Although I'm not really a fan of either TPO or PVC, I have to grudgingly admit PVC has a better reputation for lasting a long time.
What I might recommend, rather than replacing your roof on the pitched side, is to consider a non-vented attic. This is done by putting the insulation in the rafters instead of laying it on the attic floor. This way the attic becomes a conditioned space, so your ductwork is now inside.
- This is a delicate operation, though, because you do not want to develop an area where moisture is trapped between the roof and the insulation. This can reduce the life of your roof.
- There are several foam products (mainly closed cell insulation) on the market that address this concern, but they can be rather expensive.
I recommend finding a local home foam insulation installer who understands the issue and knows how to install the right product properly. I first learned of this concept from Building Science Corporation and have used it successfully in Southern California.
Another option is to add insulation above the roof sheathing prior to installing a new roof.
- A good reflective and high-R-value insulation placed to resist heat before it ever gets into the attic is extremely effective.
- Again, an experienced installer will use details that prevent roof decay caused by the moisture of trapped air and condensation.
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