Insulate the Inside Walls of a Solid Masonry Brick House []

Question:

Can I build an insulated interior wall inside my plaster walls on my brick house for better insulation? I want to apply Styrofoam to the inside plaster surface of my brick house, on each exterior wall inside each room to better insulate that wall. Will that work to insulate these exterior walls?

Answer:

Yes it will. It will also diminish the size of the room the thickness of each wall you build.

You will need to fir out the jamb thickness of each door, window, and base board that gets re-installed. As the wall gets thicker then so will the jamb thickness of each penetrating window and door frame.

You must make certain that the exterior brick is fully tuckpointed and effectively sealed from the outside to prevent any water penetration through or into your wall cavity. This is very important. make the exterior wall surface water proof.

I suggest you then seal the inside plaster wall with a solvent or oil based paint to better resist any possible moisture penetration through the outside brick.

Then apply firring strips 16″ on center, equal to the thickness of the rigid foam insulation you have selected. I suggest 2″ thick rigid Dow Styrofoam, blue color, which is suitable for moist or below grade applications. This below grade application label means it is not adversely affected by moisture. Use a 2″ thick firring strip, applied 16″ on centers with masonry anchors to the brick wall. This will take some time, effort and expense. cut your Dow board to fit between the firring strips. Then install the Dow rigid blue board to the plaster wall surface with an appropriate glue between the firring strips like an insulation between the wood studs on a frame wall. Install 1/2″ or 5/8″ thick regular drywall, (not moisture board or green board drywall) to the firring studs.

Tape & finish the drywall in traditional fashion. Then paint the wall with a latex primer and a latex top paint coat. Do not use an oil or solvent base paint. Latex paint allows moisture migration to escape from inside your new wall cavity if it should ever enter. Then complete your jamb extensions and trim application of the base and casing trims around the windows, doors and floor.