Henry has completed a basement renovation at his 1950s Toronto bungalow and is now grappling with an unexpected problem: One room of the house smells strongly of old, damp brick.

From all appearances, the renovation was done carefully. The foundation wall, consisting of concrete block with brick above, now includes exterior waterproofing, damp-proofing membranes, and a layer of closed-cell spray polyurethane foam in an interior 2×4 wall.

And yet, he writes in a Q&A post, all is not well.

The odor is coming from the floor and/or wall of one of the rooms in the northeast part of the house, which is located directly over the basement laundry room.

“I am not getting the smell anywhere else on the first floor,” Henry writes. “It seems to be strongest when the temperature changes drastically between inside and outside, i.e. the weather has been cooler the last few days and it’s less noticeable, although I haven’t correlated a specific trigger for the smell.”

There’s no smell in the laundry room itself, and he’s found no evidence of either a leaky dryer vent or water leak. Nor has an extensive check of the attic and basement walls uncovered any visible water. Henry is beginning to suspect the cause is an uninsulated air gap at the perimeter of the floor framing, as suggested by the drawing at the top of this column. He’s thinking of adding more spray foam to close the gap.

Is he right? And if so, what should he do about it? That’s where we start this Q&A Spotlight.

Insulate and add a capillary break

Zephyr7 suspects the odor is indeed coming from the damp block via the gap shown in the drawing. Because the block is sealed on the…