Th W d P d t C ilThe WoodProducts Council” i R i t d P id ... Ph DSam Glass, Ph.D. USDA Forest Products Laboratory Madison, Wisconsin “Th W d P d t C ilThe WoodProducts Council”
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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
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
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
– 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
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
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
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 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
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