# Insulating unvented flat roof



## Windows on Wash (Aug 30, 2011)

The industry standard in this case would be to use closed cell phone. That being said, I've seen open cell phone used successfully as long as you control the moisture from the interior side and have an airtight drywall ceiling. 

What is the joist size currently?

Spray foam is going to be your easiest and most comprehensive approach that usually cannot be fouled up.

You can always ventilate the roof should you decide to go a different route.


----------



## charliefreak100 (Jun 20, 2014)

Thanks for the reply. Yep, I think we're going with sprayfoam. The joists are 2 foot centers. I don't think we'll get a really airtight ceiling - would it be safer to use closed cell rather than open?


----------



## Windows on Wash (Aug 30, 2011)

For roofs, closed cell is more safe but make sure you use a good SPF company. This can't be put on incorrectly or it can burn down the home.


----------



## federer (Aug 20, 2010)

Windows on Wash said:


> For roofs, closed cell is more safe but make sure you use a good SPF company. This can't be put on incorrectly or it can burn down the home.


 how would it burn down the house?


----------



## Windows on Wash (Aug 30, 2011)

federer said:


> how would it burn down the house?


http://www.businessinsider.com/5-million-connecticut-mansion-fire-2014-7

Closed cell foam curing is a high exothermic reaction. 

If you apply the foam at too much thickness, the foam will actually serve to insulate the heat that should be coming out of the foam during the curing process. 

The additional trapped heat in the foam can get so high that the foam will combust. 

Scary stuff if not done right.

By the way...the owner of that home in the article is the owner of a huge company that does, amongst other things, spray foam. Just goes to show that you really need a good company doing the installation.


----------

