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Walls and slabs

Building Enclosures 

Similarities of building enclosures for cold climates to cold climate outdoor gear.

Cold climate sports gear serves as a suitable analogy for building enclosures where the sleeping bag represents the insulation, sleeping bag VB liner as a vapor barrier and fabric such as
Gortex as the breathable wind/rain barrier with pit zips as the equivalent to exfiltration.

Wall Insulation Myths

Just because the insulation filling a wall cavity is rated at R20 does not mean the wall is rated at R20. In fact an R20 wall cavity has a total wall R-value between R12 and R14 due to the wood framing. In the thermographic image below, note the darker colors. These are the wood studs that are conducting warm heat to the cold outside. This is called thermal bridging.

Thermal bridging through framing members degrades the overall wall performance with windows and door framing contributing to a significant loss.









Photo credits: Bob Rohr

In cold climates with mixed humidity loads, it is always important to keep the heat in during the winter but the walls must also be able to dry during initial curing cycles and subsequent variable moisture loads during the shoulder and summer seasons.

Air barrier & vapor barrier

Below grade walls: air barriers are not a concern since the concrete is a 100% effective air barrier. However moisture (vapor) barriers have to be properly located to ensure drying of the basement wall during moist periods such as curing times.

Rigid insulation types
Rigid insulation types and characteristics.

NRC-IRC: Building Science for a Cold Climate, dog eared and coffee favorite book. Authored by Hutcheon and Handegord - first published in 1983 it remains today as an authoritative resource.


Walls and slabs for cold climates:
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Above and below grade walls and slabs are one of the prime elements in controlling moisture, heat, sound, short/long wave radiant energy and contaminants such as odors, gases and particulates. Wall framing is a conductive heat path  (heat loss in winter/heat gain in summer) ergo the less framing material the less thermal bridging. In cold climates walls and slabs should be built to encourage drying year round, retaining heat in winter and preventing over heating in the summer (see controlling solar loads).
(see overview of housing performance categories in North America)

This topic is part of our Professional Development curriculum. Several on-line webinars and multiday programs are offered through the year - many are at no cost or available with government subsidies.  Be sure to also check out our new Donate to Educate program.

There are numerous materials and methods to design and construct high performance walls and slabs for cold climates. Below you will find our suggested methods based on research work within the building science community and adapted to reflect low temperature heating and cooling systems.

Basic high performance wall using 5.5" of cellusoe or friction fir with 2" of rigid insulation.

Basic above grade wall assembly vented with an air gap between the siding and the exterior rigid insulation (min. 2"). Rigid insulation is staggered and seams taped to serve as part of the air barrier system. Vapour control is latex paint over drywall (see ADA)  or poly vapor barrier. Minimum R24 wall shown includes 5.5" wall insulation and an allowance for minimal thermal bridging when using high performance framing techniques (see wall insulation myths).

Showing exterior wall detail when using radiant wall heating.

As above except showing radiant wall detail. Rigid insulation added to interior. Grooved tracking boards with heat transfer plates and radiant tube. Finish as required.

Cantelevered floor section for radiant floor heating.

Shown above: cantilevered floor details. Spray foam insulation is ideal in this application to seal and add R value. Second choice would be rigid with fiberglass batt insulation. Seal all potential air passages.  Critical area for all buildings but especially important to buildings conditioned with under floor heating systems

Foundation wall penetrations.

Foundation wall penetrations can be cast during pour or cored afterwards. Seal and insulate all heat, moisture and air passages. Use screened, dampened hoods for rodent, bird and insect control. Flash and caulk hood to prevent moisture penetration.

Foundation wall and grade detail

Basic below grade foundation wall at grade detail. Note the cement board on the exterior. Zone above grade serves as the moisture relief region for the concrete and wood framed wall as such do not seal this area.1 Drainage and moisture membrane fastened to exterior rigid insulation. Air barrier not a concern as concrete is 100% effective. In cold dry climates latex paint on drywall serves as vapor barrier. In other climates provide mechanical dehumidification. Minimum overall R value = R 20

drainage and insulation wall and slab details for below grade basements.

Shown above: Insulation, moisture and drainage control for below grade slabs. Note interior footing vent and weeping tile for radon (if required) - drain to exterior weeping tile. Air barrier not a concerns as concrete slab and wall are 100% effective. Moisture barrier is required either on top of insulation or on top of prepared fill, under the rigid insulation.[1] Place or spray capillary break between foundation wall and footing. Under entire slab, use type 3 or 4 high density rigid insulation. Do not use foil backed bubble insulation. Backfill around weeping tile with washed rock. Backfill excavation with free draining materials. Do not backfill with expansive clays.

1. Military / NASA Unified Facilities Guide Specifications UFGS-07 21 13 (August 2010), item 3.6.3 states, “Install insulation on top of vapor retarder and turn retarder up over the outside edge of insulation to top of slab.” CMHC and BSC both state overtop is the recommended practice.

1. Swinton, M.C., Kesik, T., Performance Guidelines for Basement Envelope Systems and Materials, Final Research Report, Institute for Research in Construction, National Research Council Canada, October 2005
2. Straube, J., Smegal, J., Building America Special Research Project: High-R Walls Case Study Analysis, Research Report – 0903,  March 11, 2009 (rev. 8/7/09)
3. Straube, J., Smegal, J., Building America Special Research Project: High-R Foundations Case Study Analysis, Research Report – 1003, 20 August 2010
4. Hutcheon, N.B., and Handegord, G.O.; Building Science for a Cold Climate, ISBN 0-9694366-0-2, National Research Council of Canada, 1983

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