Crawl Space Encapsulation, Lower Sackville

The smell was the symptom

The homeowners had been chasing an odour on their main floor for two years. They had cleaned ducts, replaced carpet, and run a dehumidifier upstairs continuously. None of it worked, because the source was below the floor.

The stack effect explains why. Warm air escapes through a house’s upper floors, and replacement air is drawn in at the lowest point. In this house that was a vented, dirt-floored crawl space. A large share of the air circulating on the main floor had passed through it first, carrying moisture, odour, and mould spores up with it.

What was found

The crawl space had six open foundation vents: standard practice when the house was built, and exactly backwards for our climate.

In summer, outside air at 22°C and high humidity enters those vents and meets crawl space surfaces sitting at 12 to 14°C. The air cools below its dew point and the moisture condenses onto the joists, the ductwork, and the insulation. The vents were not drying the space; they were delivering water to it every warm day.

The result was predictable: fibreglass batts hanging down black and saturated, white surface mould across the underside of the subfloor, and thin builder’s poly that had torn and slid so that most of the ground was open dirt.

What was done

Everything came out: debris, failed barrier, and all the saturated insulation, which had no remaining insulating value and was acting as a mould substrate. Surface growth was remediated before anything was sealed.

The ground and walls were covered with a heavy reinforced vapour barrier, lapped up the walls, mechanically fastened near the top, and taped at every seam so the whole space behaves as one continuous membrane.

The vents were sealed. The rim joist, a major source of both air leakage and condensation, was sealed and insulated. Every plumbing and wiring penetration was sealed.

A small dedicated dehumidifier with a routed condensate line handles the remaining drying load, and now runs very little.

Result

The odour was gone within a week. The floors above the crawl space are no longer cold underfoot, and indoor humidity is controllable for the first time.