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#74040 by Aaron Ben-Avraham
Mon Jun 04, 2018 5:47 pm
Flat Roof terrace insulation over living area.

I'm a little out of my depth on this but I also want to learn how to best do this so here goes:

I have a client who wants to do a Flat Roof Terrace over living space. It is a fairly large area (~1000 Sq. Ft.).

He is probably going to use something like TufDeck, Duradek or IB DeckShield PVC as the waterproof walk-able nonslip deck surface.

The roofer he is talking with is advising him to do 6" polyiso on top of the Roof Deck for the insulation below the PVC Surface (60 mil PVC adhered over Densdeck Cover Board over 3/4" decking).

Will PolyISO covered with DensDeck and 3/4" Decking be OK as a traffic/pedestrian surface? I am a little hesitant about that. It will not be a very high traffic deck, but there will be times that the homeowner will have a number of people on the Roof Terrace for parties (I am way over specifying the TJI Joist to carry a significant load so that won't be an issue). Would one be able to possibly feel the PolyISO move or compress, especially if there are a number of people on the terrace?

My initial proposal was to simply use 3" of Closed Cell Spray Foam (CCSF) on the underside of the 3/4" roof decking (with the PVC surface adhered to the decking above) and then either use open cell below the CCSF or even batt insulation against the Closed Cell to get the proper R value (This is in Atlanta). The joist will be 18" deep so even after the insulation is installed above there will be plenty of Room for ducts, wiring, recessed lights, etc.

Also any thoughts on Using the PVC products mentioned above? Does anyone here have any experience (good or bad - especially bad) with these products? I was initially going to specify Rubber Pavers over TPO or EPDM (probably TPO) , which even now I still think would probably be less expensive than the PVC.


Many Thanks!
#74041 by joshhuggins
Mon Jun 04, 2018 6:22 pm
I would go with your solution or something similar. The nature of the foam just seems like it would break down over time and end up with a spongy floor system at the seams of the deck board that would accelerate issues with seams in the PVC Decking. If it was a roof that you knew would see really minimal traffic, maybe, but why go this route when it sounds like you clearly have the space to do a more traditional system with time tested materials.

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