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Insulating a crawl space in Kamloops: radon, moisture and where the foam goes

Kamloops crawl space insulation guide: radon testing first, poly ground cover, vented vs closed crawl spaces, rim joist spray foam, fire covering and rebates.

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Home › Guides › Insulating a crawl space in Kamloops: radon, moisture and where the foam goes

Why crawl spaces in Kamloops matter for radon

A crawl space is the part of a Kamloops house closest to the soil, and soil is where radon comes from. Health Canada describes radon as a radioactive gas from the breakdown of uranium in soil and rock, invisible, odourless and tasteless, and the number one cause of lung cancer in non-smokers. It enters through cracks in foundation floors and walls, construction joints, gaps around service pipes, floor drains and sumps. An earth-floored crawl space offers all of those routes at once.

Canada's guideline is 200 becquerels per cubic metre (Bq/m3). Health Canada's Cross-Canada Survey of Radon Concentrations in Homes (2012) found 6.9 percent of Canadians living above that level, and 7.9 percent of tested BC homes. The Thompson/Cariboo health service delivery area, which includes Kamloops, came in at 6.4 percent, and the neighbouring Okanagan at 17.4 percent. Interior Health says radon is common within its region and no level is risk free. In Aberdeen, Juniper Ridge, Rayleigh or Barriere, the only way to know is to test.

Test first, then plan the insulation

Health Canada recommends a long-term test of at least three months with a detector that has passed C-NRPP performance testing. Interior Health says 91 days minimum, ideally over winter, on the lowest floor where people spend more than four hours a day. Kits are sold online and through the BC Lung Foundation.

Test before the insulation job. The BC Lung Foundation states that energy efficiency upgrades to homes can make radon levels worse. Test before, plan the work with that number in hand, then test again after the crawl space is closed up.

Moisture and vapour: ground cover and vented or closed crawl spaces

NRCan's Keeping the Heat In says there must be a moisture barrier on the crawl space floor. If there is none, add one: at minimum 0.10 mm (4 mil) polyethylene, overlapped, caulked and taped at the seams, fastened to the walls and sealed to any wall barrier. Condensation forming under plastic laid on the floor indicates moisture moving up from the ground and the possibility of radon emissions.

The bigger decision is whether the crawl space stays vented or becomes a closed, heated space. NRCan treats heated crawl spaces like short basements and prefers insulating the walls over the ceiling. If the space will be heated, existing vents should be sealed permanently. If it stays vented, NRCan says vents should be at a ratio of 1 to 500 (vent area to floor area), open in spring, plugged and insulated in winter.

Where spray foam goes and what closed-cell does

In a Kamloops crawl space, foam goes in three places. The first is the joist header, or rim joist, the band of wood on top of the foundation wall. NRCan says polyurethane spray foam installed by a certified contractor offers excellent air sealing and insulation of this space. The second is the foundation wall, from header to floor, when the crawl space is closed and conditioned. The third is the underside of the floor above, when the crawl space stays vented and cold.

Closed-cell foam suits these surfaces because it is an air barrier and, at sufficient thickness, a vapour retarder, and it bonds to concrete and wood without a separate poly sheet. Our open-cell vs closed-cell guide covers the differences. For targets, NRCan's Table 2-1 lists a recommended minimum of RSI 4.2 (R-24) for basement walls and RSI 7.1 (R-40) for floors over unheated spaces in Zone 5.

What foam does not do: radon mitigation and fire protection

Sealing a crawl space is not radon mitigation. Health Canada says sealing major entry routes can help reduce radon levels, but their effectiveness will be limited. The most common reduction method is sub-slab depressurization, a pipe and fan system that pulls soil gas from under the house and vents it outside, which Health Canada says can cut radon by more than 80 percent. Interior Health calls active soil depressurization the best and most permanent method, at $350 to $3,000 depending on the site. Health Canada recommends a C-NRPP certified contractor. That is a separate trade from insulation.

Foam also needs fire protection. NRCan says spray foam in the joist space must be covered with fire-resistant material if it is not covered by the basement ceiling and that basement walls are protected with 12.7 mm (half-inch) gypsum board or equivalent. For a crawl space, NRCan says to ask your building inspector whether fire protective coverings are required.

Rebates and a checklist for Kamloops crawl space quotes

The CleanBC Better Homes and Home Renovation Rebate Program, for invoices dated on or after May 15, 2026, pays $0.09 per square foot multiplied by the R-value added for basement or crawl space walls, with a minimum of R10 added, to a maximum of $1,200. A floor over a crawl space or a basement header pays $0.07 per square foot multiplied by the R-value added, with a minimum of R20 added, to a maximum of $1,000. Only one of the two is allowed. The installer must be a Home Performance Contractor Network member and self-installs are not eligible. Our rebates and financing guide has the rest. Ask for these.

Need it hauled or installed?

Call (778) 765-0272 or request a call back. This website connects Kamloops homeowners and builders with a local, licensed and insured spray foam insulation contractor. Calls and form submissions go directly to that contractor, which quotes and completes the work.

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