Crawl Space Insulation.
Insulating the crawl space walls rather than the floor above brings the space inside the building envelope. In Zone 7A that means effective RSI 3.46 (R-19.7) on the foundation wall, and a set of placement rules that decide where the insulation stops.
- 01Diagnose
- 02Price
- 03Repair
Get a Free Estimate
Name and phone is all we need to call you back. Takes ~20 seconds.
24+ five-star reviews
The decision in a crawl space is not how much insulation. It is whether the crawl space is inside the house or outside it. Half-measures — batts in the floor, vents left open, a torn ground sheet — put the assembly in both categories at once, which is where the moisture problems come from.
Foundation walls, slabs, heated floors and unheated floors each carry a different Zone 7A figure — the below-grade table is set out in full in our code guide alongside the above-ground numbers.
Bringing the Crawl Space Inside.
Closed-cell foam on the walls and rim of a crawl space is mainstream, code-recognised use in Canada, and it is one of the places where foam earns its cost rather than merely competing on price.
- Foundation walls to effective RSI 3.46 (R-19.7) in Zone 7A from Table 9.36.2.8.-A; municipal compliance forms show RSI 2.98 in the with-HRV column, which we treat as secondary rather than primary.
- The above-grade portion of a foundation wall follows the below-grade table, not the above-ground one — Sentence 9.36.2.8.(3).
- Unheated floors on ground above the frost line at effective RSI 1.96 (R-11.1); below the frost line the table permits them uninsulated.
- Where insulation goes on the interior of an unheated floor-on-ground assembly, Sentence 9.36.2.8.(4) requires it to continue beneath or above the slab for at least 1.2 m from the perimeter, with a thermal break at the slab edge meeting at least 50 percent of the required resistance.
- The rim and header band, which in a crawl space is the coldest, most condensation-prone surface in the building and effectively impossible to seal with batts.
- Closed-cell rather than open-cell below grade: CAN/ULC-S705.1 caps water absorption at 4 percent by volume, and light-density open-cell product data states plainly that it is not for contact with bulk water or below-grade use.
- Air sealing at the sill, the service penetrations and the crawl space access — Article 9.25.3.1 names limiting soil gas entry as one of the air barrier's purposes, which is not a small point in a crawl space.
- Thermal barrier decisions taken up front: Article 9.10.17.10 carves out concealed spaces within crawl spaces, so foam in a genuinely concealed crawl space needs no covering, while foam in a crawl space that has become a storage or utility room is a different question.
How a Crawl Space Job Runs.
- 01
Decide inside or outside
Insulating the walls and sealing the vents makes the crawl space a conditioned part of the building. Insulating the floor above leaves it outside. Both are legitimate; doing half of each is not.
- 02
Deal with water first
Foam is not a solution to standing water, a failed weeping tile or a grading problem. Anything that puts liquid water against the wall gets fixed before insulation goes on, because closed-cell foam on a foundation wall is effectively permanent.
- 03
Check substrate condition
Manufacturers require a clean, dry, frost-free substrate at 19 percent moisture content or less, at least 3 to 5 °C above the dew point, with relative humidity under 80 percent. A damp crawl space in shoulder season often needs drying and mechanical ventilation before spraying, not after.
- 04
Seal the rim, then the wall
The rim joist band is where the air actually moves. Wall insulation without a sealed rim is a partial answer that will still deliver cold floors above.
Frequently Asked Questions About Crawl Space Insulation
Should I insulate the crawl space walls or the floor above?
Insulating the walls brings the crawl space inside the thermal envelope, which puts any ductwork or plumbing down there in conditioned space and generally gives warmer floors above. Insulating the floor above leaves the crawl space outside and requires the venting and the ground cover to keep doing their job. The Zone 7A numbers differ accordingly: a floor over unheated space is effective RSI 5.02, a foundation wall is effective RSI 3.46. What causes trouble is doing part of both — sealing some vents, insulating some of the floor — because the space then has neither a reliable drying path nor a reliable thermal boundary.How much insulation does a crawl space foundation wall need in Alberta?
Effective RSI 3.46, about R-19.7, in Climate Zone 7A, from Table 9.36.2.8.-A of NBC(AE) 2023. Where the building has a heat recovery ventilator, the widely published figure from the -B table and from municipal 9.36 compliance checklists is RSI 2.98 — we cite that as secondary, because the -B column was not read from the primary code text in our research. The above-grade part of the same wall follows the below-grade table, per Sentence 9.36.2.8.(3), which is a detail people routinely get backwards.Can open-cell foam be used in a crawl space?
It is the wrong material below grade. CAN/ULC-S705.1 limits closed-cell water absorption to 4 percent by volume, and real products test well under that. Light-density open-cell foam is written to a different standard, CAN/ULC-S712.1, which deliberately keeps it vapour-open — later editions actually set minimum permeance floors — and manufacturer data sheets state it must not be used in contact with bulk water or below grade. Open-cell also cannot be a vapour barrier at any buildable thickness: published values run from 362 ng/(Pa·s·m²) at 89 mm to 1 238 ng/(Pa·s·m²) at 50 mm, against a code limit of 60.Does the foam in a crawl space have to be covered?
Article 9.10.17.10 requires foamed plastics in a wall or ceiling assembly to be protected from adjacent space, but excludes concealed spaces within crawl spaces. A crawl space that is genuinely concealed — accessible for inspection and repair but not a used space — falls inside that carve-out. Where a crawl space has become a storage or mechanical room people spend time in, the exclusion is a much weaker argument, and the options are an interior finish from Subsections 9.29.4 to 9.29.9, sheet metal at least 0.38 mm thick with a 650 °C melting point, or a listed thermal barrier. Worth checking with your insurer before choosing a coating over board: a Nova Scotia insurer refused exactly that substitution in 2018 at a documented cost of about $3,700 to the homeowner.Will insulating the crawl space stop the musty smell?
Only if the moisture source is stopped. Sealing and insulating a crawl space changes its air pressure relationship with the house and usually reduces the volume of damp air moving upward, but foam does not dry a wet crawl space and does not fix bulk water. Where a crawl space smells, the sequence is find the water, fix the water, cover the ground, then insulate. Doing it in the other order buries the problem behind a material that is difficult to remove.