Crawl Space Encapsulation for Airdrie & Rocky View Homes

The Problem It Solves

Crawl spaces tend to be left as built: a bare dirt or gravel floor, maybe a thin sheet of poly that has shifted or torn over the years, fibreglass batts stuffed between the floor joists, and a couple of vents in the foundation wall. That treats the crawl space as outdoors, and it serves neither side well. Cold air comes in through vents and gaps, the floor above stays cold, and ground moisture evaporates into the space all year.

The ground under a house is always damp, even in a dry climate like ours. Moisture rising from exposed soil raises the humidity in the crawl space, and that moisture finds the coldest surfaces: the rim joists, the underside of the subfloor, ducts and water lines. Batts between joists sag and fall once damp or nested in. Musty smells, stained or mouldy framing, frozen pipes in a cold snap and cold floors in the rooms above are the usual complaints that bring someone to open the hatch.

The crawl space is also a pathway for soil gas. Radon is released from the ground across the Calgary region, and Health Canada testing has found elevated levels in a meaningful share of homes in the area. Air in the crawl space moves up into the house through plumbing holes, duct chases and gaps in the subfloor, carrying whatever the ground is giving off, and a bare dirt floor offers no resistance to it at all.

How It Works

Encapsulation moves the building's thermal and moisture boundary from the floor above down to the crawl space perimeter and ground. First, the ground is covered with a reinforced polyethylene liner, commonly 10 to 20 mil, much tougher than builder poly so it survives being crawled over for years. Seams are lapped and taped, piers are sealed, and the liner runs up the walls where it is fastened and sealed. That closes off the soil moisture and makes it far harder for soil gas to move freely into the space.

Next, the perimeter walls and rim joists are insulated with 2 lb closed-cell spray foam. Closed-cell foam bonds to concrete and wood, resists water, air-seals and, at sufficient thickness, controls vapour, all in one layer. Insulating the walls instead of the floor keeps pipes, ducts and the subfloor inside the warm zone. Exposed foam in the crawl space is then protected as its listing and the inspector require, often with an accepted intumescent coating where drywall is impractical.

Finally, the space has to be managed as conditioned space. Crawl vents are closed only when the design provides for it, typically a small supply of conditioned air from the furnace or a dehumidifier sized for the space. Where radon is a concern, the membrane is sealed carefully and a sub-membrane depressurization option is kept or added so a fan can be fitted later if long-term testing shows it is needed.

What Decides the Specification

The liner thickness is chosen for how the crawl space will be used. A crawl space that houses the furnace or plumbing access gets crawled through regularly, so a heavier reinforced liner is worth it; a space that is rarely entered can use a lighter one. The wall foam thickness depends on the insulation value being targeted, the foam's vapour-control properties at that thickness, and the height of wall exposed above the ground.

Conditioning is the design decision people most often skip. A crawl space served by a forced-air furnace can usually take a small supply register. One without ductwork may be better with a dehumidifier and drain. Seasonal seepage means drainage or grading is fixed before encapsulation, not after. Radon plans change the membrane detailing, including whether a perforated pipe is laid under it. Where the house is a mobile or manufactured home, the manufacturer's rules for the skirting, frame and belly govern what can be sprayed.

Around Airdrie

Full crawl spaces are less common in Airdrie's newer subdivisions, where full basements are the norm, so most of the crawl spaces we see are elsewhere. Older homes in Crossfield and Irricana sometimes sit partly or wholly on crawl spaces, and additions and sunrooms built onto basement houses often have a shallow crawl under them that was never insulated properly. Acreage homes across Rocky View County, including many manufactured homes on skirting, are the other main source. On open prairie, wind drives cold air through crawl vents and skirting gaps, which is why frozen lines and cold floors are common winter calls there.