A crawl space in a cold climate requires moisture control. Which option describes the most appropriate vapour barrier strategy for the ground beneath the crawl space?

Question: A crawl space in a cold climate requires moisture control. Which option describes the most appropriate vapour barrier strategy for the ground beneath the crawl space?

Answer options:

• No vapour barrier is needed; natural ventilation will handle moisture.
• A woven geotextile fabric directly on the soil, covered with gravel. ✅ A 6-mil (0.15 mm) polyethylene sheet, overlapping seams by 300 mm and taped, extending up foundation walls.
• A thin, breathable membrane that allows soil moisture to escape upwards.

Correct answer: A 6-mil (0.15 mm) polyethylene sheet, overlapping seams by 300 mm and taped, extending up foundation walls.

Explanation: A 6-mil polyethylene sheet with properly overlapped and taped seams, extending up the foundation walls, provides an effective vapour barrier over the soil in a crawl space. This prevents ground moisture from evaporating into the crawl space air, reducing humidity and potential condensation issues in the structure above, as per NBC 2020 guidelines for ground covers.