Plaster on Brick - Remove plaster or keep and frame with drywall

[Alex Ballas]

Should I remove the plaster that is attached to the inside of an exterior brick wall, or keep it and just build a 2x4 frame and insulate, drywall, move outlets.  This is a 4unit low income property that I am upgrading to get better tenants, the plaster is applied directly to the brick and is very cold in winter

[Roy N.]

If you have an external masonry wall, which is exposed to the conditioned space of the unit, then you have very negligible insulation and a massive thermal conduit between conditioned and unconditioned spaces.

You would be doing far better by your future tenants to insulate this wall than worry about loosing 2-3" of living space or the aesthetics of a brick wall.

Where this is a masonry wall - first confirm if it is a single wythe or 2 (or possible 3) wythes of brick (with a air gap/drainage plane between the outer wythe and the inner).   If you have multiple wythe of brick, you should be able to either affix 2- 4" (in layers of 1", 1.5"  or 2") of foil faced polyisocyanurate rigid insulation (tape all seams and stagger the seams of each layer), or spray the inner surface with 2 - 4" of closed cell spray foam insulation.  You can then strap furring strips over the insulation (attached through the insulation into the masonry) and hang drywall or resilient channel and then drywall from the furring.

Polyisocyanurate foil faced rigid foam runs ~R6/inch, while closed cell spray foam runs R6 to R6.4 and provides a better air barrier.

Alternatively, you could stand-up a 2x3 or 2x4 studwall in-front of the masonry wall (leave a 1/2" gap between the masonry wall and the studs and spray the stud cavities (and space behind the studs) with closed cell spray foam.   Though it's really unnecessary to build a stud wall.

If your masonry wall is only a single wythe of brick, then applying closed cell spray foam to the back of the wall could prevent it from drying properly, eventually leading to spalling of the outer brick surface as it absorbs water (there are ways to mitigate this, but you will want to bring in someone with experience).