Any suggestions for building a well insulated flat roof, u-value < 0.08 like the pitched roof?
Filling the pitched roof loft with 500mm of mineral wool does the trick there, but it seems difficult to get anywhere near with a flat roof. Wanted to just stuff mineral wool into a flat roof truss, but that would be a cold deck and suffer condensation problems if incorrectly vented. Everywhere says cold decks are no longer recommended, but there is a practical fixing limit to how much rigid insulation board can be attached above the rafters. Warm decks I have seem just aren't that insulated.
German passive houses seem to have lots of flat roof, so how do they do it? Anyone?
Filling the pitched roof loft with 500mm of mineral wool does the trick there, but it seems difficult to get anywhere near with a flat roof. Wanted to just stuff mineral wool into a flat roof truss, but that would be a cold deck and suffer condensation problems if incorrectly vented. Everywhere says cold decks are no longer recommended, but there is a practical fixing limit to how much rigid insulation board can be attached above the rafters. Warm decks I have seem just aren't that insulated.
German passive houses seem to have lots of flat roof, so how do they do it? Anyone?