XPS foam on exterior side of window and door headers
I think have seen a similar question before but wanted to refresh.
Assume building a 2×6 wall. Using Mineral Wool for insulation (which means a smart membrane on the interior side of the wall). When framing headers for doors and windows almost ALL of them only need double 2×8, typically with ply sandwiched to make them flush with the stud depth. In 2×6, simply 3 pieces of header lumber are nailed together to get the 5.5″ thickness of the stud.
Would it be a good idea to actually install 1.5″ of XPS (or EPS) Foam instead of the 3rd additional piece of wood to help with thermal bridging of the header lumber? Would placing it on the interior side warrant any benefit over the outside?
I can’t come up with a reason not to do this. The third 2×8 typically installed in a header is just there for filler and something to nail into, considering most headers only need to be doubled up.
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