Insulating a basement makes it warmer, cuts heating bills, and is essential before finishing. But basements are damp and cold against the concrete, so doing it right — with moisture control — is what prevents hidden mould.
Solve moisture first
Before insulating, fix any water issues: grading, gutters, drainage, and cracks. Insulating over a damp wall traps moisture and breeds mould. Confirm the basement stays dry through a wet season.
Choose the right assembly
Common approaches include rigid foam board against the concrete (which controls moisture and condensation), or a framed stud wall with insulation kept slightly off the cold concrete. The key is preventing warm, moist indoor air from condensing on the cold wall — get the vapour control right for your assembly.
Don't trap moisture
Avoid putting fiberglass batts directly against bare concrete or sandwiching insulation between two vapour barriers. When in doubt about an existing basement, consult a building envelope professional — basement assemblies are where moisture mistakes hide.