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Window & door header insulation options – Zone 5

JAC3232 | Posted in GBA Pro Help on

2×6 stud walls, and the header’s have an inside and outside vertical 2×8, with the 2.5” center is empty. The outside sheathing is 1” polyiso with a foil (no OSB or plywood). I want to fill the headers before the windows are installed this week. Drying is to the inside, so no inside VB, and permeability is important. I was thinking 1.5” R6 Roxul ComfortBoard IS or 2” R8 EPS foam. I tried window/door spray foam, but the 2.5” gap was too large, and the foam just falls out to the floor. Am I overthinking this, and I can just stuff it with pink fiberglass?


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  1. GBA Editor
    Martin Holladay | | #1

    Buy some rigid foam insulation with a total thickness of 2.5 inches (for example, 1.5 inch + 1 inch). The rigid foam will do a better job than fiberglass.

  2. JAC3232 | | #2

    I found some 2.5" R10 EPS foam tonight. They're installing the windows tomorrow, so I was able to cut it and get it installed tonight. It worked perfect, with a nice tight fit.

    Thanks Martin, your advice is always appreciated.

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