my father in law is replacing his roof in malibu, CA. He has asked for advice from me regarding whether a vapor barrier is required on the underside of the rigid insulation in a torch down roof assembly. In Fairbanks we would always have a vapor barrier on the warm side of the insulation. Does he need a vapor barrier in this location? It potentially would be located between an existing 2X6 t&g roof and 2" of polyiso rigid insulation. ON top of this would be a protection board, 75# underlay and topped by a torch down granular roof.
Thanks
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David Hayden AIA
L64 Design, Ltd.
Fairbanks AK
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