Occupied Roof: paver system over low slope TPO and polyiso insulation

[benjamin_eb]

Hello friends, I have a question about an occupied roof paver system on a low slope tpo assembly.
The basics:
Type IIB building.
Two floors are Business occupancy, 10,800 sqft per floor.
Roof (the third floor, the highest floor) is partially occupied, Assembly occupancy 3,800 sqft.
We have designed a paver system on pedestals, on top of a low slope tpo roof over polyiso insulation.
The insulation is proposed as Firestone ISO 95+ GL.
A 1/4" Densdeck will go over the polyiso, with the single ply tpo on the Densdeck.
Then a pedestal system is on top of the tpo, with pavers.
My question is, what do we need to consider regarding flammability and fire safety? The polyiso is a flammable product (flame spread 50, smoke developed 160-180). The Densdeck provides a barrier over that, so that's a good thing. Is this assembly acceptable? Can anyone identify potential problems?
Thanks for any input!

 

[Yikes]

First of all, welcome to the forum!

Secondly, even in non-combustible contraction such as Type I and Type II buildings, combustible Class A, B, and C roof membranes are allowed by 2019 IBC 603.1, item 4. (See excerpt below.)
Check with your local jurisdiction to see if they have any code amendments top this. Many jurisdictions here in California want a Class A roof no matter what. TPO is available as a Class A roof.

I've installed the exact system you've described: pedestal pavers on TPO. That was a Type V-A building.

 

[benjamin_eb]

First of all, welcome to the forum!

Secondly, even in non-combustible contraction such as Type I and Type II buildings, combustible Class A, B, and C roof membranes are allowed by 2019 IBC 603.1, item 4. (See excerpt below.)
Check with your local jurisdiction to see if they have any code amendments top this. Many jurisdictions here in California want a Class A roof no matter what. TPO is available as a Class A roof.

I've installed the exact system you've described: pedestal pavers on TPO. That was a Type V-A building.

View attachment 8228

Thanks Yikes! Good info. It's always helpful to hear that others have installed similar systems.
One other question I have is, what about separating the polyiso from the floor? A 1/2" gypsum thermal barrier is "generally" required as stated in 2603.4. The roof installer has proposed 1/4" Densdeck, but I'm thinking 1/2" would be required based on that code language. Does that sound correct?

 

[Tim Mailloux]

Thanks Yikes! Good info. It's always helpful to hear that others have installed similar systems.
One other question I have is, what about separating the polyiso from the floor? A 1/2" gypsum thermal barrier is "generally" required as stated in 2603.4. The roof installer has proposed 1/4" Densdeck, but I'm thinking 1/2" would be required based on that code language. Does that sound correct?

I know that EPS and XPS insualtion can require thermal barriers, but I didn't think poly-Iso required one.

 

[benjamin_eb]

I know that EPS and XPS insualtion can require thermal barriers, but I didn't think poly-Iso required one.

It's my understanding that all foam plastics fall under Chapter 26. So yes, I believe polyiso would fall in that category and therefore require a thermal barrier (and must follow the other requirements of that chapter).

 

[Yikes]

I don't remember, it's been a while. But you can ask your roofing technical rep, especially if it's one of the big firms like Johns-Manville.

 

[Tim Mailloux]

U just went thru this with a roofing rep (JM) bit didnt verify it with the code. I was told the ESP & XPS insulation require thermal / ingnition barriers betweent the metal deck and insulation, but Poly-iso does not require one. FWIW I only specify poly-iso roof insulation and I have never called for a thermal barrier. Currently there is a massive poly-iso shortage projected out until late winter / early spring and one of my projects under construction is looking to change from the specified poly-iso to XPS which is actually available. The rep informed me that if we made that change we would need to install a 1/2" thermal barrier on the metal deck per code.

 

[Paul Sweet]

IBC 2603.4 says "foam plastic shall be separated from the interior of a building by an approved thermal barrier ... ". Tile or concrete pavers should make it a Class A assembly.