SIPs Roof Replacement

user-1079879 | Posted in Green Building Techniques on January 4, 2012 05:11am

I have an energy makeover project for a client with an older log home. Beyond the usual infiltration issues we need to repair/upgrade the roof.

Current: asphalt shingle, tar paper, OSB in fair shape — some rot and rodent damage, but not past fixing.

One plan is to strip back to OSB, repair as needed, add tar paper, 4″ SIP Nail board, More tar and paper and a standing-seam metal roof ready for PV.

Thoughts? Ideas? Criticisms?

Thanks
b

Answer

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Martin Holladay | Jan 04, 2012 05:26pm | #1
Bruce,
Most 4-inch-thick SIPs have an R-value of R-15 or less. That's not much. What is the R-value of the existing roof assembly?

What's the climate?

For installation over an existing roof, you don't need SIPs. You can use nailbase, which has OSB on one side instead of two.
user-1079879 | Jan 04, 2012 06:10pm | #2
Existing R value is 19. Nail base SIPS was the intention already. I am concerned mostly with moisture as we are in Mixed-Humid East Tennessee, climate Zone 4. My SIPS supplier says the paper at the old roof, new nail-base SIPS joint is to eliminate moisture collection at that juncture. They use a liberal application of DEGA Seal at the joints and a Tar based seal in the nail-base OSB joint under the final layer of tar paper.
GBA Editor

Martin Holladay | Jan 05, 2012 08:21am | #3
Bruce,
If the existing roof is insulated with fiberglass batts, my guess is that the roof assembly is performing at significantly less than R-19. That means that your final improved roof will have a total R-value no more than R-34 -- and probably more like R-25 or R-30.

What I'm saying is, more foam is better.