Flat roof assembly in a hot humid climate
We are going to construct a very modern home with low pitched roofs (1/4″ per foot on 5 separate roof levels) being constructed of 18″ trusses, utilizing Advantech sheathing for the deck, then a vapor permeable fluid or adhered membrane, then rigid Polyiso board varying from a minimum 1″ thick to 6″ to create the slopes, then Densdeck Duraguard and finally a fully adhered, highly reflective PVC membrane. Underneath the deck, we intend to use 6-8″ of open cell spray foam.
This will leave an air gap of 10-12″ between the top of the dry wall on the ceiling and the bottom of the spray foam insulation below the deck. Will this avoid/decrease the likelihood of condensation issues? Would you advise filling the 10-12″ air gap with insulation or is that over-kill?
We haven’t been able to access some of your prior articles due to website issues (have notified customer service) and have seen some examples from Joseph Lstiburek that show this gap open and some that show it filled depending on the website, and without regards to what climate zone.
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