Adding exterior roof insulation
jculbertson
| Posted in General Questions on
We are renovating a home in Redmond WA(4C). Roof rafters are not deep enough to provide sufficient insulation. I also want to add a thermal break. We’ll put 2 inches of spray foam in the rafter bays and top off with loose fill behind netting. Roof will be standing seam metal. Is there a way to get some rigid insulation on top of the roof deck?
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Replies
Yes. A number of manufactuers sell naibase panels, essentially an SIP panel with OSB only on one side. You can install this above and install your metal roof over it. Technically not rated for roofs, but you can also use one of the thicker ZipR panels.
If you go with enough exterior rigid, you can skip the interior sprayfoam completely. Might be a wash in overall cost without any of the risks of spray foam.
Not sure how the numbers add up, but also worth looking at rigid foam and roof sheathing (plywood/OSB) if the nailbase or ZipR is cost prohibitive.
I did this when I converted my garage to office space and worked well.