Building Enclosure Design and Moisture Performance

Size: px
Start display at page:

Download "Building Enclosure Design and Moisture Performance"

Transcription

1 WoodWorks Webinar February 12, 2014 Building Enclosure Design and Moisture Performance Sam Glass, Ph.D. USDA Forest Products Laboratory Madison, Wisconsin The Wood Products Council is a Registered Provider with The American 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 AIA members and non-aia members are available upon request. This program 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. Learning Objectives Copyright Materials This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited. At the end of this program, participants will be able to: 1. 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 performance strengths and potential risks. The Wood Products Council 2014

2 Quest for the the perfect wall Control layers Cladding Structure The Perfect Wall by J. Lstiburek Cross laminated laminated timber (CLT) timber Courtesy of Darryl Byle,

3 Courtesy of Darryl Byle, Courtesy of Darryl Byle,

4

5 U.S. CLT Handbook Buildings that endure H ry Gakumonji temple, Japan, 8 th c. Heddal stave church, Norway, early 13 th c.

6 Perfect design? Robust design Cladding Control layers Structure The Perfect Wall by J. Lstiburek Perfect execution on the execution the construction site? Perfect building operation and maintenance? How robust or tolerant is the design? Able to recover from unexpected conditions? 1. Recognize hazards that cause cause moisture damage 2. Minimize risk of wetting Design principles and control layers 3. Maximize drying potential Courtesy of Steve Easley Courtesy of Steve Easley

7 Hazards Rain water intrusion Risky roof design Flashing errors (windows, doors, deck ledgers, roof wall intersections) Reservoir claddings not adequately separated from structural sheathing Untreated wood below grade Ice dams Unusually high indoor humidity levels y Damp foundations Construction moisture Outdoor environment Solar radiation Wind Rain, snow Ground water Loads Indoor environment Heat Water vapor Air pressure differences Drivers Liquid water flow Gravity Capillary action Momentum (wind driven) Air pressure Vapor transfer by air flow Air pressure difference Vapor diffusion Vapor pressure difference

8 ASHRAE/DOE/IECC climate zones Moisture loads precipitation Typical annual values Wind driven driven rainrain Horizontal surface Vertical surface 20 inches 100 lb/ft 2 40 inches 200 lb/ft lb/ft2 60 inches 300 lb/ft 2 Depends on Climate Wall orientation Building geometry Exposure Boston New Orleans Seattle

9 Moisture loads winter vapor flow Outdoors cold Typical seasonal values for cold climate Vapor carried by air leakage Indoors + warm Vapor diffusion (assuming 1 perm vapor retarder) Outdoors cold low V.P. 1 lb/ft lb/ft 2 Depends on Indoor humidity levels Leakage paths Pressure difference Indoors warm high V.P. Depends on Indoor humidity levels Vapor permeance Solar driven driven inward diffusioninward diffusion Reservoir cladding Brick veneer Stone veneer Stucco Cement board, etc. Wetted by rain Later warmed by solar radiation radiation Strong drive for inward vapor diffusion Avoid impermeable interior layers Polyethylene Vinyl wall covering Moisture storage capacity of woodstorage of Amount of moisture in 1 ft 3 at 50% RH: Air lb XPS lb Gypsum. 02lb 0.2 lb Wood.. 2 lb Benefits of storage capacity storage Wood can store moisture when humidity rises humidity rises and give it off when humidity drops Buffering reduces humidity peaks and troughsreduces and troughs Analogous to thermal mass Lowers risk of moisture damage Wood frame wall with plywood/osb py sheathing has much greater buffering capacity than steel stud wall with gypsum sheathing g

10 oisture co ontent (%) Equ uilibrium m Thresholds for damage damage Relative humidity (%) Decay Corrosion of embedded fasteners Mold growth Nutrient source Oxygen Suitable temperature Available moisture Mold growth Surface RH above 80% near room temperature (higher surface RH necessary at lower temp) Time for initiation of growth depends on moisture and temperature conditions Bulk Water Management Design principles p Deflection Drainage Water shedding surface Water resistive barrier Drying Durable materials Rain Control in Buildings by J. Straube J Image courtesy of APA,

11 Roof overhangsoverhangs Reduce wind driven rain load on wallsrain on Data source: Survey of building envelope failures in the coastal y f g p f climate of British Columbia, Morrison Hershfield, 1996 Drained/ventilated claddings Improved water management: Drainage Capillary break Pressure moderation Improved drying of drying of cladding and sheathing Reduced inward vapor di drive from reservoir i claddings Further info: All About Rainscreens About by M. Holladay Water resistive resistive barriers Function: drain liquid water that passes the d ate t at t e cladding Many options: Asphalt impregnated building paper Plastic building wraps Fully adhered membranes Liquid applied membranes OSB with integral WRB, taped i t t Rigid foam, taped Further info: All About Water Resistive Barriers by M. Holladay About by Courtesy of Courtesy of APA,

12 Problems with uncontrolled air leakage leakage Air Leakage High energy cost Comfort issues Noise issues i Air quality issues Moisture problems Further info: Air Flow Control in Buildings by J. Straube Wind Stack effect

13 Ventilation fans, air distribution, duct leakage, units parking corridor + elevator shaft Air barrier systems Must be continuous, durable, rigid or supported, rigid or supported able to withstand pressure in both directions Approaches Airtight drywall approach Sealed interior membranes Spray polyurethane foam Taped rigid sheathing Sealed exterior membranes Further info: Air Barrier Association of America Association of America Vapor Diffusion Basic design principles Assess winter and summer vapor drives summer drives Select assembly that is 1. not vulnerable to moisture accumulation t t lti 2. as vapor open as possible to maximize drying potential High concentration low concentration High temperature low temperature

14 Vapor permeancepermeance categories 2012 IBC and IRC wall requirements IRC Vapor impermeable polyethylene aluminum foil 0.1 perm Vapor semi impermeable Kraft faced battfaced vapor retardant paint Vapor semi permeable Vapor permeable 1 perm 10 perms latex paint gypsum board fibrous insulation Class I or II vapor retarders shall be provided II retarders shall provided on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4. Exceptions: 1. Basement walls. 2. Below grade portion of any wall. 3. Construction where moisture or its freezing will re or its ing ill not damage the materials. Climate Zone Marine 4 Class III VR permitted for Vented cladding over wood structural panels Vented cladding over fiberboard Vented cladding over gypsum Insulated sheathing with R value R2.5 over 2 thi ithr l R2 2 4 wall Insulated sheathing with R value R3.75 over 2 6 wall 5 Vented cladding over wood structural panels Vented cladding over fiberboard ddi b d Vented cladding over gypsum Insulated sheathing with R value R5 over 2 4 wall Insulated sheathing with R value R7.5 over 2 6 wall 6 Vented cladding over fiberboard Vented cladding over gypsum Insulated sheathing with R value R7.5 over 2 4 wall Insulated sheathing with R value R11.25 over 2 6 wall 7 and 8 Insulated sheathing with R value R10 over 2 4 wall Insulated sheathing with R value R15 over 2 6 wall Vapor permeancepermeance can depend on RH Vapor permeance 0% Relative Humidity 100% Wood, wood based materials, smart vapor retarders become more permeable as RH increases This allows assemblies to dry more rapidly idl

15 Vapor diffusion in wood in Wood based panels Perm rating at ½ inch thickness Continuous exterior insulation insulation Types of rigid insulation insulation Type R value/inch Vapor permeance p at 1 Foam plastics Expanded polystyrene Extruded polystyrene Polyisocyanurate < 0.1 (foil faced) 2 4(glassfiber 4 (glass fiber faced) faced) Glass fiber, semi rigid board > 10 Mineral fiber, rigid board > 10 Wood fiber insulation board > 10 Image courtesy of FPInnovations,

16 Temperature effect effect ci exterior ci reduces risk of cold weather reduces risk of cold moisture accumulation by warming interior materials such as wood structural sheathingsuch as structural sheathing No ci Indoor temp Sheathing temp Outdoor temp ci Dew point calculations caveats Only steady state vapor diffusion Do NOT include Wind driven driven rainrain Liquid water movement Air movement Effects of sun and night sky radiation Moisture storage RH dependent vapor permeance More than one dimension Vapor permeancepermeance effects ci Vapor tight tight exterior ci Impedes outward drying Reduces inward vapor drive from reservoir drive reservoir claddings Vapor open exterior ciopen exterior Does not impede outward drying May be vulnerable to inward vapor drive from bl d i reservoir cladding; select WRB with appropriate vapor resistanceresistance Drying in both directions Ventilated cladding Vapor open ci p Vapor open WRB Gypsum board/latex paint paint Plywood/OSB Joni Mitchell, Water and Walls by J. Lstiburek

17 Drying outward Drying inwardinward Ventilated cladding Gypsum board Reservoir cladding Gypsum board/latex paint t Vapor open ci Vapor retarder Vapor tight ci ih i Plywood/OSB Vapor open WRB p Plywood/OSB Avoid double vapor retardersdouble vapor retarders Cladding attachment with ciattachment ci Cladding Vapor tight ci ih i Gypsum board/latex paint t Vapor retarder Furring strips/long screws screws Low thermal conductivity spacers Thermally isolated metal brackets l lb Plywood/OSB Macbeth Does Vapor Barriers by J. Lstiburek

18 Summary: key points for moisture design moisture Minimize rain penetration Roof overhangs, rainscreen cladding where needed ldd Proper detailing of WRB, flashing at interfaces Minimize air leakage moisture accumulation Continuous air barrier system 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 cithickness exterior 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 information Water in Buildings: An Architect s Guide to Moisture and Mold, William Rose Water Management Guide, Joseph Lstiburek High Performance Enclosures, John Straube Building Science for Building Enclosures, John Straube and Eric Burnett Designing the Exterior Wall, Linda Brock ASTM Manual, Moisture Control in Buildings: The Manual Moisture in The Key Factor in Mold Prevention The JLC Guide to Moisture Control epa.gov/iaq energy efficient building enclosures.pdf

19 basc.pnnl.gov fpl.fs.fed.us Questions? This concludes The American Institute of Architects Continuing Education Systems Course Sam Glass USDA F t P d t L USDA Forest Products Lab svglass@fs.fed.us