The Pretty Good House Blog: Renovating Existing Walls

If you're renovating rather than building new, opening up your walls is a chance to fix problems and improve comfort, but the options are usually narrower than they'd be for new construction. Architectural goals often come first, so the real question becomes how far it makes sense to go once the walls are already open.

Before touching insulation or air sealing, the framing itself needs a look. Renovation work often uncovers rot, insect damage, or old framing decisions that need to be dealt with first. There's little point improving insulation around wood that's already breaking down.

Once the structure checks out, the walls need to be understood in terms of how they handle four things, in order of importance: keeping out water, controlling air leaks, managing moisture vapor, and providing thermal insulation. In an existing house, these jobs are often split across materials that weren't designed for them. Siding and roof overhangs may be doing most of the water-blocking work, old plaster may be limiting air movement, and paint may be controlling some vapor, while the actual insulation may be doing double duty as a filter against drafts rather than working as intended. Recognizing which materials are already handling which job is the starting point for deciding what's worth upgrading during a renovation, and what can reasonably be left alone.