent – The adhesive remains intact but the adherent

fractures due to a tougher adhesive than adherent.


5.2 Phase 1 Testing

Table 5.1 provides wind uplift capacities of the Phase 1 roof panels tested. Appendix A

provides observations about each individual panel.

Table 5.1 – Ultimate Failure Pressures of Test Specimens (Phase 1)

Configuration A Configuration B Configuration C Date of Test Sample

ID # Pressure

(psf) Sample

ID # Pressure

(psf) Sample

ID # Pressure

(psf)

4/5/2007 27 88 26 158 12 252a

4/6/2007 28 70 22 126 2 285

29 100 24 165 3 267a,b

4/18/2007 30 46 1 238

4/20/2007 19 154 6 180a

4/21/2007 31 85 21 163

32 85 18 192

17 179

16 106

15 106

14 168

20 168

5/14/2007 33 71 23 135

34 90 25 170

35 71

36 71

Mean (psf) 77.7 154.9 244.7

Std. Dev. (psf) 15.16 25.65 39.94

COV (%) 19.5% 16.6% 16.3%

a. Failure occurred at a knot in the wood member. b. Nail heads removed prior to testing.


The initial specimens were tested in a sequential order (a panel from A then B then C) to

ensure uniformity in the test sequence between panel configurations. On April 20, a

Configuration C panel (#13) was tested but vacuum pressure in the chamber would not

exceed a pressure of 212 psf. The panel did not fail at this pressure. The remaining

Configuration A and B panels were tested since their previous maximum failure

pressures were less than 200 psf. The pump worked correctly for these specimens but

a new pump was ordered that could attain a higher pressure and fail the Configuration C

panels. Specimen #13 was retested with the new pump in July and is recorded in

Section 5.3, Table 5.3.

The typical failure mode for Configuration A (control) panels was nail pull–through. The

ring shank nails remained in the wood members and the OSB sheathing failed locally

around them (see Figure 5.2). For Configuration B, the typical failure mode was the

nails pull-through (described above) and a combination of adhesive/cohesive failure of

the ccSPF at the sheathing and wood member interfaces. (see Figure 5.3). In some

cases, very little ccSPF material remained on the wood, indicating an adhesive fracture.

In other cases, a substantial amount of ccSPF remained on the wood, indicative of a

cohesive failure.

We observed three failure modes in the Configuration C (full coverage) panels:

1. The wood member separated from the foam on both sides leaving the foam

attached to the OSB sheathing. The wood member sometimes had little to

no foam residue remaining on the wood member (adhesive fracture) and

sometimes a significant amount of foam residue was evident (cohesive

fracture).


2. The wood member separated on one side from the foam (usually an

interfacial fracture) and on the other side the foam remained attached to the

wood member but separated from the OSB sheathing (cohesive failure).

Whenever the foam separated from the sheathing, approximately 5-10 inches

of foam would remain on the wood member.

3. One of the wood members would split (adherent fracture) always at a knot in

the wood.

Figure 5.2 – Typical Failure Mode of No Foam Specimens using 8d Ringshank Nails

(Nail Heads Pulled Through Sheathing)

Figure 5.3 – Typical Failure Mode of Foam Fillet Specimens (Phase 1)


5.3 Phase 2 Testing

Phase 2 of the ccSPF panel tests consisted of a second set of specimens tested July

18-19, 2007, using Pump 2. Fifteen specimens were tested in three configurations (A,

B, and C) with five replicates each. The only difference in these specimens from the

earlier specimens was Configuration B – the foam fillet. The fillet for this set of five was

applied perpendicular to the wood member as opposed to parallel with it as was the

case with the first set (see Figure 4.5, Section 4.3). Table 5.2 shows the data from these

testing days.

Table 5.2 – Phase 2 ccSPF Uplift Testing Conducted July 2007

Configuration A Configuration Bb Configuration C Date of Test

Sample ID #

Pressure (psf)

Sample ID #

Pressure (psf)

Sample ID #

Pressure (psf)

7/18/2007 1A 75.0 1B 194.5 1C 282.9a

2A 105.4 2B 178.2 2C 246.1

3A 71.4 3B 178.2

7/19/2007 3C 200.2a

4A 76.4 4B 146.4 4C 253.9

5A 46.7 5B 177.5 5C 268.8

Mean (psf) 75.0 175.0 250.4

Std. Dev. (psf) 20.86 17.50 31.42

COV (%) 27.8% 10.0% 12.5%

a. Failure occurred at a knot in the wood member. b. Spray nozzle long dimension held perpendicular to wood member longitudinal axis.

The typical failure mode for Configuration A was nail pull out—nails remaining in the

sheathing and pulling out of the wood members. On one test (#5A), one of the end nails

on the center wood member pulled through the sheathing. It was observed that this nail

was closer to the edge of the sheathing than other end nails. During this test (#5A) slow


nail withdrawal of the sheathing from the wood members was initiated on the side where

the nail had pulled through the sheathing. By the time the test was stopped, the nail on

the opposite end of the wood member had just started to withdraw from the wood

member evidenced by a small visible separation between the wood member and the

sheathing at the end.

There were two typical failure modes of the Configuration B specimens during Phase 2

testing. The first failure mode was separation of the wood member from the foam on

both sides (see Figure 5.4(a)). This separation from the wood member was sometimes

an interfacial fracture evidenced by no foam residue remaining on the wood member.

Sometimes we observed a cohesive failure evidenced by significant foam residue

remaining on the wood member. The other failure mode was separation of the foam

from the sheathing on one side of the wood member (cohesive failure) and separation

from the wood member on the other side (interfacial fracture) (see Figure 5.4(b)).

(a)

(b)

Figure 5.4 – Typical Failure Modes for Configuration B on Phase 2 Testing


There were four different types of failure modes for the Configuration C specimens.

1. The wood member separated from the foam completely and the foam remained

intact on the sheathing (see Figure 5.5). The separation from the wood member

was sometimes an interfacial fracture evidenced by no foam residue on the wood

member and sometimes a cohesive failure evidenced by significant foam residue

remaining on the wood member (see Figure 5.6(a)). Sometimes when

separation occurred from the wood member, approximately half of the wood

member (in the 3.5 in. dimension) would have significant foam residue remaining

and the other half would not (mixed failure) (see Figure 5.6(b)). This is most

likely due to one of the lifts of foam achieving a stronger bond with the wood than

the other lift.

2. The foam separated from the sheathing but remained intact on the wood member

(see Figure 5.7). In this failure mode, the failure was always a cohesive failure

since there was always significant foam residue remaining on the sheathing.

When the foam remained on the wood member and separated from the

sheathing, the amount of foam that broke from the sheathing was nearly

constant. Approximately a 7-8 in. width of foam would remain attached to the

wood member (see Figure 5.7).

3. A combination of failure modes 1 and 2 above (see Figure 5.8).

4. The wood member failed by splitting (adherent failure) and occurred twice in the

five specimens. It was observed that the failure occurred at a knot in both of the

wood members (see Figure 5.9).


Figure 5.5 – First Failure Mode of Configuration C (Phase 2)

(a) Interfacial failure

(b) Mixed failure (c) Cohesive failure

Figure 5.6 – Foam Residue Levels on Wood Members at Failure for Configuration C (Phase 2)

~8 in.

~8 in.

~8 in.

~8 in.

Figure 5.7 – Second Failure Mode of Configuration C (Phase 2)


~8 in.~8 in.

Figure 5.8 – Third Failure Mode of Configuration C (Phase 2)

Knot in wood memberKnot in wood member

Figure 5.9 – Fourth Failure Mode of Configuration C (Phase 2) Several (6) Configuration C specimens constructed at the same time as the original

specimens in March 2007, were tested approximately 4 months after the original

specimen tests. These six specimens were tested on July 19-20, 2007. All of these

specimens had a significant bowing effect. When laid on the suction chamber, the

exterior wood members did not touch the chamber. The gap between the wood


members and the chamber was 0.5 to 1.125 in. These six panels were stacked on top

of one another and stored in the dry storage facility during the four months from

construction to testing. Specimen #9 also had one of the wood members skewed at an

angle of approximately 60º from horizontal (see Figure 5.10). All of the nail heads had

already pulled almost all of the way through the OSB sheathing, yet no visible separation

of the foam from the wood was noticeable. The failure of this member was a cohesive

fracture on one side of the member through the foam since a large section of foam

remained attached to the wood member (see Figure 5.11(a)). On the other side of the

wood member, a mixed fracture was evident due to significant amounts of foam

remaining on the member in some places and little to no foam in other places (see

Figure 5.11(b)). After failure, we observed that a significant amount of foam had actually

been between the wood member and the OSB sheathing (see Figure 5.11(a)).

Figure 5.10 – Wood Member Initially Twisted on Test Specimen #9


(a)

(b)

Figure 5.11 – Failure of Wood Member Initially Twisted on Test Specimen #9

Table 5.3 shows the raw data from these six tests. The failure modes were similar to

those for the Configuration C specimens sprayed with ccSPF on March 15, 2007.

Table 5.3 – Phase 1 Configuration C Specimens Tested July 19-20, 2007

Date of Test Sample ID # Pressure (psf)

7/19/2007 7 178.9

5 240.5

7/20/2007 11 237.6

13 253.2

9 139.3

8 269.5

Mean (psf) 219.8

Std. Dev. (psf) 49.9

COV (%) 22.7%


6. DATA ANALYSIS

A statistical analysis of the data gathered on the ccSPF specimens was performed,

assuming a 0.05 (α = 0.05) significance level for all tests. Our F-test on the data set

showed that the variances of each treatment (Configurations A, B & C) from Phase 1

and Phase 2 should be the same. In addition, the Student’s t-test on the mean values of

each treatment did not show any significant differences in means between Phase 1 and

Phase 2 results, despite the fact that physically several specimen characteristics had

changed (nail, type, cupping of sheathing in Phase 2, ccSPF color, cure time of ccSPF,

etc.).

For Configuration B, the mean uplift capacities between Phases 1 and 2 were not

significantly different from each other, despite longer cure time in Phase 1 and

application method of fillet (see Figure 4.5, Section 4.3).

Figure 6.1 shows a comparative boxplot of these two different foam fillets. The top and

bottom of the vertical lines in the boxplot represent the spread of the data, and the

lowest and highest horizontal lines in the boxplot represent the first and third quartiles of

the data respectively. The middle horizontal line represents the median. The results

suggest that the larger fillet (constructed June 2007) has a higher overall resistance and

less variability possibly due to the fact that there is a larger area to which the foam

adheres.


Pan

el F

ailu

re P

ress

ure

(psf

)

June/JulyMarch/April

200

190

180

170

160

150

140

130

120

110

100

Configuration B Construction/Test Dates

Figure 6.1 – Comparative Boxplot of Configuration B Showing the Difference in the Fillet Application

We found no statistically significant difference in the uplift capacity between the six

Configuration C specimens that cured for 12 weeks versus those that were only cured

for 3 weeks, although the mean uplift capacity of the specimens that had cured longer

was lower by 25 psf. Therefore, we conclude there is no strength degradation due to

aging at the 0.05 confidence level.

Figure 6.2 shows a comparative boxplot of the Configuration C specimens grouped by

both fabrication date and test date for the specimens. The longer cured specimens (the

March/July group) show a larger spread in the data, as well as the lowest failure values

of the three groups. One of these Configuration C panels actually failed at uplift

pressure of 140 psf or 20 psf lower than mean uplift capacity of the Configuration B

panels. While this is an extreme value, we do not see evidence that this value is an

outlier that should be removed from the analysis. However, the larger spread and low


failure values suggest that the variability in uplift capacity increases with ccSPF foam

age.

Pan

el F

ailu

re P

ress

ure

(psf

)

March/JulyJune/JulyMarch/April

300

275

250

225

200

175

150

125

Configuration C Construction/Test Dates

Figure 6.2 – Boxplot of Configuration C Test Specimen Groupings

We concluded from our t-test analysis that there is insufficient evidence to conclude that

the cure times were a factor in the results and so it was permissible to group together all

data for each treatment (Configurations A, B, and C) tested.

Figure 6.3 shows a comparative boxplot of the combined data sets (ignoring cure time)

for the three configurations. The spread in the data is largest in Configuration C due to

the older specimens. Table 6.1 gives a summary of our data analysis and the

confidence intervals for each configuration.


Pan

el F

ailu

re P

ress

ure

(psf

)

CBA

300

250

200

150

100

50

0

Configuration

Figure 6.3 –Boxplots of Failure Pressure of the Combined Data for All Panel Configurations

Table 6.1 – Combined Data Summary Statistics for All Panel Configurations Configuration

A B C

Mean (psf) 76.8 160.5 237.2

Std Dev (psf) 16.55 24.94 41.44

COV (%) 21.6% 15.5% 17.5%

Minimum (psf) 46.0 106.1 139.3

Maximum (psf) 105.4 194.5 285.0

Number of Samples 15 18 16

95% Confidence Level (psf) ±9.2 ±12.4 ±22.1

95% Confidence Level as Percentage of Mean ±11.9% ±7.7% ±9.3%

95% Confidence Level (Lower Bound) (psf) 67.6 148.1 215.1

95% Confidence Level (Upper Bound) (psf) 86.0 172.9 259.2


Further, our t-test analyses showed overwhelming evidence that the mean values for the

three configurations differed significantly from each other (with P-values approximately

10-6 to 10-12). In other words, the mean uplift capacity of the Configuration B panels

(foam fillet) was significantly greater than mean value for the Configuration A (no foam)

panels. Similarly, the mean uplift capacity of the Configuration C panels (full foam)

panels indeed is significantly larger than either the Configuration A or B panels tested.

7. DISCUSSION OF RESULTS

7.1 Nail Pullout

Table 11.2C of the National Design Specification (NDS) (AF&PA 2001) provides

allowable nail withdrawal strengths in wood, which according to McLain (1997) assumes

a factor of safety of 6.0. Ring shank nails have higher withdrawal strengths over the

equivalent size common nail, e.g. the withdrawal strength of an 8d ring shank nail

fastened in southern yellow pine (SYP) is 46 lbs per in. penetration versus a 41 lbs per

in. withdrawal strength for an 8d common nail driven into the same material (using a

specific gravity of 0.55).

It is reported in the technical literature (i.e., McLain (1997)) that ring shank nails can

provide improved withdrawal resistance. This withdrawal strength is highly dependent

on several factors, including geometry of the threads, head size, manufacturing quality,

etc., and there are few standards to ensure uniformity. The NDS does not provide any

values for nail pull-through strengths for any roof sheathing materials. Chui and Craft

(2002) conducted tests that showed nail pull-through strengths need to be accounted for

in the design of fasteners. Using ½ in. thick OSB and Canadian soft plywood (CSP)


their results confirmed that nail head pull-through failures can occur at lower loads than

the nail withdrawal capacities.

In the 2007 UF roof panel wind uplift tests, we observed two failure modes; a) nail

withdrawal from the wood member and b) nail head pull through the OSB roof sheathing.

The first failure mode occurred in configuration panel tests where panels were fastened

with 6d common nails. Nail pull through failures were observed in all other tests (8d ring

shank nails). The mean failure pressures of Configuration A panels fastened with 6d

common and 8d ring shank nails were 75 psf and 78 psf respectively. These failures

values represent two failure modes – nail withdrawal and nail pull-through respectively.

The observed failure mode of the panels fastened with 8d ring shank nails is the nail

pulling through the ½ in. OSB sheathing. There is no statistical difference in the mean

failure loads of the ccSPF retrofitted panels using 8d ring shank or 6d common nails at a

0.05 significance level for the three individual configurations. Figure 7.1 shows a 95%

confidence level interval for the mean failure load of the three configurations tested with

respect to nail failure mode.


Pre

ssur

e (p

sf)

WithdrawalPull ThroughWithdrawalPull ThroughWithdrawalPull Through

300

250

200

150

100

50

0

Configuration A Configuration B Configuration C

Figure 7.1 – Comparing Mean Failure Pressure and “Nail” Failure Mode (Tick marks show the 95% confidence intervals for the mean failure load)

The wind uplift resistance of Configuration A is controlled by the lower withdrawal

capacity of the 6d common nails and not by flexural behavior of the OSB sheathing. The

major factors affecting nail pullout resistance are length of penetration of the fastener

into timber member, the density of wood, fastener diameter, and shank profile. Chui and

Craft (2002) showed that the mean pull through load was the same for ½ in. OSB and

softwood plywood but the variability in the OSB results was much larger.

7.2 ccSPF Foam Retrofit

7.2.1 Configuration B – Foam Fillet

The ccSPF fillet in the Configuration B panels increases the uplift capacity of the roof

panels by 2.1 times the capacity using only nails (Configuration A). As mentioned

earlier, the foam fillets in the Configuration B panels were applied using two different

techniques (Section 4.3 and Figure 4.5), but the difference in results was not statistically

significant. However, the reader is cautioned that the relatively small sample sizes may

be insufficient to conclusively determine apparent differences. Further testing is


warranted. Although the coefficients of variation were almost equal (16.6% versus

15.5%), it appears that ccSPF application is better controlled and more consistent

(visually) when the fillet is applied perpendicularly to the wood member, and a larger

volume of ccSPF is required. We suspect that greater control in application technique

will minimize the variability in the strength of the fillet and hence in uplift capacity.

We also noted that the size of the ccSPF fillet is proportional to the application rate

and/or speed that the spray nozzle moves along the wood member. With slower nozzle

moving speed, more foam is applied in a given area at a given time. Therefore, it should

be no surprise that that the ultimate wind capacity is related to the application technique

and to the skill of each applicator.

7.2.2 Configuration C – Full Foam

Application of a 3 in. thick ccSPF layer (Configuration C) over the panel resulted in a 3.1

time increase in uplift capacity over using just nails (Configuration A). The following

sections describe various points of interest in the failure capacities of these specimens.

7.2.2.1 Wood Member Failure

In five specimens (#3, 6, 12, 1C, and 3C) a wood member failed during testing. Failure

always occurred at a knot in the wood, and all failures (except #3) were at interior wood

members. The average uplift failure load of these five panels is 236.6 psf with a COV of

18.7%. The difference between the two extreme failure loads for these five panels is

more than 100 psf. In fact, three of the five failure loads are greater than 250 psf which

is more than the overall average uplift failure load and the average uplift failure loads of

their respective groups (Phases 1 and 2). The fact that three wood member failure

pressures are greater than the overall uplift failure pressure indicates that the failure of

the wood members does not seem to be an issue with respect to the ultimate failure


loads. In addition, if the five wood member failure loads are removed from the data set,

the overall mean uplift failure loads of the Configuration C panels is 237.4 psf with a

COV of 17.8% compared to 237.2 psf and 17.5% when the panels are included.

Therefore, the wood member failure is not significant with respect to the ultimate

capacity of the ccSPF itself.

7.2.2.2 “No Nail” Uplift Test

Prior to testing Specimen #3, a full foam retrofit panel (Configuration C), we removed the

nail heads using a grinder in order to determine the holding power of the ccSPF itself.

We assumed that the nail without its head provides no resistance to sheathing

withdrawal from the wood members. With this modification, the Specimen #3 failed at

an impressive 267 psf, or approximately 20 psf higher than the mean uplift capacity of

the Configuration C, Phase 1 specimens. The failure mode was not even in the foam

itself, rather one of the exterior wood members failed at a knot. None of the other wood

members separated from the foam or the OSB sheathing.

While this test provided only one data point, which is insufficient to draw any statistical

conclusions, it provides anecdotal evidence of the potential retrofit advantage of the

ccSPF layer. This observation warrants further testing in the future.

7.2.2.3 Aging Considerations

The test specimens tested after curing for four months also exhibited a lower mean uplift

capacity (219.8 psf) than those that cured for only 2 to 3 weeks (244.7 psf and 250.4

psf), even though statistically the mean uplift capacities were not different from each

other. Again, we consider the reduced strength of the older specimens is a cause for

further investigation.


Strength degradation of structural adhesives with time is a factor that needs to be

accounted for and can be a major issue when using adhesives in structural retrofits.

This phenomenon was discussed in the study (Jones 1998) reported in the literature

review. Until, further studies show otherwise, it is recommended that an “aging” factor of

safety should be used, if ccSPF is to be used as a structural adhesive in long-term (>6

months) applications. The safety factor should be determined through further testing

and/or reliability studies.

7.3 Panel Stiffness

Previous experimenters found that the panel stiffness influences the effectiveness of the

roof sheathing to wood member connection, especially for panels installed using

adhesives (Jones 1998). Excessive panel deflections can cause the adhesive to fail.

The stiffness of a roof panel can be increased in several ways: by increasing the

sheathing thickness, by reducing the spacing between wood members, or by, for

example, adding a structural foam layer, which creates a deeper composite section with

increased section moment. Jones (1998) also cautions that higher construction loads on

the roof after the adhesive is applied can cause the adhesive to crack or fail before uplift

loads are applied to the roof.

We can expect that if we change the roof sheathing material (i.e. using say a 19/32 in.

OSB or plywood instead of ½ in.), the pull-through resistance will also change (increase)

and once the pull-through resistance exceeds nail withdrawal strength a different failure

mode will occur.


8. DESIGN WIND UPLIFT LOADS ACCORDING TO ASCE 7-05

ASCE 7-05 (Minimum Design Loads for Buildings and Other Structures) (ASCE 2006) is

a standard published by the American Society of Civil Engineers provides baseline

structural loads for design of buildings. This standard is adopted and included in many

building codes across the country. Chapter 6 describes the approach to determine wind

design loads.

8.1 Roof Sheathing Wind Uplift Design Loads

The design loads for roof sheathing wind uplift loads are calculated according to the

(Analytical) Method 2 for Components and Cladding (C&C) described in ASCE 7-05

(Section 6.5). The C&C method divides the roof into three different zones with varying

design uplift pressures to account for the variability in suction loads on a roof (see Figure

8.1 for a description of the zones). The wind uplift loads presented in Table 8.1 are

determined for a building with a 30 ft roof span and roof pitch of 4 in 12 (18.4º). The

mean roof height is less than or equal to 30 ft. The upwind exposure is Category B

(suburban), and the design loads are calculated for wind speeds of 130, 150, and 170

mph. The design wind speed is a 3-second gust speed given at 33 ft above ground in

an open terrain. The building is assumed to be partially enclosed.


Figure 8.1 – Components and Cladding Roof Zones for 7º ≤ Θ ≤ 27º and h ≤ 60 ft (excerpted from

ASCE 2006 Figure 6-11C)

Table 8.1 – ASCE 7-05 Design Wind Pressures for Roof Sheathing Uplift* (psf)

Design Wind Speed (mph)

Zone 1 (Interior)

Zone 2 (Edge)

Zone 3 (Corner)

10 square foot effective area

130 -37.3 -57.9 -81.1

150 -49.7 -77.1 -108.0

170 -63.8 -99.0 -138.7

20 square foot effective area 130 -36.0 -54.1 -75.9

150 -48.0 -72.0 -101.1

170 -61.6 -92.4 -129.9

100 square foot effective area 130 -34.8 -45.0 -65.6

150 -46.3 -60.0 -87.4

170 -59.4 -77.0 -112.3

*Based on a suburban exposure with a mean roof height of less than 30 ft.


8.2 Roof-to-Wall Connection Wind Design Uplift Loads

Design wind uplift loads for the roof-to-wall connection are presented in Table 8.2. The

conditions are the same as for the sheathing uplift loads presented in Table 8.1. The

roof-to-wall connection loads, however, are calculated using the Main Wind Force

Resisting System (MWFRS) method in ASCE 7-05. There are effectively two different

loading patterns for this design (see Figure 8.2). Table 8.2 shows the maximum

resultant design loads.

Transverse Wind Loading

Longitudinal Wind Loading

Figure 8.2 – MWFRS Loading Patterns from ASCE 7-05 (ASCE 2006) Table 8.2 – Maximum Design Uplift Force for Roof-to-Wall Connections Using MWFRS*

Design Wind Speed

(mph) Maximum Design Uplift

Force (lbs)

130 1110

150 1480

170 1910

*30-ft roof span, 4:12 roof slope, <30 ft mean roof height, suburban exposure, partially enclosed

It is immediately obvious comparing these results with Jones (1998) findings that toe-

nailed connections of SYP wood members to walls with ultimate wind uplift capacity of

429 lbs are woefully inadequate (by a factor of 2.6 for SYP in 130 mph zones) to resist

uplift forces. Generally, the recent building codes have been revised to reflect this


knowledge, and toe-nailed connections are not allowed to be used in residential

construction. However, there remains a substantial inventory (the majority) of existing

homes that have not been retrofitted and are, therefore, susceptible to roof blow off.

Jones (1998) results showed that spray-applied structural adhesives used in

combination with wood blocking can increase the wind uplift resistance of the roof-to-wall

connections. Since the wind uplift capacities of the ccSPF-retofitted roof panels in these

tests provided a similar increase in uplift capacity as the earlier Jones tests, it is likely

that using ccSPF and wood blocking will also improve the uplift capacity of toe-nailed

roof-to-wall connections. However, to achieve consistent capacities in field application

as observed in the laboratory tests, the devil may be in the details. Issues such as

accessing the joints in confined attic spaces, preparing the wood surfaces and applying

the adhesive must be considered and tested.

9. CONCLUSIONS

• Experimental results have shown that applying a ccSPF fillet along wood roof

member can increase the wind uplift capacity of ½” thick OSB roof sheathing panels

by more that two times the uplift capacity of the a control panel fastened using only

nails. The results further also showed that a continuous 3 in. thick ccSPF layer can

increase the wind uplift capacity by as much as three times that of the control roof

panel.

• The use of SPF as a retrofit technique for roof member-to-wall connections needs

further validation through experimental studies, (listed below in Future Work). An

analytical model of the ccSPF retrofit will enhance its use as a structural adhesive.

However, extensive finite element modeling and testing is needed to make this so.


• The performance of aged ccSPF may be a factor in the uplift capacity of the

retrofitted roof panels suggested by the increased variability in wind uplift capacity

results for the “aged” ccSPF-retrofitted panels.

• Nail selection (6d common versus 8d ring shank) did not appear to have an effect on

the uplift capacity of the ½” thick OSB retrofitted roof panels. The uplift capacity may

be increased by using thicker sheathing panels or selecting a different sheathing

material (i.e. plywood).

10. FUTURE WORK

The experimental work and results presented in this report about using ccSPF as a roof

retrofit technique in high wind areas provide a good start to understanding the behavior

of retrofitted roof sheathing panels. However, to fully understand the behavior and

interaction of the SPF with the roof sheathing panels, several other factors should be

considered. While, the potential is good the following lists potential areas for research:

• Flexural stiffness of roof sheathing – can this affect the uplift capacity of ccSPF

retrofitted panels

• Compatibility of roof sheathing in contact with ccSPF

• Aged performance of ccSPF – long-term durability of ccSPF.

• Analytical design methods for using ccSPF as a structural adhesive

• Relation of uplift capacity to application technique, pattern or foam volume

• Trapped water and moisture content variations of sheathing and wood members

– effect of ccSPF in limiting drainage

• Repairing/removing ccSPF retrofitted panels and roof members

• Effectiveness of ccSPF as a secondary waterproofing layer in roof construction


• Effect of insulation on underside of roof structure – effect of ccSPF insulation

raising the temperature of asphalt roof shingle

• Comparison of ultimate capacity of field-applied vs. laboratory-prepared

specimens roof panels


REFERENCES

AF&PA. (2001). National Design Specification for Wood Construction ANSI/AF&PA

NDS-2001, American Forest and Paper Association, Washington, D.C.

ASCE. (2006). Minimum Design Loads for Buildings and Other Structures (ASCE/SEI Standard 7-05), American Society of Civil Engineers, Reston, VA.

ASTM. (2004). "E 330-02 Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference." Annual Book of ASTM Standards, American Society for Testing and Materials.

Briggs, R. S., Lucas, R. G., and Taylor, Z. T. (2002). "Climate Classification for Building Energy Codes and Standards." Pacific Northwest National Laboratory, downloaded July 26, 2007, from http://www.energycodes.gov/implement/pdfs/climate_paper_review_draft_rev.pdf.

Chui, Y. H., and Craft, S. (2002). "Fastener head pull-through resistance of plywood and oriented strand board." Canadian Journal of Civil Engineering, 29(3), 384-388.

DOE. (2003). "Map of DOE's Proposed Climate Zones." Downloaded from www.energycodes.gov/implement/pdfs/color_map_climate_zones_Mar03.pdf July 26, 2007.

Hendron, R., Farrar-Nagy, S., Anderson, R., Reeves, P., and Hancock, E. (2004). "Thermal performance of unvented attics in hot-dry climates: Results from building America." Journal of Solar Energy Engineering, Transactions of the ASME, 126(2), 732-737.

ICC-ES. (2005). "ESR-1539 - Power-Driven Staples and Nails." ICC Evaluation Service, Inc., Whittier, CA.

Jones, D. T. (1998). "Retrofit Techniques Using Adhesives to Resist Wind Uplift in Wood Roof Systems," MS Thesis, Clemson University, Clemson, SC.

Lstiburek, J. W. (2006). "Understanding attic ventilation." ASHRAE Journal, 48(4), 36-45.

McLain, T. E. (1997). "Design axial withdrawal strength from wood. II. Plain-shank common wire nails." Forest Products Journal, 47(6), 103-109.

NAHB. (1992). "Testing and Adoption of Spray Polyurethane Insulation for Wood Frame Building Construction Phase 2 -- Wall Panel Performance Testing." Prepared for The Society of the Plastics Industry, Inc., Polyurethane Foam Contractors Division by the NAHB Research Center, Upper Marlboro, MD.

http://www.energycodes.gov/implement/pdfs/climate_paper_review_draft_rev.pdf

http://www.energycodes.gov/implement/pdfs/color_map_climate_zones_Mar03.pdf


NAHB. (1996). "Communication between Bob Dewey of NAHB and Mason Knowles of The Society of the Plastics Industry, Inc., Spray Polyurethane Foam Division." National Association of Home Builders.

Rose, W. B. (1995). "Attic construction with sheathing-applied insulation." ASHRAE Transactions, 101, 789-798.

Rose, W. B., and TenWolde, A. (2002). "Venting of attics and cathedral ceilings." ASHRAE Journal, 44(10), 26-33.

Rudd, A. (2005). "Field performance of unvented cathedralized (UC) attics in the USA." Journal of Building Physics, 29(2), 145-169.

TenWolde, A., and Rose, W. B. (1999). "Issues related to venting of attics and cathedral ceilings." ASHRAE Transactions, 105(pt 1), 851-857.


LITERATURE REVIEW OF SEALED AND VENTED ATTICS

In traditional residential construction, attics are constructed with openings in the soffits

and near ridges of roof structures. Building codes suggest attic venting for several

reasons. In hot climates, openings allow venting to occur which allows heated air in the

attic to escape to the exterior, thereby maintaining a cooler attic space. On a typical

summer day in Florida, the roof temperatures can exceed 180º F with attic temperatures

well over 100º F. The high temperatures radiate through the ceiling down to the

occupied space resulting in additional heating load on the HVAC systems. Venting also

reduces moisture accumulation on the underside of the roof sheathing is also listed as a

benefit to venting.

In cold climates, attic ventilation is used to maintain a cold roof temperature, thereby

minimizing the ice dam formation on the roof. If snow accumulates on a warm roof

surface the roof temperature can melt a layer of snow adjacent to the roof. This water

(snow-melt) flows down the roof and refreezes on colder roof overhangs (eaves) area.

The refreezed snow-melt forms ice which dams further water flow causing the ice layer

to build up, adding weight and damaging the roofing materials.

Attic venting can be accomplished by (a) natural convection - with openings in soffits and

vents near the ridge and (b) mechanical methods - using exhaust fans to create the

airflow (see Figure A.1(a)). Vented attics have insulation installed on the attic floor to

provide a thermal barrier between the attic and the conditioned air space below. Batt

insulation or “blown” insulation is typically used for this purpose.


(a) Vented Attic (b) Unvented (Sealed) Attic

Figure A.1 – Vented and Unvented (Sealed) Attic Concepts (from Hendron et al. 2004)

Current building codes prescribe a minimum opening size for attic ventilation, called the

ventilation ratio (ratio of vent opening to attic floor area). Typically the codes prescribe

attic ventilation ratios ranging from 1:150 to 1:600 with a ventilation of 1:300 being the

most common (Lstiburek 2006). Tenwolde and Rose (1999) note that although this

ventilation ratio was first proposed by the Federal Housing Administration in 1942, there

is no supporting research basis for this ratio.

Tenwolde and Rose identified three important parameters in regulating moisture

conditions in cold climates: (1) indoor humidity, (2) ceiling air tightness and air pressure,

and (3) attic ventilation. Although data to support the 1:300 ventilation ratio was

inconclusive, attic ventilation was suggested as a means to regulate moisture conditions

in the attic in cold climates. Because of the increasing complexity and geometry of

residential roof shapes, effective attic ventilation is sometimes improbable in all or part of

the roof (Lstiburek 2006).

A sealed, or unvented, attic, lacks air vents to allow airflow of attic air to the outside (see

Figure A.1(b)). Instead, sealed attics are insulated directly below the roof sheathing and


at the soffits forming a partially “conditioned” air space. Batt insulation or spray applied

foam insulation can be used for this installation. Table A.1 provides a list of advantages

and disadvantages of sealed attics versus vented attics.

Table A.1 – Global Advantages and Disadvantages of Vented and Unvented Attics

Attic Type Advantages Disadvantages

1. Energy transfer through the ductwork is no longer a loss to the exterior (Rose 1995).

2. Freezing of water pipes in the attic is eliminated.

3. Air tightness requirements for the ceiling plane are reduced or eliminated. Unvented

(Sealed) Attic

4. Renovation and rewiring involve no disturbance to the insulation layer.

5. Attic storage is easier since no insulation is placed on the attic floor (Lstiburek 2006).

6. Prevent or minimizes water leakage of water into the building.

7. May prevent roof pressurization and roof blow off

1. Requires greater technical and coordination of construction during installation.

2. More difficult to install insulation on roof than on top of ceiling.

3. Poor detailing at roof to wall corners can create thermal bridges.

4. Insulation likely to conceal roof sheathing damage or moisture.

1. Residential contractors are more familiar with construction methods and sequencing.

2. Relatively easy to inspect roof structure and replace sheathing.

3. Roof structural or moisture damage easy to inspect.

1. Allows water leakage through soffits and ridge vents into the building during high wind events (Lstiburek 2006).

2. Soffit collapse can lead to internal pressurization and roof blow off (2002).

Vented Attic

It has been suggested that one possible advantage to using sealed attics in high wind

zones is that sealing the soffits can prevent or reduce high wind flow into the attic which

can cause attic pressurization and roof blow off (Rose 1995). However, experimental

investigations have not yet determined if this is so. At the same time, it is likely that

similar attic pressurization can occur when a window or door is broken in the home. The

wind design code takes this into consideration through the internal pressure coefficient

for partially enclosed buildings.


Two issues to consider in the choice of sealed versus vented attics is attic moisture

content and roof shingle temperature. Climate is a major factor in determining the need

for attic venting to control moisture content. The climate of the United States can be

divided into five zones separated by arbitrary boundaries, shown in Figure A.2.

Figure A.2 – Traditional U.S. Climate Zone Regions for Energy-Efficient Building Design (2002)

Briggs et al. (2002) proposed a more detailed climate map, reproduced below Figure A.3

that met several qualifications:

• Offer consistent climate materials for all compliance methods and code sections;

• Be technically sound;

• Map to political boundaries;

• Provide a long-term climate classification solution;

• Be generic and neutral; and,

• Offer a more concise set of climate zones and presentation formats.

Using 30 years of weather observations from 237 U.S. weather stations obtained from

the National Climatic Data Center (NCDC), Briggs et al. (Briggs et al. 2002; DOE 2003)

developed a new climate zone map. Three major climate subdivisions are shown on the

map: (a) Moist, (b) Dry, and (c) Marine. Table A.2 briefly describes the different zones

shown in Figure A.3.


Figure A.3 – Map of DOE’s Proposed Climate Zones (Briggs et al. 2002)

Table A.2 – Climate Zone Definitions (2002)

Zone No. Climate Zone Name and Type

Representative U.S. City

1A Very Hot, Humid Miami, FL

1B* Very Hot, Dry --

2A Hot, Humid Gainesville, FL

2B Hot, Dry Phoenix, AZ

3A Warm, Humid Memphis, TN

3B Warm, Dry El Paso, TX

3C Warm, Marine San Francisco, CA

4A Mixed, Humid Baltimore, MD

4B Mixed, Dry Albuquerque, NM

4C Mixed, Marine Salem, OR

5A Cool, Humid Chicago, IL

5B Cool, Dry Boise, ID

5C* Cool, Marine --

6A Cold, Humid Burlington, VT

6B Cold, Dry Helena, MT

7 Very Cold Duluth, MN

8 Sub-artic Fairbanks, AK

*Defined but not used in the United States


The testing of moisture control and attic ventilation was performed in cold climates, and

Rose and Tenwolde (2002) state that “no scientific claims have ever been made that

attic ventilation is needed for moisture control in hot, humid climates.” In fact, in hot,

humid climates attic venting tends to increase moisture levels in attics (Rose and

TenWolde 2002; TenWolde and Rose 1999).

Rudd (2005) observed several different unvented houses in three cities in a hot, humid

environment (Houston, TX – one house, Jacksonville, FL – one house, and Lake City,

FL – two houses). He found that the roofs with sealed attics and netted and blown-in

cellulose insulation and fiberglass insulation under the roof sheathing needed a vapor-

retarding barrier installed directly under the asphalt composition shingles. This was

necessary to prevent the sheathing from absorbing moisture that condensed on the roof

shingles overnight.

Rudd observed that houses without the vapor barrier had higher moisture levels in the

attic during the day and this placed a higher moisture load on the space cooling system

than is necessary even though overnight the moisture content was equalized with the

living space. Attics with open-cell foam insulation also showed lower resistance to

condensation during winter months if the outside air fell below the dew point temperature

of the attic air due to the higher airflow resistance of open-cell foam. Rudd also

observed that in two Lake City, FL, homes that had sealed attics (open-cell, low-density

foam insulation sprayed to the underside of the roof sheathing) the roof sheathing

showed no signs of moisture condensation, mold, discoloration, delamination, or

deterioration. Wood moisture content ranged from 7-16% for the roof sheathing with the

median at 10% and 7-12% for the roof-framing members with the median about 9%,

which fall within normal moisture content ranges for wood construction materials.


Researchers (Lstiburek 2006; Rose and TenWolde 2002) have found that shingle

temperatures installed over unvented attics tend to be about 2-3º F higher than roof

shingles installed over vented attics. This temperature increase is small as compared to

other factors that affect shingle temperature, such as geographic location, the direction a

roof surface faces, and shingle color, which can increase shingle temperature up to 54º

F higher depending on the color.

Observations by Rudd (2005) of attics in hot, humid climates show that summertime

average daily temperatures of roofing materials is nearly equal whether installed over

vented or unvented attics, however the short-term peak temperatures are increased by

about 7º F for roofing installed over unvented attics. TenWolde and Rose (1999) also

believe, due to the lack of strong evidence, that attic ventilation has insignificant to no

relation to shingle durability due to temperature and moisture concerns.


APPENDIX A – DAILY TESTING REPORTS FROM SPF ROOF PANEL TESTING

Failure Load Panel

ID # Config.* Test Date inHg psi psf

Comments/Failure Modes

27 A 4/5 1.24 0.610 88 • Nail heads pulled through OSB at the center wood member.

26 B 4/5 2.24 1.100 158

• Initial failure at one of the first interior wood members by separation of wood member from foam on both sides.

• Foam remained attached to OSB. • Nail heads pulled through OSB.

12 C 4/5 3.57 1.753 252

• Plastic tore at 2.39 inHg (169 psf) so procedure stopped and tear fixed then test was restarted.

• Failure at one of the first interior wood members by splitting at a knot in the wood member.

• This caused the other two interior wood members to fail by separation of the wood members from the foam on each side while the foam remained attached to the OSB.

• Nail heads pulled through OSB.

28 A 4/6 0.98 0.483 70 • Nail heads pulled through the OSB at the center wood member.

22 B 4/6 2.12 1.041 150

• Evidence of separation of foam from both the wood member and sheathing near end of one of the first interior wood members.

• Failure at the same interior wood member by separation of wood member from foam on one side and separation of foam from sheathing on the other end where it was observed before testing leaving a significant amount of foam attached to the wood member.


2 C 4/6 4.03 1.979 285

• Failure first occurred at the center wood member by separation of wood member from foam on one side and separation of the foam from the OSB on the other side leaving a significant amount of foam attached to the wood member.

• One of the adjacent trusses failed in a similar manner as the center truss.


29 A 4/6 1.42 0.697 100

• On one of the first interior wood members, the three center nail heads pulled through the OSB while the two nails near the ends of the wood member remained so the OSB was still attached to the wood member.


Failure Load Panel



24 B 4/6 2.33 1.041 158

• Observed initial separation of foam from exterior wood member at 1.91 inHg (135 psf).

• Failure occurred at center wood member by separation of foam from wood member.

• Nail heads pulled through sheathing.

3 C 4/6 3.78 1.857 267

• Nail heads were removed from all nails using a grinding wheel.

• One of the exterior wood members split at a knot.

• The adjacent interior wood member then failed by separating from the foam on both sides.

30 A 4/18 0.65 0.319 46

• On one of the first interior wood members, the three center nail heads pulled through the OSB while the two nails near the ends of the wood member remained so the OSB was still attached to the wood member.

1 C 4/18 3.37 1.655 238

• The center wood member separated from the foam on one side and the foam separated from the OSB on the other side.

• An adjacent wood member then failed in the same manner.

• Nail heads pulled through the OSB.

19 B 4/20 2.18 1.071 154

• Center truss separated from the foam on both sides.

• An adjacent wood member then failed in the same manner.

• Nail heads pulled through the OSB.

6 C 4/20 2.55 1.252 180

• Center wood member split at a knot. • An adjacent wood member then failed by

separating from the foam on one side and the foam separating from the sheathing on the other side.


13 C 4/20 N/A N/A N/A

• Panel was tested but pump reached capacity at 3.00 inHg (212 psf) without panel failure.

• Retested at a later date (7/20) when a new pump was ordered.

31 A 4/21 1.2 0.589 85

• Three interior nail heads pulled through OSB on center wood member.

• Similar nail head pull through on both adjacent wood members.

32 A 4/21 1.2 0.589 85

• Nail heads pulled through OSB on center wood member.

• An adjacent wood member then pulled nails through OSB.


Failure Load Panel



21 B 4/21 2.3 1.130 163

• Center wood member separated on both sides from the foam which remained in place on the OSB.

• The two adjacent wood members then failed in a similar manner.


18 B 4/21 2.72 1.336 192

• One of the first interior wood members separated on both sides from the foam which remained in place on the OSB.

• The other two interior wood members then failed in a similar manner.


17 B 4/21 2.53 1.243 179




16 B 4/21 1.5 0.737 106




15 B 4/21 1.5 0.737 106



14 B 4/21 2.38 1.169 168

• Observed initial separation of foam from the OSB on one of the first interior wood members prior to testing.

• Failure occurred first at center wood member by separation of the foam from both sides of the wood member.

• The two adjacent wood members then failed in a similar manner.


20 B 4/21 2.37 1.164 168




33 A 5/14 1.01 0.496 71

• Nail heads pulled through OSB on one of the first interior wood members.

• The center wood member then failed in a similar manner.

34 A 5/14 1.27 0.624 90 • Nail heads pulled through OSB on one of the first interior wood members.


Failure Load Panel



36 A 5/14 1 0.491 71

• Nail heads pulled through OSB on one of the first interior wood members.

• Only the three center nails pulled through the wood member.

23 B 5/14 1.91 0.938 135




25 B 5/14 2.4 1.179 170




1A A 7/18 1.06 0.521 75 • Nails pulled out of the center and one of

the adjacent wood members. The nails remained in the OSB.

1B B 7/18 2.75 1.351 194

• The center and one of the adjacent wood members separated from the foam on both sides of the wood member.

• Nails pulled out of the wood members and remained in the OSB.

1C C 7/18 4 1.965 283

• Center wood member split at a knot about 1 ft from one end.

• The other two interior wood members separated from the foam.

• Nails pulled out of the wood members that failed and remained in the OSB.

2A A 7/18 1.49 0.732 105 • Nails pulled out of all three interior wood members and remained in the OSB.

2B B 7/18 2.52 1.238 178

• One of the first interior wood members failed by separating from the foam on both sides of the member, but the member was still attached to the panel.

• Nails pulled out of this member as well and remained in the OSB.


Failure Load Panel



2C C 7/18 3.48 1.709 246

• The center wood member and one of the adjacent members separated from the foam on one side and the foam separated from the OSB on the other side (~7-8 in.).

• On the other interior wood member, the foam separated from the OSB (~7-8 in.) on both sides of the member.

• Nails pulled out of all three wood members as well and remained in the OSB except for one nail each on both the center and one adjacent wood member at the end of the member which pulled through the OSB.

3A A 7/18 1.01 0.496 71 • Nails pulled out of the center and one

adjacent wood member and remained in the OSB.

3B B 7/18 2.52 1.238 178

• The center wood member and one of the adjacent wood members separated from the foam on one side and on the other side there the foam separated from the OSB and remained attached to the wood members.

• There was little to no residual foam left on the wood members where the foam separated from the members.

• Nails pulled out of these members and remained in the OSB.

3C C 7/19 2.83 1.390 200

• This specimen had a little thinner application of the full foam than the other specimens (approximately 2.5-3.0 in.).

• The center wood member separated from the foam on one side with significant foam residue remaining on the member (upper half of the 3.5 in. dimension). On the other side, the foam separated from the OSB (~6-8 in.).

• One of the other interior wood members split at a knot approximately 12 in. from one end.

• The other interior wood member separated on one side some from the foam at one end but not completely along the whole length of the member. A crack was observed that cut diagonally across the foam out to about 10 in. from the wood member. On the other side there was noticeable separation of the foam from the OSB but the board remained firmly attached at the other end to the panel.

• Nails pulled out of the two members that failed completely and remained in the OSB.


Failure Load Panel



4A A 7/19 1.08 0.530 76 • Nails pulled out of the three interior wood members and remained in the OSB.

4B B 7/19 2.07 1.017 146

• The center wood member separated from the foam on one side completely with little to no foam residue remaining on the member. On the other side, 2/3 of the foam separated from both the wood member and the OSB and on the other 1/3 of the member, the foam separated from only the OSB and remained attached to the member.

• On one of the adjacent wood members separated from the foam on one side completely with little to no foam residue remaining on the member. On the other side, 1/3 of the foam separated from both the wood member and the OSB and on the other 2/3 of the member, the foam separated from only the OSB and remained attached to the member.

• The other interior wood member showed signs of foam separation from the OSB but the member was still firmly attached to the panel.


4C C 7/19 3.59 1.763 254

• The center and one adjacent wood member separated from the foam on one side and approximately 6 in. of foam was separated from the OSB on the other side but the boards remained attached to the panel.

• Nails pulled out of these members and remained in the OSB.

5A A 7/19 0.66 0.324 47

• Nails pulled out slowly from the center and one adjacent wood member.

• On the center wood member, one of the end nails actually pulled through the OSB.


Failure Load Panel



5B B 7/19 2.51 1.233 178

• The center wood member separated from the foam on one side with little to no foam residue remaining on the member. On the other side, half of the wood member separated from the foam and on the other half the foam separated from both the wood member and the OSB (~6 in.).

• On one of the adjacent wood members, the foam separated from the wood member on both sides except ~6 in. at one end on one side where the foam separated from the OSB. There was little to no foam residue left on the wood member.

• On the other interior wood member, one side completely separated from the foam and on the other side the foam separated from the OSB along most of the length even though the board remained attached to the panel.


5C C 7/19 3.8 1.866 269

• The center wood member separated from the foam on both sides along approximately 2/3 of the length and the foam separated from the OSB and remained attached to the wood member along the other 1/3 of the length. Little to no foam remained on the wood member on the bottom half of the 3.5 in. dimension and significant residue remained on the upper half.

• On both of the other interior wood members, the foam separated from the members on one side and from the OSB on the other side (~7-8 in.). On one of the members, there was significant foam residue remaining on about half of its length and on the other little to no foam residue remained along the entire length of the member.


7 C 7/19 2.53 1.243 179

• One of the first interior wood members had foam remaining on both sides of the member but separated from the OSB on both sides.

• The nail heads pulled through the OSB.


Failure Load Panel



5 C 7/19 3.4 1.670 240

• A significant bow in the panel was observed (deflections at the ends were 0.75-0.875 in.).

• The center wood member and one of the adjacent members separated from the foam on one side and 7-8 in. of foam separated from the OSB on the other side and remained intact on the member.

• The wood member did not have much if any foam residue left on the wood member itself on the one side that the foam separated.


11 C 7/20 3.36 1.650 238


• The center wood member separated from the foam on one side (through observation of a large crack in the foam along the wood member) and a noticeable separation from the OSB on the other side of the wood member (~5”) even though the board did not separate from the panel.

• One of the adjacent wood members exhibited the same failures as the center member except the separation from the OSB was about 10 in.


13 C 7/20 3.58 1.758 253

• Retested from earlier date (4/20) after new pump ordered.


• The center and one of the adjacent wood members separated from the foam on one side with varying amounts of foam residue remaining although the top half of the 3.5 in. dimension seemed to consistently have more. On the other side, the foam separated from the OSB (~5 in. except near one end which was about 10 in.).

• The other interior wood member split at a knot about 16 in. from one end.



Failure Load Panel



9 C 7/20 1.97 0.968 139


• One of the first interior trusses was twisted significantly (approximately at a 60º angle from horizontal) prior to testing. All of the nail heads had pulled though most of the OSB as well. There appeared to be no separation of the foam from the wood member, though, prior to testing. This wood member separated from the foam on one side but the other side had a significant amount of foam still attached even though the foam did not separate from the OSB.

• The center and other interior wood members separated from the foam on one side and the foam separated from the OSB on the other side of the wood member (~4-6 in.).


8 C 7/20 3.81 1.871 269


• The center wood member and one adjacent wood member separated from the foam on one side with little to no foam residue remaining especially on the bottom half of the 3.5 in. dimension. The foam separated from the OSB on the other side (~4-6 in. on the center member and ~5-12 in. on the other member).

• The other interior wood member split at a knot approximately 12 in. from one end.



APPENDIX B – INSULSTAR® BROCHURE

The following brochure is for the spray-applied polyurethane foam (ccSPF) product used

in the experimental testing outlined in this report. The Insulstar® foam is manufactured

by NCFI (see Section 4.3).

wind uplift behavior of wood roof sheathing panels ... · wind uplift behavior of wood roof...

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