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  1. GBA Editor
    Martin Holladay | | #1

    In the 1990s, there were reports of expanding polyiso sheets that caused raised ridges on roofing jobs. According to polyiso manufacturers, that problem has been solved.

    More common are reports of shrinking rigid foam -- especially XPS. As with the "expanding polyiso" story, the result of the "shrinking XPS" story was a chorus from the manufacturers: "The problem has been solved."

    I say, butt the sheets of rigid foam tightly together, and tape the seams.

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