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How to detect a roof leak after having the underside of the roof deck sprayed with closed-cell foam?

cheezlo | Posted in General Questions on

I live in Buffalo, NY, and am renovating a Cape Cod style home. The interior is completely gutted and had a roof tear off and GAF system installed with no ventilation, with the plans for having the deck sprayed with closed cell. I had a question that no one up here can answer…

As the roof fails or if there is some sort of damage, how will I know if the underside is 100% sealed? My fear is the water will rot the rood substructure and hold mold. Is there any way to create a path for any potential leaks to follow??


  1. Donald Endsley | | #1

    The expensive option is to fir out a 2" ventilation channel between the insulation and the roof deck, assuming you have the ridge vent part of the GAF system installed, and if not add the ridge vent in, and ensure you have enough venting at the eaves.

    If the roof is leaking it is rotting. It doesn't matter if there is a path for the water to follow or not. The only way to delay or reduce the damage is to have drying potential. With closed cell on the bottom of the roof deck and asphalt on top you won't really have any. But that's not the real reason to vent your roof. The real reason is Ice dams. In Buffalo you get Lake Effect Snow, so you have a fairly high snow load. That Snow acts as insulation warming the bottom of the snow (because your roof is putting out energy) by having a ridge vent, eave vents, and an air channel between roof deck and insulation, you will hopefully keep your roof deck cool enough to prevent the bottom of the snow from melting and thus preventing Ice dams.

    1. Ecological_Culture | | #6

      If you have "ice and water shield" membrane, is ice damming a problem?
      I expect the shingles would suffer, but anything else?

  2. GBA Editor
    Martin Holladay | | #2

    Eventually, all roofs leak. If your roof eventually develops a leak, you will know it. The first sign is usually a stain on your ceiling.

    These facts are true whether or not your roof sheathing has been sprayed with closed-cell foam.

    If you were the type of homeowner who was obsessed with roof leaks -- or if you were a roofer -- you might have chosen to live in a house with a ventilated unconditioned attic. That type of house has one advantage over the type of house you are living in: you can always climb up into the attic and inspect the underside of the roof sheathing.

    Donald's advice is good. If you want to include a ventilation channel under your roof sheathing, you can. But that doesn't mean that your roof won't eventually leak. It doesn't even mean that you'll discover the roof leak any faster.

    -- Martin Holladay

  3. cheezlo | | #3

    Thanks for the replies. The house has an original attic, but I am vaulting some ceiling areas. I consider myself somewhat of an expert on ice dams and the importance of roof ventilation, but the roofer and the insulation installer are telling me I wont need ANY with the closed cell. I wasn't comfortable with that advise so i am reaching out for opinions. So all thoughts are appreciated...

  4. GBA Editor
    Martin Holladay | | #4

    If you haven't read it yet, you may want to read this article: How to Build an Insulated Cathedral Ceiling.

    -- Martin Holladay

  5. Anon3 | | #5

    You can't. There's a reason the big tract builders stopped offering foam as an option after they tried it out.

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