Almost every Quebec home with a basement has one: that small, uninsulated storage room tucked under the front steps. It's also, almost without exception, the first place mold shows up in a basement.
The Design Itself Is the Problem
Cold rooms are built deliberately uninsulated, with concrete walls in direct contact with the ground outside. That also means the walls sit at a temperature well below the dew point of indoor air for a good chunk of the year.
When warmer, moisture-carrying air enters the cold room, it hits those cold concrete surfaces and condenses. Add minimal air circulation, and you've created the exact conditions mold needs.
Why It Keeps Coming Back
Surface cleaning never addresses the moisture problem. Concrete is porous; surface treatment doesn't reach what's absorbed into the material, and does nothing to stop the next condensation cycle.
What Actually Works
A proper cold room treatment has to do three things: remove the existing mold from the porous concrete surface, treat the material to prevent regrowth, and identify whether better sealing, drainage, or ventilation is needed.
In some cases, the fix is straightforward. In others, particularly older homes with no vapor barrier, the underlying moisture issue is more persistent.
A Quick Note on Stored Items
If you're storing anything porous in a moldy cold room, assume it's contaminated too. Treating the walls while leaving contaminated shelving in place is a common reason mold seems to "come back" immediately.