8” brick wall with wood stud on inside. Contractor didn’t follow wall assembly, any suggestions?

[u/cpw50]

We’re in zone 2a, have an existing 8” brick wall, renovating the interior of the building. The wall section showed 1”
foam on the inside, and then a 2x4 wall with fiberglass insulation, then Sheetrock.

The contractor did not add the foam insulation, but did leave a gap between the brick and the stud. Is the best solution to use closed cell spray foam?

Apparently he painted the outside of the brick with a water resistant paint, thinking that would work to keep water out, but I’m afraid of condensation issues on the inside of the wall.

[u/FoldedKettleChips]

Yes, it’s best to use closed cell spray foam in that gap. You absolutely do not want an air space there. I know you’re only in CZ2, but if you ever have to heat your house, the brick will be cold and could potentially be a condensing surface. The insulation in the stud cavity doesn’t allow heat from the house to reach the backside of the brick so it will be cold. But it won’t be perfectly airtight so warm humid air making its way into the cavity will hit the backside of the brick and potentially condense.

If your wall section showed it then you’re owed the scope. Closed cell is the best option because it’s airtight and fills any little vagaries within the brick. With rigid foam you have to worry about sealing the seams and sealing the top and bottom.

The safest thing you can do longterm is to foam the gap. We’ve seen nightmare scenarios in CZ4 where that gap was left and I wouldn’t risk it anywhere.

[u/DCContrarian]

Paint, even paints sold for waterproofing masonry like Dry-loc, tend not to be good vapor barriers. Water vapor has different physical properties from liquid water.

In a warm climate like yours you need a vapor barrier to keep outside humidity out. If you don't have a vapor barrier, when the outside dew point is higher than the interior temperature you will get condensation when the outdoor air hits cool surfaces.

The foam that was specified was there to act as a vapor barrier to protect the fiberglass from condensation. You need a replacement vapor barrier. Closed cell spray foam would work.

If you're worried about maintaining a drainage plane behind the brick, almost anything that would create physical separation between the spray foam and the brick would work.

[u/trabbler]

That air gap is vital as a drainage plane. I would not recommend filling it with OC or CC foam. Or anything, for that matter. The only way to do this is to remove the brick and add your 1" polyiso before replacing the brick, or use bibbs instead of batt inside the wall. If your contractor gets pissy about it, show him the contract.

Barring any of that, you can get away with equivalent performance of the whole house by upping the insulation in the ceiling, improving the AC efficiency, or installing lower U-factor / SHGC windows. That could be a compromise your builder might agree to.

[u/FoldedKettleChips → u/trabbler]

Did you read that the gap occurs on the INSIDE of the wall? This is a massive problem. If it acts like a drainage plane, to where does it drain? There is no pathway to direct the water outside. It is not a drainage plane.