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Covering for 2-inch rigid foam at base of siding?

hallie17 | Posted in Energy Efficiency and Durability on

I am considering a 2×6 wall assembly covered with plywood sheathing plus 2 inches of rigid foam under fiber-cement siding with a rainscreen. This will probably go over an ICF foundation.

I am not finding a detail for this specific situation, but similar details on GBA suggest having the sill plate align with the ICF. This will mean that there will be 2″ of foam exposed at the bottom, projecting past the foundation.

Is it necessary to have a piece of aluminum or similar protection covering the foam? Could you just cover it with weather resisitive barrier? Or simply let the siding project down past it by 3/4″ or so?

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  1. GBA Editor
    Martin Holladay | | #1

    Yes, the bottom edge of the rigid foam should be protected with metal flashing. Here is a GBA video that shows you exactly what you need to know: Video: How to Install Rigid Foam Insulation Outside a House.

  2. hallie17 | | #2

    Thanks for the video! It took a while to put together all the pieces presented there, especially since you can't still frame the video without it going dark, but I think I've got it. I don't think the detail library has all of this laid out clearly in any one detail right now, with everything from the drip edge to wrapping both the foam and the bottom of the furring strips with insect screen. But I did know for certain I could get the info I needed here!

  3. GBA Editor
    Martin Holladay | | #3

    In case you haven't seen it, there is more information here: How to Install Rigid Foam Sheathing.

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