Minneapolis Wood Solutions Fair – September 17, 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.

National Paint and Varnish Association, 1951

Buildings that endureBuildings that endure

Heddal stave church, Norway, early 13th c.H ry Gakumonji temple, Japan, 8th c. Heddal stave church, Norway, early 13 c.H ry Gakumonji temple, Japan, 8 c.

Carson Mansion, California, 1884Parson Capen House, Massachusetts, 1683

Photo courtesy of National Park Service

Photo courtesy of Carol Clausen

Robust Design vs. Perfect DesignRobust Design vs. Perfect Design

• Perfection on thePerfection on theconstruction site?

• How much control doesa designer have?

• Need to design forgmoisture tolerance

The Perfect Wall by Joe Lstiburekwww.buildingscience.com

Defensive DesignDefensive Design 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)

Photo courtesy of Steve Easley

Photo courtesy of Anton TenWolde

Photo courtesy of Advanced Energy

Photo courtesy of Carol Clausen

HazardsHazards

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

wall intersections)• Reservoir claddings not adequately separated• Reservoir claddings not adequately separated

from structural sheathing• Untreated framing/sheathing below gradeU t eated a g/s eat g be o g ade• Ice dams• Unusually high indoor humidity levelsg• Air leakage• Damp foundations

Special Report: Minnesota’s Rotting Stucco Walls by Martin HolladayEnergy Design Update, May 2006

LoadsLoads

Indoor environmentOutdoor environment

Rain, snow

HeatSolar radiation

Heat

Water vapor

WindAir pressure differences

Ground water

Moisture loads – precipitationMoisture loads precipitationTypical annual values for Twin Cities

Horizontal surface Vertical surface

East facing wall

150 lb/ft2 50 lb/ft2150 lb/ft 50 lb/ft

Depends on• Orientation

B ildi t• Building geometry• Exposure

Moisture loads – vapor flowMoisture loads vapor flowTypical annual values for Twin Cities

Vapor diffusionassuming 1 perm vapor retarder

Air leakage

Outdoors

–cold

Indoors

+warm

Outdoorscold

low pv

Indoorswarmhigh pv

1 lb/ft2 0.1 lb/ft2

Depends onI d h idit l l

Depends onI d / td• Indoor humidity levels

• Leakage paths• Pressure difference

• Indoor/outdoor vapor pressure• Vapor permeance

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

Moisture storage capacity of woodMoisture storage capacity of wood30

20

25

onte

nt (%

)

15

moi

stur

e co

5

10

Equi

libriu

m

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 (%)

Further informationFurther information

www.fpl.fs.fed.us

Defensive DesignDefensive Design

1 Recognize the hazard1. Recognize the hazard2. Understand the defense3 i i i i d i i d i3. Minimize wetting and maximize drying

Exterior water managementExterior water management

• DeflectionDeflection• Drainage

W t h ddi– Water sheddingsurfaceWater resistive– Water resistivebarrier

• Drying• Drying• Durable materials

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

All About Rainscreens by Martin 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

Air Flow Control in Buildings by John Straubewww.buildingscience.com

Stack effectStack effect

Air leakage in foundationsAir leakage in foundationsBasements:• Stack effect in winter can cause buildings to

inhale through the soil, bringing in watervapor, radon, odors

• FPL research demonstration house: 20 40• FPL research demonstration house: 20 40lbs of moisture per day during cold weatherplus high radon levels

• Sub slab ventilation effectively solves theSub slab ventilation effectively solves themoisture issue as well as the radon issue

Crawl spaces:• Wall vented crawl spaces in southeasternp

U.S. conducive to mold growth• Mold spores from crawl space infiltrate into

the living space via air leakage through thefloorfloor

Air leakage in walls and roofsAir leakage in walls and roofsCold climate examples• Wall case study in Montana

Outdoors IndoorsWall case study in Montana

– Highly insulated, tight house (1.2 ACH at 50 Pa)– Moisture content of sheathing measured in 120 locations– Huge variation: most readings <20% but some >40% MC

IR thermography and pressurization/depressurization showed

–cold

+warm

– IR thermography and pressurization/depressurization showedthat air leakage paths corresponded with locations of high MC

• SIP roofs in Alaska– Major moisture accumulation in multi unit residential buildings

f i l k t f l j i tfrom air leakage at roof panel joints

Hot humid climate examples• Negative pressure (wind stack effect exhaust fan)

Outdoors

+Indoors

–• Negative pressure (wind, stack effect, exhaust fan)brings humid outdoor air into wall or roof assembliescooled by air conditioning

• Moldy hotels in Florida

warm cold

y

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

Vapor diffusionVapor diffusion

Principled approach:Principled approach:• Assess the interior and exterior environments• Provide only as much vapor diffusion• Provide only as much vapor diffusion

resistance as necessary• Make the assembly as vapor permeable as• Make the assembly as vapor permeable as

possible to maximize drying capability withoutmaking it vulnerable to moisture accumulationmaking it vulnerable to moisture accumulation

• Need for interior VR may depend on whetherexterior insulation is included in the assemblyexterior insulation is included in the assembly

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 retardersbecome more permeable as RH increases

y

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

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 panels

Variability in OSBVariability in OSB 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

• Consider moisture tolerance

Wood frame examplesWood frame examples

• Strengths/vulnerabilitiesStrengths/vulnerabilities• Vapor management

i i l i• Exterior insulation

Cross laminated timberCross laminated timber

Further informationFurther information

www.masstimber.com www.fpinnovations.ca

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