Objectives Compare locations in North America Potential for moisture problems Different driving forces Analyze what motivates building codes Read Lstiburek articles for Thursday

Review moisture transport Moisture transport Liquid flow Vapor diffusion Air movement Capillary action What driving force is responsible for each one? What do you need for each transport method?

BSCBSC Approach Divide nation (or world) into “zones” based on hygro-thermal parameters Design building codes and strategies to address the important sources and driving forces Ignore unimportant driving forces Result should be buildings that are climate specific

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Digression What is a heating degree day? Have to define a base (usually 65 °F or 18°C) Subtract average daily temperature from 65 °F and sum over heating season. Ignore days when temperature is above 65 °F Can also do it hourly, different basis, etc.

Very Cold Climate Definition: 9,000 – 12,600 HDD, wide range of precipitation levels What do we know about temperature and vapor pressure differences? What do we know about building construction? What problems are likely?

Strategies for Very Cold Climates Interior vapor retarders, well sealed ~Loose exterior sheathing Tight rigid insulation on exterior of stud walls Great attention paid to air sealing Foundation damp proofing, sealed insulation, capillary break, free draining backfill, site grading HVAC balanced with HRV Conventionally vented attic

Cold Climate Definition: 5,400 < HDD < 9000, wide range of precipitation levels What do we know about temperature and vapor pressure differences? What do we know about building construction? Air conditioning? What problems are likely?

Strategies for Cold Climates Minimal vapor retarders (interior paint) NO polyethylene Tight rigid insulation on exterior of stud walls Limit thermal bridging Attention paid to air sealing (primarily interior) Foundation same as for severe cold: damp proofing, sealed insulation, capillary break, free draining backfill, site grading Slightly different for crawlspace Similar HVAC to very cold, but no HRV

Mixed/Humid Climate Definition: Less than 5,400 HDD, more than 20” of rainfall/year, winter monthly average outdoor temperature drops below 45 °F What do we know about temperature and vapor pressure differences? What do we know about building construction? What problems are likely?

Strategies for Mixed/Humid Climates Exterior weak vapor retarders, thin rigid insulation Great attention paid to interior air sealing SOG – continuous vapor barrier underneath, slab edge insulated. Do not apply impermeable floor covering Similar HVAC to cold climate

Mixed/Dry Climate Definition: Less than 5,400 HDD, less than 20” of rainfall/year, winter monthly average outdoor temperature drops below 45 °F What do we know about temperature and vapor pressure differences? What do we know about building construction? What problems are likely?

Strategies for Mixed/Dry Climates Very similar to mixed/humid Exterior air barrier (typically with stucco) Assembly can be less forgiving Hot/Dry climate is same, but average temp. stays above 45°F Exterior air barrier, don’t insulate slab, building assembly can dry out very easily Rain and groundwater are biggest threats Unvented Attic

Hot-Humid Climates More than 20” of rainfall and one of the following: a 67°F (19.5°C) or higher wet bulb temperature for 3,000 or more hours during the warmest six consecutive months of the year; or a 73°F (23°C) or higher wet bulb temperature for 1,500 or more hours during the warmest six consecutive months of the year. What do we know about temperature and vapor pressure differences? What do we know about building construction? What problems are likely?

Strategies for Hot-Humid Climates Interior and exterior air retarders Walls must be able to dry to the inside No significant vapor retarders Don’t insulate edge of foundation. Why? Unvented attic

Disadvantages? Training construction workers Every strategy involves air retarder system Many strategies require exterior rigid insulation Risk of trying new ideas Defining appropriate zones without defining too many zones Relying on higher quality construction

Disadvantages? Training construction workers Risk of trying new ideas Defining appropriate zones without defining too many zones Relying on higher quality construction Working with building code officials

Objectives Review moisture transport Compare locations in North America Potential for moisture problems Different driving forces Analyze what motivates building codes