WoodWorks Webinar – February 12, 2014

Building Enclosure 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 2014© The Wood Products Council 2014

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.

www.nibs.org Quest for the “perfect wall”Quest for the perfect wallControl layers

Cladding Structure

The Perfect Wall by J. Lstiburekwww.buildingscience.com

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

Courtesy of Darryl Byle, www.crosslamsolutions.com

Courtesy of Darryl Byle, www.crosslamsolutions.com

Courtesy of Darryl Byle, www.crosslamsolutions.com

U S CLT HandbookU.S. CLT Handbook

www.masstimber.com

Buildings 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

Robust designRobust design

1 Recognize hazards that cause1. Recognize hazards that causemoisture damage

2 Minimize risk of wetting2. Minimize risk of wettingDesign principles and control layers

3. Maximize drying potential

Courtesy of Steve Easley

Courtesy of Steve Easley

HazardsHazards

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

• Reservoir claddings not adequately separated fromstructural sheathing

• Untreated wood below grade• Untreated wood below grade• Ice dams• Unusually high indoor humidity levelsy g y• Damp foundations• Construction moisture

LoadsLoads

Indoor environmentOutdoor environment

Rain, snow

HeatSolar radiation

Heat

WindAir pressure differences

Water vapor

Ground water

Air pressure differences

DriversDrivers

• Liquid water flowLiquid water flow– GravityC ill ti– Capillary action

–Momentum (wind driven)– Air pressure

• Vapor transfer by air flow– Air pressure difference

• Vapor diffusionV diff– Vapor pressure difference

ASHRAE/DOE/IECC climate zonesASHRAE/DOE/IECC climate zones

Moisture loads – precipitationMoisture loads precipitation

Horizontal surface Vertical surface

Typical annual values

Horizontal surface Vertical surface

20 inches 100 lb/ft2

40 inches 200 lb/ft2

60 inches 300 lb/ft2

50 100 lb/ft2

Depends on60 inches 300 lb/ft p• Climate• Wall orientation• Building geometry• Exposure

Wind driven rainWind driven rain

SeattleBoston New Orleans

Moisture loads – winter vapor flowMoisture loads winter vapor flowTypical seasonal values for cold climate

Vapor diffusion(assuming 1 perm vapor retarder)

Outdoors Indoors

Vapor carried by air leakage

Outdoors Indoors–cold

+warm

Outdoorscold

low V.P.

Indoorswarmhigh V.P.

1 lb/f 2 21 lb/ft2 0.1 lb/ft2

Depends on• Indoor humidity levels

Depends on• Indoor humidity levels

• Leakage paths• Pressure difference

• Vapor permeance

Solar driven inward diffusionSolar driven inward diffusion

• Reservoir cladding• Brick veneer• Stone veneer

St• Stucco• Cement board, etc.

• Wetted by rain• Later warmed by solar radiation• Later warmed by solar radiation• Strong drive for inward vapor

diffusion• Avoid impermeable interior layersp y

• Polyethylene• Vinyl wall covering

Moisture storage capacity of woodMoisture storage capacity of wood

Amount of moisture in1 ft3 at 50% RH:

Air………………. 0.0006 lbXPS……………… 0.005 lbG 0 2 lbGypsum………. 0.2 lbWood………….. 2 lb

Benefits of storage capacityBenefits of storage capacity

• Wood can store moisture when humidity risesWood can store moisture when humidity risesand give it off when humidity drops

• Buffering reduces humidity peaks and troughs• Buffering reduces humidity peaks and troughs• Analogous to thermal mass• Lowers risk of moisture damage• Wood frame wall with plywood/OSBp y /sheathing has much greater buffering capacitythan steel stud wall with gypsum sheathinggyp g

Thresholds for damageThresholds for damage30

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 growthMold growth

• Nutrient sourceNutrient source• OxygenS i bl• Suitable temperature

• Available moisture– Surface RH above 80% near room temperature(higher surface RH necessary at lower temp)

• Time for initiation of growth depends onmoisture and temperature conditions

Bulk Water ManagementBulk Water Management Design principles

• Deflection

g p p

Deflection• Drainage

W t h ddi f– Water shedding surface– Water resistive barrier

• Drying• Durable materials

fRain Control in Buildings by J Straube Image courtesy of APA,www.apawood.org

Rain Control in Buildings by J. Straubewww.buildingscience.com

Roof overhangsRoof overhangs

Reduce wind driven rain load on wallsReduce wind driven rain load on walls

Data source: Survey of building envelope failures in the coastaly f g p fclimate of British Columbia, Morrison Hershfield, 1996

Drained/ventilated claddingsDrained/ventilated claddings

• Improved waterpmanagement:– DrainageCapillary break– Capillary break

– Pressure moderation• Improved drying ofImproved drying ofcladding and sheathing

• Reduced inward vapord i f idrive from reservoircladdings

Further info: All About Rainscreens by M HolladayFurther info: All About Rainscreens by M. Holladaywww.greenbuildingadvisor.com

Water resistive barriersWater resistive barriers

• Function: drain liquid water that passes theu ct o : d a qu d ate t at passes t ecladding

• Many options:y p– Asphalt impregnated building paper– Plastic building wraps– Fully adhered membranes– Liquid applied membranesOSB ith i t l WRB t d– OSB with integral WRB, taped

– Rigid foam, tapedFurther info: All About Water Resistive Barriers by M HolladayFurther info: All About Water Resistive Barriers by M. Holladay

www.greenbuildingadvisor.comCourtesy of APACourtesy of APA,www.apawood.org

Air LeakageAir Leakage

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 info: Air Flow Control in Buildings by J. Straubewww.buildingscience.comg

WindWind Stack effectStack effect

Ventilation fans, air distribution, duct leakage, , g

corridor elevator shaft+

+

+

+

+

– –

– –

+– –units

+

+

– ––

parking

+ – ––

– ––

Air barrier systemsAir barrier systems

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

• ApproachesApproaches– Airtight drywall approach– Sealed interior membranesSealed interior membranes– Spray polyurethane foam– Taped rigid sheathingTaped rigid sheathing– Sealed exterior membranes

Further info: Air Barrier Association of AmericaFurther info: Air Barrier Association of Americawww.airbarrier.org

Vapor DiffusionVapor Diffusion

High concentration low concentrationHigh temperature low temperature

Basic design principlesBasic design principles

Assess winter and summer vapor drivesAssess winter and summer vapor drivesSelect assembly that is1 t l bl t i t l ti1. not vulnerable to moisture accumulation2. as vapor open as possible to maximize drying

potentialpotential

Vapor permeance categoriesVapor permeance categories

Vaporimpermeable

Vapor semiimpermeable

Vapor semipermeable

Vaporpermeable

0.1 perm 1 perm 10 perms

polyethylene gypsum boardKraft faced batt latex paintpolyethylenealuminum foil

gypsum boardfibrous insulation

Kraft faced battvapor retardant paint

latex paint

2012 IBC and IRC wall requirements2012 IBC and IRC wall requirements

• Class I or II vapor retarders shall be providedClass I or II vapor retarders shall be providedon the interior side of frame walls in Zones 5,6 7 8 and Marine 46, 7, 8 and Marine 4.– Exceptions:1 Basement walls1. Basement walls.2. Below grade portion of any wall.3 Constr ction here moist re or its free ing ill3. Construction where moisture or its freezing will

not damage the materials.

Climate Zone Class III VR permitted for

Marine 4 Vented cladding over wood structural panelsVented cladding over fiberboardVented cladding over gypsumI l t d h thi ith R l R2 5 2 4 llInsulated sheathing with R value R2.5 over 2 × 4 wallInsulated sheathing with R value R3.75 over 2 × 6 wall

5 Vented cladding over wood structural panelsV t d l ddi fib b dVented cladding over fiberboardVented cladding over gypsumInsulated sheathing with R value R5 over 2 × 4 wallInsulated sheathing with R value R7.5 over 2 × 6 wallg

6 Vented cladding over fiberboardVented cladding over gypsumInsulated sheathing with R value R7.5 over 2 × 4 wallgInsulated sheathing with R value R11.25 over 2 × 6 wall

7 and 8 Insulated sheathing with R value R10 over 2 × 4 wallInsulated sheathing with R value R15 over 2 × 6 wallg

Vapor permeance can depend on RHVapor permeance can depend on RH

VaporVaporpermeance

0% Relative Humidity 100%

• Wood, wood based materials, “smart vapor retarders”become more permeable as RH increasesThi ll bli d idl• This allows assemblies to dry more rapidly

Vapor diffusion in woodVapor diffusion in wood Wood based panelsWood based panelsPerm rating at ½ inch thickness

Continuous exterior insulationContinuous exterior insulation

Image courtesy of FPInnovations,www.fpinnovations.ca

Types of rigid insulationTypes of rigid insulation

Type R value/inch Vapor permeance at 1”yp / p p

Foam plastics

Expanded polystyrene 3.7 – 4.3 2 – 4

Extruded polystyrene 5.0 – 5.6 0.7 – 1.4

Polyisocyanurate 5.0 – 6.0 < 0.1 (foil faced)2 – 4 (glass fiber faced)2 – 4 (glass fiber faced)

Glass fiber, semi rigid board 3.5 – 4.2 > 10

Mineral fiber, rigid board 3.5 – 4.3 > 10

Wood fiber insulation board 2.7 – 4.0 > 10

Temperature effect – ciTemperature effect ci

exterior ci reduces risk of cold weatherexterior ci reduces risk of cold weathermoisture accumulation by warming interiormaterials such as wood structural sheathingmaterials such as wood structural sheathing

ciNo ci

Indoor tempIndoor temp

Outdoor temp

Sheathing temp

p

Dew point calculations – caveatsDew point calculations caveats

• Only steady state vapor diffusionOnly steady state vapor diffusion• Do NOT include

– Wind driven rainWind driven rain– Liquid water movement– Air movementAir movement– Effects of sun and night sky radiation– Moisture storageg– RH dependent vapor permeance– More than one dimension

Vapor permeance effects – ciVapor permeance effects ci

• Vapor tight exterior ciVapor tight exterior ci– Impedes outward dryingReduces inward vapor drive from reservoir– Reduces inward vapor drive from reservoircladdings

• Vapor open exterior ci• Vapor open exterior ci– Does not impede outward dryingM b l bl t i d d i f– May be vulnerable to inward vapor drive fromreservoir cladding; select WRB with appropriatevapor resistancevapor resistance

Drying in both directionsDrying in both directions

Ventilated cladding Gypsum board/latex paintVentilated cladding Gypsum board/latex paint

Plywood/OSBVapor open ci

Vapor open WRB

yp p

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

Drying outwardDrying outward

Ventilated cladding Gypsum board

Vapor open WRB Plywood/OSB

Vapor retarderVapor open ci

p p y

Drying inwardDrying inward

G b d/l t i tR i l ddi

i h i

Gypsum board/latex paint

l d/

Reservoir cladding

Vapor tight ci Plywood/OSB

Avoid double vapor retardersAvoid double vapor retarders

G b d/l t i tCl ddi

i h i

Gypsum board/latex paintCladding

dVapor tight ci

Plywood/OSB

Vapor retarder

Plywood/OSB

Macbeth Does Vapor Barriers by J. Lstiburekwww.buildingscience.com

Cladding attachment with ciCladding attachment with ci

• Furring strips/long screwsFurring strips/long screws• Low thermal conductivity spacers

h ll i l d l b k• Thermally isolated metal brackets

Summary: key points for moisture designSummary: key points for moisture design

• Minimize rain penetrationf h l dd h d d– Roof overhangs, rainscreen cladding where needed

– Proper detailing of WRB, flashing at interfaces• Minimize air leakage moisture accumulation

– Continuous air barrier systemContinuous air barrier system– Exterior ci reduces risk

• Minimize solar driven inward moisture from reservoir claddings– Ventilate the cladding– Design assemblies to dry inward

• Manage wintertime vapor diffusion in cold climates– Interior vapor retarder if necessary (smart vapor retarder preferable)– Sufficient thickness of exterior ciSufficient thickness of exterior ci

• Maximize drying potential– Design assemblies to dry in at least one direction appropriate to climate– The most robust designs can dry in both directions

Further informationFurther information

• Water in Buildings: An Architect’s Guide togMoisture and Mold, William Rose

• Water Management Guide, Joseph Lstiburek• High Performance Enclosures, John Straube• Building Science for Building Enclosures, JohnStraube and Eric BurnettStraube and Eric Burnett

• Designing the Exterior Wall, Linda Brock• ASTMManual Moisture Control in Buildings: TheASTMManual,Moisture Control in Buildings: TheKey Factor in Mold Prevention

• The JLC Guide to Moisture Control

http://www.fpinnovations.ca/ResearchProgram/AdvancedBuildingSystem/designing energy efficient building enclosures.pdf

epa.gov/iaq

basc.pnnl.gov fpl.fs.fed.us

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