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Low slope roof detail

7echo | Posted in General Questions on

I am re-roofing soon and have a question about whether to tape the seams of the polyiso boards.

  The current roof is 1″ in 12″, 3/4″ plywood deck, 30lb felt, ruberoid torch down modified. I will be installing 3″ of polyiso on top of the existing assembly and covering with fully adhered 60 mil TPO. Do the insulation board seams have to be taped? If it is determined that the seams are to be taped what tape should be used?

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  1. Expert Member
    Peter Yost | | #1

    HI David -

    If the rigid insulation is your continuous air control layer, the yes, all seams and perimeters need to be taped. If your new rigid insulation is more than one layer, stagger joints as well as tape them.

    Both Martin Holladay and I of GBA have done quite a bit of field-testing of tapes (search GBA for "tape test").

    In my experience, the acrylic adhesive tapes tend to be the best BUT unless you can get a tape manufacturer to vouch for the compatibility of your selected tape and the substrates to which your tape will be applied, you probably should do a bit of your own tape testing.


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