Crawl Space Insulation

A crawl space is an unfinished, accessible area below the first floor of a building. The main purpose of insulation is to enclose the living space in a thermal envelope — so if the space below a floor is unconditioned, either the floor or the walls below it must be insulated.

There are two types of crawl spaces: vented and unvented. Vented crawl spaces open to the outside, while unvented crawl spaces are part of the basement. How and what is insulated depends on which type you have.

In a vented crawl space, the underfloor should be insulated — much as it is in ceilings — before or after the sub-floor is applied. In an unvented crawl space, you should insulate the perimeter walls.

Seal the Walls, Not the Floor Above

The old approach was to insulate between the floor joists and leave the crawl space vented to outside. In our climate that tends to fail: the batts sag, the space stays cold and damp, and pipes and ductwork run through an unconditioned zone. The better method for most Ottawa homes is to seal and insulate the crawl space walls, bringing the space inside the building envelope.

• Closed-cell foam on the perimeter walls and rim joist
• Warmer floors in the rooms above
• Pipes and ducts kept within the conditioned space
• Reduced humidity, mould and musty odours
• Discourages insects and rodents by closing entry paths

Moisture, Odour and Air Quality

Air in a crawl space does not stay there. Stack effect draws it up into the living space, bringing humidity, mould spores and soil gases with it. Sealing the crawl space is as much an indoor air quality measure as an energy one, and it is usually the fix for a house that smells musty no matter how much you clean.

Tight Access Is Not a Problem

Crawl spaces are awkward, low and often partly obstructed. Spray foam suits them precisely because it is applied through a hose and expands to fill irregular spaces, rather than needing full-size rigid boards or batts manoeuvred into position.