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Community and Q&A

Best insulation method for new construction, 3-ply flat roof in Central Florida?

Kimberly N | Posted in Energy Efficiency and Durability on

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.

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  1. Aj Builder, Upstate NY Zone 6a | | #1

    Kimberly, how can you be building without permitted, detailed, stamped plans? And contracts with all the dozen subs?

    Insulation? Start by calling insulation companies and visit contractors at their site and see who is the preferred guys and how the best contractors are building flat roof homes. You have the wrong project manager if all this is unknown and you already are started.

  2. User avatar
    Armando Cobo | | #2

    It's simple, install a good moisture barrier over your roof sheathing, then 4”-6” rigid foam insulation, and then your roofing material, like it is done on commercial buildings every day. That will allow all duct work, plumbing and electrical (including can lights) to be in the conditioned space. We often use this type of roofing in SW Pueblo Architecture.
    Heat-torch applied bituminous membranes are most popular; however, PVC is better and white in color, so it has good reflectance and it will save on your energy bills. Make sure you have good drainage as well.

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