This is a big area of discussion between contractors, insulators, and building science people.
First there are two types of insulating foam used.
Open cell and closed cell.
The open cell will let water through. And it is is lower R value so that it take more foam.
And in the very coldest climates (I think colder than 7500 heating degree days) it requires a vapor retarder, but that can be handled by painting it.
But in reality roof leaks or not that much of problem if the roof is done correctly with the right flashing etc.
I am not sure what I would do.
On new construction I would do anything possible to keep HVAC and ducts out of an unconditioned space. Either put them in different place, foam the roof or use SIPS for the roof.
The more cutup a roof the more possibility of leaks.
I would have to do some shopping before deciding to do that on a retrofit.
And part of that would be getting a quote from a GOOD HVAC contactor (find one that will do a duct blaster test) to seal and insulate the ducts and the HVAC where possible.
Sorry, but I can't give you an absolute yes or no. |
Member Since
04/26/2005
Total Contributions
3644 Posts
|
Moderated by cellarwater 
