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Insulating a Flat Roof

DarylFitz | Posted in General Questions on

I know this has been discussed at length… I have a new construction house in zone 5 with a small (80 sq ft) flat roof.  I have read and researched how to insulate this and seem to get confused and forget while trying to bring all the info together into a plan. This is what I think I need to do along with a few questions.

EPDM roof membrane
??osb or poly iso with fiberglass??  When the EPDM needs changed will the osb be easier?
at least r20 of ??expanded or extruded polystyrene?? expanded is certainly cheaper and I have plenty of space.
osb
fiberglass batt to give a total of R49 touching the osb ??can this be faced??
air space
drywall ceiling
I know not to use polyethylene but do I need an air barrier other than the drywall?
 
Does the foam and roof decking need to be mechanically fastened or can I use adhesive between layers?
 
Do both layers of OSB need taped?
 
Thanks
Daryl

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