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Community and Q&A

Roof membrane in ceiling?

BryanD14 | Posted in Green Products and Materials on

In a commercial application we are putting a new floor over an existing roof that has an EPDM or TPO roof membrane on it. We feel this membrane should be removed for a variety of reasons, but, are getting questions from builders if it’s necessary. If left, it would above a dropped ceiling, below the new floor deck. Is there a code addressing this or literature backing up it’s removal? Thank you.

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  1. GBA Editor
    Martin Holladay | | #1

    What do you mean by "putting a new floor"? Do you mean a concrete slab?

    Do you mean floor joists with plywood subflooring?

    Do you mean flooring (carpeting or vinyl tiles)?

    -- Martin Holladay

  2. BryanD14 | | #2

    we have existing bar joists with a roof membrane on it. outside walls will get 'knee walls" to support new bar joists with metal deck and concrete floor above. we're leaving the existing roof structure in place

  3. GBA Editor
    Martin Holladay | | #3

    So you have existing bar joists. The membrane must be on something -- probably over a cover board and rigid foam insulation and steel decking or OSB decking, although you don't mention those existing layers.

    You need to tell us more. Where is the building located -- its geographical location or climate zone?

    What type of insulation is there now?

    Where is the insulation?

    What is the thickness (or R-value) of the existing insulation?

  4. BryanD14 | | #4

    building is outside of Philadelphia. no demo has taken place yet attached is a detail from the original construction documents.

  5. GBA Editor
    Martin Holladay | | #5

    Is an architect involved? Are the owners attempting to install insulation that meets code requirements?

    Your sketch shows that the existing rigid foam insulation is 3 inches thick. It has an R-value that is somewhere between R-12 and R-18. That's not much.

    The existing insulation is a vapor barrier. So is the steel decking. So having a third vapor barrier (the existing membrane roofing) doesn't change the vapor permeance of the stack-up one way or another.

    It's already a vapor barrier, with or without the roofing membrane.

    Before we can give you advice, however, you have to tell us the plan for new insulation -- if any.

    -- Martin Holladay

  6. BryanD14 | | #6

    that's the assembly were 'encapsulating'. it's the as-built condition. our concern is off gassing and mold when we put the new roof structure above it. attached detail may clear it up. (new construction above)

  7. GBA Editor
    Martin Holladay | | #7

    Bryand 14,
    I don't see why there would be any mold concerns. You can't get mold without moisture, and both sides of this assembly should stay dry.

    Off-gassing will be much less once there is no sun shining on the roofing membrane. That said, it's hard to evaluate the off-gassing issue -- especially since you don't even know what kind of roofing is there. (You called it "EPDM or TPO.")

    The problem with making recommendations in response to off-gassing questions is that some people are chemically sensitive. If there are chemically sensitive occupants, all bets are off. It's certainly true that most roofing products aren't intended to be installed indoors.

    -- Martin Holladay

  8. BryanD14 | | #8

    The roof was recently replaced (5-10 years) I can find out the material, but, sounds like there is no clear evidence that it should be removed. thanks for your insight.

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