A.Paul Fisette, director of Building Materials and Wood Technology at the University of Massachusetts Amherst and a JLC contributing editor, responds: According to the National Oceanic and Atmospheric Administration (NOAA), your house is in a climate that averages 4,700 heating degree days, 1,000 cooling degree days, 44 inches of rainfall, and 34 inches of snow annually. And according to the 2009 International Energy Conservation Code (IECC), you’re in climate zone 4. Therefore, your goal should be to insulate the walls with at least R-13 wall insulation. It’s reasonable to assume that water penetrates the brick weather barrier at least occasionally, but because the wall hasn’t been insulated in the past, the wall cavity has been able to dry to the indoors with little permanent damage. However, the new insulated wall system should resist water intrusion altogether, so filling the cavity with blown cellulose alone wouldn’t be adequate.

The existing balloon framing will make it difficult to install an exterior housewrap to protect the cavity wall. Instead, strip the interior wall surface covering so that you can spray closed-cell urethane foam directly onto the back of the brick. To keep the bricks from absorbing rainwater, first install polystyrene cathedral roof vent chutes...

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