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Vapor retarder recommendation on low-sloped reroof

Matthew_Hanks | Posted in General Questions on

Hi there,

I’m re-roofing a home in Colorado Springs (zone 5) that was built entirely with cathedral ceilings with 2×10 rafter on a 1:12 pitch.  There is no attic (bottom of rafters are sheet rocked and I’m assuming the batt insulation in between the rafters is around an R-27-R30.  At some point the modified roof was replaced with EPDM over 1″ of foam.  Since then there have been condensation issues.  I’m proposing that we remove the existing roof system down to the decking.  Re-deck over the soft decking with 7/16″ OSB, installing 4″ ISO board, then 1/4″ Densdeck with a white TPO roof system.
I have two questions:
1) I’m reading about the need for a vapor barrier and am wondering if putting 6mil poly between the new OSB and the ISO board would be a good way to handle that?  I’m also willing to put Ice & Water in its place which would catch any moisture coming off of the TPO and allow it to make its way out to the fascia, but am wondering if that might be over kill or cause other issues with materials interacting negatively.
2) The homeowners biggest complaint with the EPDM system was all the noise it made while expanding and contracting.  Will TPO be less of an issue with this?  Are there other measures to take to help with this (ie – install 4×4 ISO instead of 4×8? …add a TPO weldable vent to each roof plane??)

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