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I hoping to find out information on the best insulation products and methods for insulating our home addition, which is currently under construction here in Tallahassee, Florida.

We have a low slope (1.5' to 12') modified bitumen (rolled type) roof,
with 10 ' cathedral type ceilings with 2'x8' joists serving as the roof
rafters/trusses and are planning to put the 2.5" of "closed cell"
(Specificallly were are looking at a higher density product brand named
"Airtight") foam insulation between the joists and also an appropriate
layer of the same "closed cell" foam insulation in the outside wall
cavities also. The company who made the best sales pitch and we are
thinking of using is GA Foam Solutions based in Albany, GA, and
servicing our area and the big bend.

An acquaintance said a series of studies were done involving homes in the central florida area, built by Habitat for Humanity that involved research on this type product, vs the "open cell" foam (aka Icynene and other such
products) kind of product and that the Icynene product performed much
better because the "closed cell" foam had caused the plywood roof
sheathing plies to separate after 5 years as well as the "closed cell"
foam itself had disintegrated because of some kind of heat build up
(typical in the warmer climate of central Florida) and also that the
heat would cause the warranty on our new roof to be voided because of
this heat build up. I cannot find anything of this nature described online, and wonder if this person had been mis-informed perhaps by an open cell foam insulation salesperson.

We also plan to put the thin film solar collectors on part of this roof,
and are planning to coat the top side with a white elastomeric coating.

I'd love to know everything I can about all the various brands and densities of the polyurethane foam insulation used... for this purpose... also if any of you have any negative thoughts or knowledge of the "closed cell" insulation product. We are under the impression that the "open cell" contains no vapor barrier whereas the higher density "closed cell" is water
resistant and a vapor barrier. Also we've been told that as of Dec.
2008, the Florida building code will no longer allow the more spongy
product such as "Icynene" "open cell" to be put immediately on the
underside of a roof, because it is not vapor proof and it does hold
water like a sponge. This could be rumor also, that we were told by a closed cell salesperson :laughing:.

This is my first post, hope its ok.

1,186 Posts
This is all news to me.

I can tell you that closed cell is less likely to absorb moisture. I have used that for 35 years to store my camera gear and it is in mint condition.

In my vacation home where it gets to over 120 in the summer for days on end my closed cell foam is doing just fine. While I don't have the humidity that Florida has it seems to stand up to the heat pretty well.
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