Wood Solutions Fair – Baltimore – November 14, 2013

Building Envelope Design andMoisture Performance

Sam Glass Ph DSam Glass, Ph.D.USDA Forest Products Laboratory

Madison, Wisconsin,

“Th W d P d t C il” i R i t d P id ith Th“The Wood Products Council” is a Registered Provider with TheAmerican Institute of Architects Continuing Education Systems (AIA/CES).Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members Certificates of Completion for both AIAAIA/CES for AIA members. Certificates of Completion for both AIAmembers and non-AIA members are available upon request.

This program is registered with AIA/CES for continuing professionalThis program is registered with AIA/CES for continuing professionaleducation. 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,y g gdistributing, or dealing in any material or product.

Questions related to specific materials, methods, and services willQuestions related to specific materials, methods, and services willbe addressed at the conclusion of this presentation.

Copyright Materials

This presentation is protected by US and International Copyright laws ReproductionInternational Copyright laws. Reproduction,

distribution, display and use of the presentation without written permission of the speaker is

prohibitedprohibited.

© The Wood Products Council 2013© The Wood Products Council 2013

Learning ObjectivesLearning Objectives

At the end of this program, participants will be able to:

1 Understand the functions of materials used to achieve control of heat air and1. Understand the functions of materials used to achieve control of heat, air, and

moisture in the building envelope.

2. Understand the mechanics of moisture movement in building assemblies.

3. Understand the properties of wood and wood products that relate to heat, air,

and moisture transfer and the conditions that can lead to mold and decay.

4. Evaluate various building envelope designs for moisture performanceg p g p

strengths and potential risks.

Buildings that endureBuildings that endure

H ry Gakumonji temple, Japan, 8th c.

Heddal stave church, Norway, early 13th c.

Perfect design?Perfect design?

• Perfect execution on theControl layers

• Perfect execution on theconstruction site?

• Perfect building operationCladding Structure

• Perfect building operationand maintenance?

• How “robust” orHow robust or“tolerant” is the design?

• Able to recover fromAble to recover fromunexpected conditions?

The Perfect Wall by J. Lstiburekwww.buildingscience.comg

Defensive DesignDefensive Design

National Paint and Varnish Association, 1951

Defensive DrivingDefensive Driving

• R U A Defensive Driver?R U A Defensive Driver?• Collision prevention formula

R i th h d th t lli i– Recognize the hazard that can cause a collision– Understand the defense to avoid the hazard– Act correctly, in time

National Safety Councilwww.SafetyServe.com

Defensive DesignDefensive Design

1 Recognize hazards that can cause moisture1. Recognize hazards that can cause moisturedamage

(Nuisance – health risk – structural damage)(Nuisance – health risk – structural damage)

2. Minimize risk of wetting3. Maximize drying capability

Courtesy of Steve Easley Courtesy of Steve Easley

Courtesy of Steve Easley

HazardsHazards

• Rain water intrusion– Risky roof design– Flashing errors (windows, doors, deck ledgers, roof wall

intersections))• Reservoir claddings not adequately separated from

structural sheathing• Untreated framing/sheathing below grade• Untreated framing/sheathing below grade• Ice dams• Unusually high indoor humidity levelsy g y• Damp foundations• Construction moisture

DriversDrivers

• Liquid water flow• Liquid water flow– Gravity, momentum, air

diffpressure differences

• Capillary action• Vapor transfer by air flow

– air pressure differencep• Vapor diffusion

– vapor pressure difference

LoadsLoads

Indoor environmentOutdoor environment

Rain, snow

HeatSolar radiation

Heat

Water vapor

WindAir pressure differences

Ground water

Moisture loads – precipitationMoisture loads precipitationTypical annual values for Baltimore

Horizontal surface Vertical surface

Northeast facing wall

200 lb/ft2 100 lb/ft2200 lb/ft 100 lb/ft

Depends on• Orientation

B ildi t• Building geometry• Exposure

Moisture loads – vapor flowMoisture loads vapor flowTypical winter values for Baltimore

Vapor diffusionassuming 1 perm vapor retarder

Air leakage

Outdoors

–cold

Indoors

+warm

Outdoorscold

low V.P.

Indoorswarm

high V.P.

1 lb/ft2 0.1 lb/ft2

Depends onI d h idit l l

Depends onI d h idit l l• Indoor humidity levels

• Leakage paths• Pressure difference

• Indoor humidity levels• Vapor permeance

Moisture loads – vapor flowMoisture loads vapor flowTypical summer values for Baltimore

Vapor diffusionAir leakage

Outdoors

+warm

Indoors

–cool

Outdoorswarm

high V.P.

Indoorscool

low V.P.

1 lb/ft2 0.1 lb/ft2

Design walls to dry in both directionsDesign walls to dry in both directions

Further information: Joni Mitchell, Water and Walls by J. Lstiburekwww.buildingscience.com

Moisture storage capacity of woodMoisture storage capacity of wood30

20

25

onte

nt (%

)

15

moi

stur

e co

5

10Eq

uilib

rium

0 20 40 60 80 1000

Relative humidity (%)Relative humidity (%)

Damage functionsDamage functions30

Corrosion ofembedded fasteners

Decay

20

25

onte

nt (%

)

Mold growth

embedded fasteners

15

20

oist

ure

co

10

uilib

rium

m

0

5Equ

0 20 40 60 80 1000

Relative humidity (%)

Mold growth limiting conditionsMold growth limiting conditions Exterior water management

• Deflection

g

Deflection• Drainage

W t h ddi– Water sheddingsurfaceWater resistive– Water resistivebarrier

• Drying• Drying• Durable materials

Courtesy of APA, www.apawood.org

Courtesy of APA, www.apawood.org

Water management risk factorsWater management risk factors

• ClimateClimate– Precipitation

Drying potential– Drying potential

• Building height• Roof overhangs• Type of cladding• Quality of workmanship/detailing

Benefits of drained/ventilated claddingBenefits of drained/ventilated cladding

• Improved waterp o ed atemanagement:– Drainage– Capillary break– Pressure moderation

• Improved drying ofcladding and sheathingR d d i d• Reduced inward vapordrive from reservoircladdingscladdings

Further information: All About Rainscreens by M. Holladaywww.greenbuildingadvisor.com

Problems with uncontrolled air leakageProblems with uncontrolled air leakage

• High energy costHigh energy cost• Comfort issues

i i• Noise issues• Air quality issues• Moisture problems

Further information: Air Flow Control in Buildings by J. Straubewww.buildingscience.com

Stack effect Air barrier systemsAir barrier systems

• Must be continuous, durable, rigid or supported,, , g pp ,able to withstand pressure in both directions

• Approachesh d ll h– Airtight drywall approach

– Sealed polyethylene– Spray polyurethane foamSpray polyurethane foam– Taped rigid sheathing– Exterior membranes

ld• Building wraps• Self adhered membranes• Fluid applied membranes

Further information: Air Barrier Association of Americawww.airbarrier.org

Vapor diffusionVapor diffusion

• Make the assembly as vapor permeable asMake the assembly as vapor permeable aspossible to maximize drying capability withoutmaking it vulnerable to moisture accumulationmaking it vulnerable to moisture accumulation

Vapor permeance categoriesVapor permeance categories

Vaporimpermeable

Vapor semiimpermeable

Vapor semipermeable

Vaporpermeable

0.1 perm

Class I VR

1 perm

Class II VR Class III VR

10 perms

(not considered a VR)

polyethylene building wrapsvapor retardant paint 1” EPSpolyethylenealuminum foil

building wrapsgypsum board

fibrous insulation

vapor retardant paint1” XPS

1 EPS

Vapor permeance can depend on RHVapor permeance can depend on RH

VaporVaporpermeance

0% Relative Humidity 100%

• Solid wood, plywood, OSB, “smart vapor retarders”become more permeable as RH increases

y

become more permeable as RH increases• This allows assemblies to dry more rapidly

Classic wood frame wallClassic wood frame wall

Lap sidingp gFeltPlywoodKraft faced batt insulationG b dGypsum board

Vapor diffusion in woodVapor diffusion in wood

(arb

. uni

ts)

Longitudinal

r per

mea

bilit

y (

Vapo

r

Transverse

Mean relative humidity (%)0 20 40 60 80 100

Softwood tracheidLength: 1/8 inchDiameter: 0.001 inch L

Wood based panelsWood based panelsPerm rating at ½ inch thickness

Effects of exterior insulationEffects of exterior insulation

Courtesy of FPInnovations, www.fpinnovations.ca

Effects of exterior insulationEffects of exterior insulation

1. Thermal effect. e a e ect– exterior insulation reduces risk of cold weather

moisture accumulation by warming materials such asd t t l h thiwood structural sheathing

2. Vapor diffusion effectLow perm exterior foam– Low perm exterior foam

• impedes outward drying• reduces inward vapor drive from moisture reservoir

claddings

– Vapor permeable exterior insulation (rigid mineralwool, wood fiber insulation board) – oppositewool, wood fiber insulation board) opposite

Evaluating design robustnessEvaluating design robustness

• Desired moisture performance:Desired moisture performance:– Minimize vulnerability to rain penetration

Minimize vulnerability to air leakage– Minimize vulnerability to air leakage– Minimize vulnerability to vapor diffusion

M i i d i bilit– Maximize drying capability

Which is more robust?Which is more robust?

Wall A Wall BWall A• Drywall• Latex paint (Class III vapor

Wall B• Drywall• Smart vapor retarderLatex paint (Class III vapor

retarder)• Batt insulation/wood

f

Smart vapor retarder• Batt insulation/wood

framingframing

• Wood structural panel• Permeable WRB

• Wood structural panel• Permeable WRB

L idi• Permeable WRB• Lap siding

• Lap siding

Latex paint: not reliable for interiorlvapor control

• Recent measurements from multiplelabs: vapor permeance of gypsum

30

Dash Line UnFaced Cavity Batts labs: vapor permeance of gypsumboard with two coats latex paint 20perms or greater

• Home Innovation Research Labs teststructure (climate zone 4A) showed

20

25

eCo

nten

tin

% #1 Man Stone

#2 Stucco w/ 2layers

#3 Cedar w/ 3/4"furring

#4 Vinyl Siding

Solid Line Kraft Faced Cavity Batts

structure (climate zone 4A) showedOSB moisture contents around 25%in winter and mold growth

10

15

OSB

Moi

stur

e y g

#5 Brick

#6 Fiber CementSiding

#8 Vinyl Sidingw/2x6

5

Which is more robust?Which is more robust?

Wall C Wall DWall C• Drywall• No VR except interior paint

Wall D• Drywall• No VR except interior paintNo VR except interior paint

• R 13 cavity insulation• Wood structural panel

No VR except interior paint• R 13 cavity insulation• Wood structural panel

• Permeable WRB• R 5 extruded polystyrene

• Permeable WRB• R 5 mineral wool

• Lap siding • Lap siding

www.fpl.fs.fed.us

Cross laminated timber (CLT)Cross laminated timber (CLT)

Courtesy of Darryl Byle, www.crosslamsolutions.comCourtesy of Darryl Byle, www.crosslamsolutions.com

Courtesy of Darryl Byle, www.crosslamsolutions.com

Courtesy of FPInnovations, www.fpinnovations.ca

U.S. CLT Handbook

www.masstimber.com

http://www.fpinnovations.ca/ResearchProgram/AdvancedBuildingSystem/designing energy efficient building enclosures.pdf www.fpl.fs.fed.us

Laboratory research in progressLaboratory research in progressChamber for AAnalytic RResearch on WWall Assemblies exposed to Simulated weatherAssemblies exposed to Simulated weather (CARWASh)

Chamber for Analytic Research on Wall Assembliesd t Si l t d th (CARWASh)exposed to Simulated weather (CARWASh)

Questions?Questions?

This concludes The AmericanInstitute of Architects ContinuingEducation Systems Course

Sam GlassUSDA F t P d t L bUSDA Forest Products Labsvglass@fs.fed.us