We are building a new home in Central Florida – hot and humid weather. Home is 2 story, CBU on 1st floor and 2 x 6 frame on second story. We have a very low pitch, commercial grade flat roof with 2 ft overhangs. There is only about 2 ft space in the trusses and much of that is filled with A/C ductwork. The builder had planned on R-39 blown-in, but now realizes this will be very difficult to get in the space properly, and then vented soffits are going to allow wind drift of the insulation. After reading here, we’ve decided on non-vented soffits since we have a flat roof.

He is very reluctant to use closed cell foam spray because of potential water leaks from the roof and humidity issues causing moisture and mold in the attic space. He’s somewhat open to open-cell foam because he feels leaks would at least get through the foam and present themselves on the interior somewhere. We are in a hurricane zone, so I like the thought of extra rigidity from the closed-cell foam.

I am completely at a loss on the best way to insulate our house now! It is going to be very difficult to access the attic area after drywall to fix any future problems. I like the idea of the attic-space being sealed for the a/c duct-work.

Would it be appropriate to foam on top of the new 3-ply roof system (thus moving the vapor point on top of the roof and not in our attic space or would this present different problems? Am I even understanding all these issues correctly??

Any insulation issues I should consider for the upstairs walls? Currently, we are planning on R-19 batting on 2 x 6 walls, or possibly flash & batt if we have the funds for it (and advisable).

I feel like I’m getting a PhD in construction building this house and trying to make the correct (but affordable) choices. This is our forever house, and any advice you can give us would be VERY appreciated.