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Community and Q&A

Horizontal steel siding on house

user-2069108 | Posted in Green Building Techniques on

We are going to be applying 6″ of polyiso foam to the outside of our house. It will likely be 3 layers of 2″ material. I have concerns related to the potential waviness of the siding plane. The steel siding, applied horizontally, seems to be very unforgiving. Has anyone tried this? And with what success?

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  1. GBA Editor
    Martin Holladay | | #1

    What brand of siding will you be installing?

    Polyiso is fairly firm -- much firmer, for example, than mineral wool. If you want to be sure that the crew installing the furring strips pays attention to making sure that the furring strips are co-planar, let them know about your concern.

    It should be a simple matter to check if the furring strips are co-planar with a long straightedge or a high-quality 2x4. Adjustments can easily be made by torquing down a few screws or using shims.

  2. Expert Member
    Dana Dorsett | | #2

    Jesse Thompson has even used reclaimed foam in exterior layers that thick (it sometimes takes a bit of shimming with used foam), but SFAIK not with steel siding. eg:

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