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Community and Q&A

Closed-cell spray foam roofing?

Barry_E | Posted in General Questions on

I’m finally having the suspended concrete floor sprayed underneath with closed cell foam. It has been a fight to keep the space comfortably heated while the floor would remain around 40 degrees Fahrenheit.

Speaking to the owner of the small company providing this service to me he said he had used closed cell foam on a rusted tin roof he had to seal it. He said he used some type of coating to keep the uv rays from causing it to deteriorate. He said he had done other roofs for locals externally and it seemed to be working well. I’m pretty happy with what he’s done under my  floating slab but I’m not sure he’s done the correct thing on these roofs. The big problem where I live is finding people who really do know what they’re talking about. To be honest it’s a hard area for a professional to make a living as it’s a rural area with lower income people.

Ive checked online and found that this is done on flat roofs. I have a flat roofed building that has the rubber membrane and is close to needing replaced. Is this something I should consider doing?  I don’t think the fellow I mentioned uses anything special for his roof coatings so I would contact someone else for this service or buy the equipment and start doing it myself.

What do you guys think about this system, it’s pros, cons?

Thanks in advance.   Barry

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Almost all 3lb density polyurethane foam roofing is blown with HFC blowing agents (soon to be banned under the Kigali amendment to the Montreal Protocol), that are extremely powerful green house gases. Three pound foam also has a very high polymer per R as an insulating material.

    On the plus side, it does seal well, and if protected from UV lasts a very long time, and it is displacing other, more temporary roofing materials. How it works out on a lifecycle material basis relative to other roofing depends on how well it is maintained. In flat roofs using stone ballast as the very durable UV protector works well in locations where the need to remove of snow loads are non-existent.

    If going this route, using the minimum amount necessary to achieve dew point control at the roof deck,( as outlined in TABLE R806.5 INSULATION FOR CONDENSATION CONTROL in the IRC) with open cell foam or fiber insulation fattening out the total R on the underside of the roof deck is the "greener" way to go. A single inch of spray roofing polyurethane (~R7) uses as much polymer as 6" of open cell foam (R22). Unlike roofing polyurethane, open cell foam is blown with H2O (water), a very low impact blowing agent.

    https://up.codes/viewer/utah/irc-2015/chapter/8/roof-ceiling-construction#R806.5

  2. Barry_E | | #2

    I believe under the roof deck is 2x6 or possibly 2x8 rafters, wooden lath strips, plaster then a drop ceiling with insulation batts on top of it. I don't know if that would cause any moisture problems? I'm really just interested in the roof covering but figured if I could get any r value it would be a bonus. This rubber membrane roofing hasn't lasted very long at all. Ten years at tops. Without talking to a professional I'm not sure what's next, patching or replacement?

    1. Expert Member
      Dana Dorsett | | #3

      More information is needed to make this call. Your location/climate zone matters, as does the ventilation (if any) to the outdoors in the space between the drop ceiling batts and the roof deck.

      Insulating on top of a vented roof doesn't usually add a lot of thermal performance.

  3. Barry_E | | #4

    I'm around 3000 feet elevation in the North Carolina mountains. I'm not sure what's zone that is. It gets cold here and we get snow but super rare for it to be heavy enough to need to remove it. I doubt it's ever been removed but I'm not 100% sure.

    I'd guess if there's any ventilation it's unintentional as I've seen nothing protruding through the deck.

  4. GBA Editor
    Martin Holladay | | #5

    Barry,
    Here are links to two articles with more information:

    "Spraying Polyurethane Foam Over an Existing Roof"

    "Roofing With Foam"

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