I have a project in the Boston area where I would like to add and inch or so of rigid insulation to add some R value and knock down the thermal transfer and air-seal. The problem I'm saddled with is the wall that I need to work on is the gable end of the house and I'd have to extend the roof and move the electric meters and weather head if I thicken up the exterior wall by adding the foam and rain screen, and also add the new siding.
Some of the wall has the original fiberglass in it, and some we're going to put open cell into ( repairing leaky wall and I will take down wall board and replace old fiberglass) . I am wondering if I put the rigid on the inside of the condition space ( preferably going over the wallboard where the fiberglass still is,) will I end up with condensation on the exterior side of the rigid or inside the wall cavity. I defiantly want the follow the "do no harm" rule.