Air Gap for Foil Vapor Barrier
Purveyors of foil radiant vapor barriers (https://atticfoil.com/index.php/about-radiant-barrier/why-is-an-air-space-required/) say that an air gap is needed for this to work. True?
When used in the wall of a sauna for instance (I think primarily because foil can withstand heat that other vapor barriers cannot) they suggest installing the foil to the studs then 1/2″ furring strips and then the interior wood (typically T&G cedar or similar). The walls are typically insulated (batts, blown or sprayed) to the outside of the foil but the inside is facing a sauna that could be 200°f or more so like Martin’s steel roof example (https://www.greenbuildingadvisor.com/article/radiant-barriers-a-solution-in-search-of-a-problem), perhaps does offer some energy benefit?
So a typical wall might be exterior cladding + sheathing + studs & batt insulation + foil radiant vapor barrier + furring strips + T&G hemlock.
Is some way of venting this space needed? Both supply and exhaust venting? Or will radiant heat simply be reflected back to the interior sauna walls?
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