Insulated Header Question Rigid Foam
I’m building 2×8 headers for a 4′ span for a 2×6 wall as per IBC. Would it be better to use (2x) 2×8’s (min) with 2.5″ of rigid foam sandwiched between or… (3x) 2×8’s with (2x) 1/2″ pieces of rigid foam between?
Also, if I use (2x) 2×8’s with 2.5″ of rigid foam is it OK to use separate 2″ plus .5″ pieces stacked together since 2.5″ pieces are back-ordered? Someone said that may cause condensation.
Also, if I use (3x) 2×8’s with (1x) 1″ of foam instead of (2x) 1/2″ pieces of foam is it better to have the foam closer to the interior or exterior of the structure?
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You aren't comparing apples to apples. Structurally, you either need (2) 2x8s or (3) 2x8s. If you choose to exceed code requirements for the structure, you give up insulation. A better comparison would be (2) 2x10s to (3) 2x8s; those are more structurally equivalent.
The location of the foam doesn't make a lot of difference. There is no risk of condensation when using multiple layers as long as the layers are adjacent to each other. It can be nice to have solid nailing at the interior, but oversized headers are probably the source of most drywall cracks and pushing the framing toward the exterior would help prevent cracking.