Foam is less permeable to water vapor and the back of the siding stays wet as the face of the siding dries.
Insulation between osb and siding.
Unless you provide a small gap between the exterior face of the osb and the back surface of the foam sheathing to provide for some hygric redistribution.
Isobrace osb rigid insulation for above grade exterior walls laminated to a 7 16 osb.
Many houses built today have a double wall type of insulation with fiberglass batts fastened between the studs on the inside and rigid foam board over.
Below are some of the design details along with the benefits.
This detail is used with both new construction and also with renovation work.
How to install rigid foam under siding.
Everything on the exterior side of the polyiso the furring strips and siding will dry to the exterior while everything on the interior side of the polyiso the osb studs and fluffy insulation will dry to the interior.
As a result the siding cups cracks and sheds paint.
Isobrace osb combines the insulation performance of an expanded polystyrene panel with the rigidity of a 7 16 oriented strand board osb.
If you prefer to use polyiso without a foil facing feel free to do so.
Yes closed cell high density foam cavity insulation applied to the inside of osb sheathings that are in turn covered on the exterior with impermeable foam sheathings is risky.