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Foam insulation panels on stud walls inside or outside?

rsbarch | Posted in GBA Pro Help on

Most details show foam insulation panels added over plywood sheathing on the outside. This generates all kinds of detail problems with windows, flashing, and siding attachment. Yes they can be done. But can these new details be done right by a contractor who has never done it before,.
Why not use polyiso panels on the interior? Joints can be taped and sealed for air tightnes. Furring screwed thru as on some exterior details holds the drywall. I plan to use 3″ or more.
The house can be built in a standard fashion, Works on retrofits. Technically are there problems? Wiring presents some problems.

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  1. GBA Editor
    Martin Holladay | | #1

    The main problems come at rim joists and intersecting partition walls. Exterior foam does a much better job of handling these areas -- and therefore a much better job of addressing thermal bridging -- than interior foam.

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