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Best exterior veneer for very thick exterior foam sheathing

W. Timothy Ward | Posted in Green Building Techniques on

My wall plans for a new addition now call for 2×4 framing, OSB sheathing, rubberized adhesive membrane and 7 inches of Atlas R board poly iso insulation with 1×4 vertical furring. My original intent was to use metal siding by Firestone. A recent Building Science white paper on cladding attachment through exterior foam raised some potential long term issues with “heavy” siding over 6 inches of foam. My architect is currently recommending the use of light weight aluminum soffit sheathing as the siding. Has anyone done this before? Any better recommendations for a different light weight siding other than vinyl which I don’t like for aesthetic reasons ? I also am not too keen on wood because of the maintenance issues.

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  1. GBA Editor
    Martin Holladay | | #1

    One possible solution is to scale back from 7 inches of polyiso to 6 inches of EPS, for two reasons:

    1. Recent modeling studies raise questions about the cold-weather performance of polyiso (see In Cold Climates, R-5 Foam Beats R-6).

    2. Plenty of builders have successfully installed heavy siding on 6 inches of rigid foam.

    For more information that supports the idea that heavy siding can be attached to furring strips screwed through 6 inches of rigid foam, see:

    REMOTE: A Manual.

    Fastening Furring Strips to a Foam-Sheathed Wall.

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