# Retrofitting insulation in flat roof



## msmorales (Jun 26, 2011)

Hi all, first post and hoping for lots of great advice! When the master suite was added to our house, it was constructed with a flat roof. Later some misguided remodeler sprayed popcorn stuff on the (very low - 7') ceiling. Here is what I want to do: remove the dry wall (and existing pink batt insulation) thus getting rid of the popcorn, and then - in order to make the ceiling seem a little less oppressive - paint the rafters white, and install white "bead board" between each rafter. However I am concerned about insulation. What can I use between the roof deck and the new beadboard? Rigid insulation, cut into 16" strips? Is there anything I can use that will provide adequate insulation without filling up the entire 6" deep rafter space? If I fill it all up with insulation, it will defeat the purpose of removing the ceiling and trying for the "exposed rafter" look. Might as well just scrape off the popcorn and live with the low ceiling. Any suggestions? Thanks. BTW we live in San Antonio, where heat is a big issue but we do get some cold weather too.


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## Stanchek (May 1, 2011)

You could use the foam insulation board, but you won't get the insulation factor you need. Living in Texas, I doubt three layers of the foam board would give you the r value needed. Can't remember what the r value of the foam board is, you may want to check. Also, maybe radiant barrier with one layer of foam board, then the bead board. Good luck


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## rodeo (Dec 1, 2007)

youre options are very limited.
fitting rigid board into the rafter bays is a PIA
to do right. It is possible though and I have done it
more than once. Hire a sprayfoamer instead if you want to 
go that route. But do you really want to go that route?
I say skip the whole idea of rigid or even sprayfoam. Not worth it.
Its also a fire hazard to have exposed foam - must be covered by drywall.

The best way to do this is to insulate above the deck with rigid.
This would require the roofing membrane to be removed so its typically only practical when reroofing/ during construction. 
If done this way, you could remove all the insualtion inside and have the exposed rafter look.
If reroofing is not an option, then I'd scrape the popcorn and call it a day.


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## msmorales (Jun 26, 2011)

*I was afraid of that*

This all makes a lot of sense. Too bad I had the roof redone 2 years ago. Well - it sure makes this project easier. I'll just remove the popcorn and wait until I win the lottery and raise the roof! Thanks very much Rodeo and Stanchek, I appreciate it.


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## federer (Aug 20, 2010)

yea i have sort of the same issue. flat roof and just tore down the drywall ceiling. with only about 10inches of rafters to work with we are using spray foam. then drywalling back. i imagine this is the best option?


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## Perry525 (Jan 10, 2010)

msmorales said:


> This all makes a lot of sense. wait until I win the lottery and raise the roof! Thanks very much Rodeo and Stanchek, I appreciate it.


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You don't have to take the roof off to insulate above it.
Polystyrene is waterproof, wind proof and its not effected by ice.
You can lay sheets of polystyrene on the roof, cover them with waterproof plywood and then a layer of small stones about three inches thick. The stones will protect the plywood from blowing away and being killed by the sun.
As you can walk on polystyrene floor grade you can also cover it with Firestone rubber, a one piece made to measure waterproof roof. 
Polystyrene will remove the direct contact between the sun and the inside of your home making it a lot cooler. Any thickness will help, but eight inches will do the best.


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## Stanchek (May 1, 2011)

Perry525 said:


> ================
> You don't have to take the roof off to insulate above it.
> Polystyrene is waterproof, wind proof and its not effected by ice.
> You can lay sheets of polystyrene on the roof, cover them with waterproof plywood and then a layer of small stones about three inches thick. The stones will protect the plywood from blowing away and being killed by the sun.
> ...


Good point, but you should watch out for the weight of the roof per the expanse of the rafters.


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