Moisture control and permiablity in CZ 4. A client is interested in a SIP roof as a retrofit for an older log home. Currently the plan is to strip the existing roof of asphalt and felt and repair as neede the existing osb. The build out calls for 1.) 30# felt 2.) 4-6" SIP panel nail board 3.) 30# felt 4.) High albedo standiing seam metal roof. Is the first layer of felt a potential moisture collection issue, would the system be better off without it?

I think people are having difficulty responding to your post because you have left out some key information about the existing roof assembly and are being a little cryptic about the location in only stating the climate zone.

Is the existing roof of this log home unvented timber frame or ventilated trusses, etc? (describe the assembly, it matters)

Also, 'nail base' isn't really a SIP, it's just insulated 'non structural' sheathing, so maybe you would want to post in the forum listed below to get your answers.

Green/Energy-Efficient Building and Construction
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