Flat roof (TPO over polyiso build-up) insulation guidance
I am trying to figure out the best insulation build up under this roof situation.
– 27’x29′ flat roof with 5/8″ plywood sheathing.
– There is polyiso over the plywood built up 1/4:12 on all four side to the the center. There is 1/4″ of ISO at the edges built up to approx. 3.5″ in the middle.
– There is no ice/water or vapor barrier under the ISO. The ISO is covered with 60mm TPO.
– The plywood seams where not tape or sealed
– The ceiling joists are 14″ TJI 360 at 16″ OC.
During the roof slope build up it was decided to use polyiso vs hand framing. The idea was that it would be a bit faster and cheaper to build up with polyiso and we’d also get the R from the polyiso.
However, the framing plans called for bird blocked venting down the joist bays with openings on the east & west side. So, I now have a polyiso sloped roof with outdoor air running underneath it.
After addressing some similar issues with another roof on the house on this thread here:
Metal shed roof – insulation schooling
I am now realizing that I have useless R over the roof and no real top side ventilation for the decking and don’t know how to address the interior insulation, interior vapor barrier build up, and how to protect the sheathing long term.
I did re-read this post, but I am still confused.
Thoughts, guidance? Thanks.
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