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Why dont they half-lap SIP seams?

jmfb_k7 | Posted in Green Building Techniques on

Looking at potentially using SIP panels for an unvented cathedral roof, but read a bunch of stories about the seams failing for air sealing and then the OSB rotting out. Also the EPS shrinking and then leaving thermal gaps like what we saw on Joe Lstiburek’s roof where the foam was not overlapped. This got me thinking of why don’t they install them in a half-lapped fashion, cut one side of the SIP 6 or 12 inches short, along with half of the EPS, do the same with the next panel on the opposite side, and maybe add some acoustic caulk to each half-lap to provide an extra-tight seal. This way when the foam shrinks you still have overlap and it should be air-tight. There must be a reason they don’t do it that way already?

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  1. Expert Member


    I suspect it may have to do with the need for complete adhesion between the skin and foam for structural reasons, but I'm just guessing.

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