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Rigid foam installation question

Y_Knot | Posted in General Questions on

We are renovating a single story house with 2×4 walls and adding 1.5” foam to the exterior. We are doing “innie” windows. Unfortunately,  contractor has already installed the new windows. To ensure durability, I’m thinking of a picture frame around the windows of 2×4’s (on top of Tyvek) and having the foam butt up to it. Then taping 2×4’s to foam and then flashing from windows out to edge of 2×4’s. Tops of windows are well protected by 24” overhang but would flash top of the picture frame as well. I’m also planning to put 2×4’s on the corners of the house and have foam abut.

Im planning on treated lumber for those 2×4’s. Should I do the same for my furring strips? Seems like consensus is that it’s not necessary.

– Drip edge at bottom of foam
– Glue edges of foam 
– 4.5” headlok screws to fasten foam/strips
– tape seams
– SV5 Coravent at bottom
– coravent at top or vent into soffit???
– treated 2×4’s around windows and on corners (plus furring strips)

Does that all sound okay?

Thank you!

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  1. jaywbee | | #1

    Using nominal lumber around openings is a common practice when using exterior continuous insulation. Do a search on "buck boards." Check out this video series on how to flash a window using buck boards -

    That said, depending on what your siding material is, there's a good chance that you DO NOT want to use treated lumber (review install guides). Chemicals from treated lumber can and will leech into your siding product if not furred out with a rain screen or similar.

    1. Y_Knot | | #2

      Oh wow, thank you! The buck board and leaching info are both super helpful!

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