Walls and slabs
Similarities of building enclosures for
cold climates to
cold climate outdoor gear.
Cold climate sports gear serves as a suitable analogy for
sleeping bag represents the insulation,
VB liner as a vapor barrier and fabric such as
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 and characteristics.
NRC-IRC: Building Science for a Cold Climate,
dog eared and coffee stained...my favorite book. Authored by
Hutcheon and Handegord - first published in 1983 it remains
today as an authoritative resource.
Walls and slabs for cold
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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
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
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.
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).
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.
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
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
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
Shown above: Insulation,
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. 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