Crawl spaces are among the most neglected areas of Ontario homes — and one of the highest-return areas to address for energy efficiency and moisture control.
The Problem with Vented Crawl Spaces
Traditional vented crawl spaces allow humid summer air under the home. Warm humid air meets cooler crawl space surfaces, condensation forms on wood framing and insulation — creating mould, rot, and pest habitat. Building science has largely concluded: sealed, conditioned crawl spaces outperform vented crawl spaces in Ontario climates.
Full Encapsulation (Recommended)
Seal the crawl space completely: 20-mil vapour barrier on floor and all walls. Seal all foundation vents. Insulate perimeter walls (closed-cell spray foam or rigid foam). Connect to HVAC or add a dehumidifier. Cost: $5,000-$15,000 for a typical Ontario crawl space.
Floor Insulation (If Not Encapsulating)
Insulate floor above using batts between joists — minimum R-20. 6-mil vapour barrier on soil. Batts must be held firmly against subfloor. Sagging batts lose effectiveness and create pest harborage.
Address Moisture Sources First
Standing water or active seepage must be fixed before any insulation or encapsulation work. Grade away from foundation. Verify weeping tile function. Insulating over a wet crawl space creates a mould factory.
Discuss crawl space encapsulation and find Ontario insulation contractors at home.renovation.reviews.
The sealed vs vented debate is mostly settled on the building science side, but I still see vented crawl spaces spec’d by contractors who haven’t updated their approach since the 90s. A few things worth adding from the field.
The 20-mil vapour barrier spec here is the right call. On older Ontario homes we often find 6-mil poly that has been down for 20 years - seams opening, moisture still migrating through. When you’re getting quotes, ask the contractor specifically what mil they’re using and how they’re handling overlaps and penetrations (pipes, columns). That’s where the cheap jobs fail.
One cost note: the $5,000-$15,000 range is reasonable for a straightforward rectangular crawl, but older Ontario homes often have uneven perimeter walls, partial concrete footings, and low clearance that push labour well above that. If a contractor quotes the low end sight-unseen, get a second opinion.
A few things that get skipped but matter: the perimeter wall insulation connection to the rim joist needs to be continuous - a gap at the top where the floor framing begins can bleed most of your thermal benefit. And if you’re adding a dehumidifier rather than connecting to the HVAC, make sure it has a condensate pump and drain line. A unit that overflows its collection bucket defeats the whole purpose.
Worth getting quotes from companies that handle both waterproofing and encapsulation together - the two systems need to be designed as one, not bolted on separately.