Walls That Work: Detailing for Performance
Mary Uher August 27, 2014
“The Wood Products Council” is a Registered Provider with The American
Institute of Architects Continuing Education Systems (AIA/CES), Provider #G516.
Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or the Softwood Lumber Board.
Course Description
With wall systems serving so many functions in a building, they can be a challenge to effectively design. As a part of the structural and thermal envelopes, wood-frame walls are vital to building performance. Structural design must be balanced with the need for door and window openings and, at the same time, detailed to limit water and air infiltration. This program focuses on how to maximize wall performance while reducing cost through a combination of new design methods and time-tested details.
Learning Objectives
1. Understand load path continuity and shear wall performance including design methodologies for shear walls.
2. Apply moisture control methods for wood-framed wall systems to maximize their performance in the building envelope.
3. Identify installation considerations that may affect performance and determine how to address these issues proactively as part of the design.
4. Recognize how wood wall systems allow flexibility to adapt to future changes in owner or occupant needs.
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
IBC 2012 1604.4 “Any system of method of construction to be used shall be based on a rational analysis in accordance with well established principles of mechanics. Such analysis shall result in a system that provides a complete load path capable of transferring loads from their point of origin to the load-resisting elements.”
Vertical Load Path Lateral Load Path
Load Path
1. Ridge Beam
2. Post
3. Header
4. Jack Studs
5. Sill Plate
6. Foundation
7. Ground
Load Path
Vertical (Gravity) Load Path Issues Load Load Load
Load Path
Lateral (Sideways) Load Path Issues Load Load Load
Shear W
all Shear W
all
Resisted by shear walls
Load Path Continuity
Resisted by Shear Walls
Racking
Resisted by Anchors
Base Shear
Resisted by Hold Downs & Dead Load
Overturning
Effects of Lateral Forces
Load Path Continuity
Racking
Load Path Continuity
Base Shear
Load Path Continuity 2003 Missouri Tornado
Overturning
Load Path Continuity
Incomplete Load Path – Connections Are Key!
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
Wall Framing: Interior Wall Intersection Options
Ladder Junction Double top plate Interior wall 2x ladder blocking at 24"o.c.
Install blocking with wide face vertical for maximum backing to wall finish and for maximum
insulation in exterior walls.
Wall Framing: Interior Wall Intersection Options
Junction for Continuous Drywall Application
Drywall Interior stud set in 3/4 inch (or more) from exterior wall studs
Detail courtesy of NAHB Research Center
Double top plate
Wall Framing: Three-stud Corners
Insulated Three-stud Corner (California Corner) Difficult to insulate
Traditional Corner
Wall Framing: Two-stud Corners
Corner stud 2x Ladder Blocking at 24"o.c. or Drywall Clips
2x Ladder Blocking at 24"o.c. or Drywall Clips
Wall Framing: Wall Sheathing Installation
! Fasten panels as recommended with 8d nails
! 6" o.c. at all panel edges ! 12" o.c. in the field
! Space panels 1/8" at all panel ends and edges
! Use 7/16 or 15/32 category panels, typically
! Some OSB panels alter strength-axis orientation to allow vertical placement with strength axis across studs
Recommendations for sheathing installation
! Sized for 8, 9, 10 ft. walls
! Eliminates blocking
! Easy to inspect
! Less air infiltration
! More direct uplift and lateral load-path
Oversize Wall Sheathing
Using WSP for Combined Shear and Uplift
! Resist combined uplift and shear
! Lower Cost ! Reduced
Construction Time
Reference: APA SR-101 Design for Combined Shear and Uplift from Wind
Combined Shear and Uplift
Nail pattern at each stud
Uplift Nailing
Lumber ½” space
WSP Tension Splice
Nail pattern at rim joist Transfer Tension
with Studs
Tension Splice at Rim Joist
Wall Framing: Continuous Sheathing
0
2000
4000
6000
8000
10000
12000
0 0.5 1 1.5 2 2.5 3
Load
(lbf
)
Displacement (in.)
3d5b6b 100%2d
2,000 lbf
4,000 lbf
8,000 lbf
10,000 lbf
Diagonal bracing resists 31% of WSP load
WSP wall bracing – Base case
CS-WSP resists 88% more load than WSP bracing
CS-PF resists 174% more load than WSP bracing
6,000 lbf
APA Full-Scale 3D Wall Bracing Tests, Form T2007-73
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
Segmented 1. Aspect Ratio for
seismic 2:1 2. Aspect ratio up to
3.5:1, if allowable shear is reduced by 2w/h
SDPWS 4.3.5.1
Force Transfer 1. Code does not
provide guidance for this method
2. Different approaches using rational analysis are used
SDPWS 4.3.5.2
Perforated 1. Code provides
specific requirements
2. The capacity is determined based on empirical equations and tables
SDPWS 4.3.5.3
Shearwall Design Methods
Shear Wall Design
Specific nail size and spacing requirements
APA wood structural panels of specific grade and thickness Specific
stud species
Anchor bolts
Hold-down anchors
V
H H H v v
H
SDPWS 4.3.5.1 ! Only full height
segments are considered
! Max aspect ratio ! 2:1 – for seismic* ! 3.5:1 – for wind
Aspect ratio applies to full height segment
Segmented (Traditional) Wood Shear Walls
Shear Wall With Openings Force Transfer Around Openings
SDPWS 4.3.5.2 ! Shear around
openings accounted for by strapping or framing based on a “rational analysis”
! H/w ratio defined by wall pier
Aspect ratio applies to wall pier segment
H H v
WALL PIER
V
! Hold-downs only at ends ! Extra calculations and added construction details (connections, strapping, & blocking)
! Uses traditional design values
Shear Wall With Openings Force Transfer Around Openings
H H v
WALL PIER
V
Shear Wall With Opening – Perforated Shear Wall
SDPWS 4.3.5.3 ! Openings accounted for
by empirical adjustment factor
! Hold-downs only at ends ! Uplift between hold
downs, t, at full height segments is required
H H v t
Aspect ratio applies to full height segment
V
Shear Capacity Adjustment
Equation for Perforated Shearwalls
Alternative to tabulated values of Co: Equations 4.3-5 and 4.3-6, 2008 SDPWS ! Allows more efficient perforated shear wall designs
! Actual area of openings ! Tabulated values are based on maximum opening
size ! Example: 1 door & 2 windows ! Table assumes windows are same height as door
! Takes away panel shear area
Shear Capacity Adjustment
Equation for Perforated Shearwalls
Tabulated Shear Capacity Adjustment Factors(Co)
Wind v. Seismic Shear Walls
Wind Design: ! Gypsum strength at wall interior can be added
! 3.5:1 max. aspect ratio for WSP, 2:1 for gypsum
Seismic Design: ! Requires 3x framing more often (SDC D-F)
! 2:1 max. aspect ratio without penalty ! 3.5:1 permitted with penalty (2w/h)
Suggested References
Site-Built Portal Frame Bracing Methods
APA Report TT-100
Portal Frame with Holdowns
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
Designing for Durability: High Wind
Reference: APA Report M310
Roof Sheathing Attachment Gable end connections Cladding attachment
Roof to wall connection
Wall to wall continuity
Wall sheathing attachment Wall sheathing continuity
Wall connection to sill plate
Sill plate anchorage
Gable-end Framing Hurricane Charley
Photo Credit: US Department of Housing and Urban Development
Gable-end Framing
Tie gable end walls back to the structure Gable end truss top chord
Tension-tie strap, attach with (8) 10d common nails, each end of strap
Roof Trusses
(3) 10d Common nails (typical)
2" x 4" continuous lateral brace @ 6' on center. Lateral brace sized to extend from end wall to over 3 interior trusses plus 6".
2x4 flatwise blocking between truss bottom chords
Gable end truss bottom chord
Components and Cladding Loads
Reference: ASCE 7-10 Chapter 30
Components and Cladding Loads
Reference: Requirements for Wall Coverings and Wind Pressures, APA publication TT-105
APRIL 2011 – NC TORNADOS
2011 - RALEIGH, NC
Flying Debris
Wall Sheathing
Siding fastener
s
Siding attachment at energy efficient corners
Attachment base for utility vents, siding trim, etc.
Nail Base For Siding
WSP Sheathing As A Nail Base
Plywood or OSB
Performance Category
Ring Shank Nails (Dia.)
Wood Screws (Gauge)
Smooth Shank and Screw Shank (Dia)
.097 .113 .120 .128 .135 #7 #8 #9 .113 .120 .128 .131
7/16 38 45 48 51 53 61 66 72 11 12 13 13
15/23 or 1/2 41 48 51 54 57 65 71 77 12 13 13 14
19/32 or 5/8 52 61 64 69 73 85 90 97 15 16 17 17
Withdrawal Load (Pounds)1
See APA TT-109 for footnotes and complete table
Reference: APA TT-109
Construction Tips for Building
Moisture Resistant Houses
Understanding Mold & Moisture Intrusion
Durability: Moisture Control
Reference: APA Report A500
Prevent Moisture Intrusion
Four D's of Wall Design
3. Drying
4. Durable
1. Deflection
2. Drainage
Layers of Protection
Layers of Protection
Proper Building Wrap Installation Details*
Tape all tears
12" overlap at corner and vertical joints
Cut and wrap at openings
Tape all joints with air-barrier tape
3" overlap at foundation
Wood structural panel
Overlap horizontal joints 6"-12"
Proper fasteners
* Consult building wrap manufacturer for installation details
BBH – Walls, Page 9
Prevent Moisture Intrusion
Improper water management
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
Meeting Energy Codes Burden is on the builder to produce structures that are: 1. Cost-effective to build 2. Strong and safe 3. Energy efficient
Balancing Cost, Structure and Energy
Whole Building Design
Tips for Sealing Building Envelope
Seal Thoroughly The building envelope separates the interior
conditioned air spaces from the unconditioned
air spaces
Conditioned space
Crawlspace - Unconditioned
Attic - Unconditioned
Whole Building Design
In new construction, the walls of a structure present a great opportunity to prevent energy loss
Meeting Energy Codes with Prescriptive Assemblies
! New joint publication
between ICC and APA
! Advanced Framing options
for meeting R20 or R13+5
insulation values
Reference: APA Report P320
Meeting Energy Codes with Prescriptive Assemblies
Headers thermal path (4%) Studs and plates thermal path (21%) Cavity insulation thermal path (75%)
4%
75%
21%
Average R-Values for Wood and Steel Framed Walls
0 2 4 6 8
10 12 14 16 18
2x4 @ 16" 2x6 @ 16"
10.8
16.2
6.6 8.8
11.6 13.8
Wood with WSP Steel with WSP Steel with WSP + R5 Foam Wall configurations based on stud size and spacing using same level of cavity
insulation. Values developed from a study by the NAHB Research Center (RP02-9)
Walls That Work: Detailing For Performance
! Load Path ! Framing Considerations ! Shear Walls ! Designing for Durability ! Energy Considerations ! Flexibility in Design
Rough Opening Placement The placement of openings in load-bearing walls and the layout of framing members above openings have significant impact on header sizing for advanced framing.
Minimum required materials to frame rough opening Structure above imposing tributary loads on header Potential increased header size - increased load from structure above Excess materials due to inefficient opening placement
Best Placement
36" wide opening
36" wide opening
36" wide opening
24" wide tributary load
24" wide tributary load
48" wide tributary load
Note: Jack studs may not be required if using wood structural panel headers.
Wall Panels
! Faster construction time ! Less waste ! Ease of assembly
Appearance Flexibility
Ease of Additions
Questions?
Mary Uher (410) 730-9663
This presentation was developed by a third party and is not funded by WoodWorks or the softwood lumber check-off.
This concludes The American Institute of Architects Continuing
Education Systems Course
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