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Nailable insulated roof sheathing in Zone 1-2

buma | Posted in General Questions on

Is unvented nailable insulated roof sheathing applicable in southern Florida?

From the top down the proposed assembly is:
1.  Concrete tile, foam-adhered to
2.  SBS granular surface  modified bitumen cap sheet, hot-mopped to a base layer of #30 asphalt saturated felt, on
3.  Plywood-faced composite nailable polyiso insulation, screw-fastened to
4.  3/4″ plywood structural sheathing on wood framing.
5.  The interior finish of the cathedral ceiling is pecky cypress. I do not know whether there is any layer between the underside of the structural sheathing and the cypress interior finish.

This is a roof-replacement project for a guest house built 12 years ago. The plywood top of the nailable insulation is rotted in some areas, but a consultant has concluded that the water intrusion is due to leaks, the source of which was an ill-advised ridge detail, courtesy of the original architect. The infamous ridge detail will not be part of the redo. But was the composite insulation doomed to rot anyway? What could be done to lessen the chance of rot in the insulation panels?

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  1. Expert Member
    Peter Yost | | #1

    Yes, an unvented so-called "hot-roof" is suited to your climate/location.

    If you have retained a consultant, have him or her create details/specs/contractor scopes of work to ensure you have a continuous bulk water and air control layer for your new roof assembly.


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