Okay, I’ll admit it. What we’re doing with the exterior walls may seem a little odd. Since the house is structural masonry there is no easy way to insulate the exterior walls, let alone add electrical outlets or light switches. We’ve opted to fur out the walls on the interior to provide space for insulation and utilities.
Framing these walls, however, posed an interesting problem. On the one hand we want to keep the new framing separate from the brick wall to prevent moisture wicking into the wood. We also want to use the smallest dimension lumber possible maximize the space for insulation in the walls and to stay within budget. We’re insulating the walls with spray polyurethane foam insulation (SPF), which is great at filling in small cracks and works well when the substrate is uneven (in this case a combination of plaster and exposed brick). It also provides some added strength to the wall by “gluing” the components together. SPF is a combination of two liquids that when combined rapidly expand, similar to shaving cream. Unlike shaving cream, it’s rather forceful and can actually bend, twist, and bow wood. So how do you install 2x3s approximately 1 inch off from a brick wall that will be insulated with spray foam?