Reducing thermal bridging without creating moisture issues
I am currently working on an estimate for an exterior remodel of a high end home in Northwestern NJ (E5 zone…I believe?) and need some advice. I have been a remodeler for 30+ years, and have tried to keep up with current technologies, but as you know, insulation techniques are ever evolving and difficult to get a straight answer on. The homeowner is somewhat knowledgeable in regards to building practices and wants to try to “tighten-up” his home. The project involves replacing all windows and doors with upgraded units, strip the exterior of the walls to the studs (currently the house only has 3/4″ blue foam as sheathing, except for the corners, which is 3/4″ plyscore. In addition, the foam is riddled with holes from mice…), install new foam to prevent thermal bridging, new sheathing, then Hardee plank siding (or similar). The home was built in the early 1980’s and has 2×4 wall construction with, I assume, R-11 or R-13 fiberglass insulation (paper faced).
After spending hours searching the web for some information, I have become thoroughly confused as to what to advise the homeowner to do. Most techniques discussed are for new structures or complete gut remodels and don’t take into account pre-existing conditions that we are forced to deal with, while trying to upgrade without creating new problems and dealing with budgetary constraints.
If I am understanding things correctly, I could create more moisture issues within the wall cavity by not having enough R value in the foam. As the existing F/G insulation is staying and there is no poly vapor barrier on the interior side of wall, what thickness foam should be used and should I install plywood sheathing over studs first, then the foam? Or foam then sheathing? My other concern is the weight of the cementious siding. If it is only attached through foam to sheathing with ringshank nails, the weight can loosen or bend them over time and create a mess of a callback. I really don’t want to add more layers of strapping due to making the wall thickness so deep that window and door attachment becomes problematic. I have read many answers in your forum, with many idea’s that seem to contradict each other. Also, let’s try using some common terminology for those of us that are not engineers and are trying to educate ourselves and our clients.
Thanks for the help!
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