Improving attic insulation
We are looking to finish our walk up attic space. It was roughed in with electrical and the 12 inch rafters were insulated with fiberglass batt insulation and ventilation baffles when the house was built. I had an energy audit and the guy said it was one of the best jobs he had seen using batts and that it was insulated very well considering. I would like to improve it and remove thermal bridging, so I was planning on putting a layer of rigid foam on the underside of the rafters and dormers to create a thermal break and improve the air tightness of the room. My question is do I need a specific thickness to accomplish this? Thicker would provide more R-value, but would a 1 inch or less create the desired results of a thermal break and air barrier that I am looking for? I would like to keep costs down, but not at the expense of doing it properly. Thanks.
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