# Cold flat roof - no space for ventilation...?



## Windows on Wash (Aug 30, 2011)

Is the roof being re-done?

You could strap the roof and create a new vent space above but if not, the easiest thing is probably SPF in this case.


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## Gary in WA (Mar 11, 2009)

Welcome to the forum!

Another option is R-15 rigid foam board (XPS or EPS w. vapor barrier) insulation tight to roof decking and canned foam the joints/perimeter. That would give you 43% Relative Humidity in the house before condensation (board sheathing at 44*F), same as Zone 4a (see map) here; http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Gary


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