Foam board under exposed fastener metal roofing
Badgerfan
| Posted in General Questions on
Looking to build a 30×40 garage with 2×4 walls and using the exposed fastener metal roofing. I understand standing seam would be better but thought maybe it would be better to pay for the extra labor for the insulation up there and cheaper metal roof. Is it worth it to try and insulate ontop of the roof deck with foam board? This will be heated with only in floor radiant. If so, what steps do you like to see for the roof deck layers? This is in WI.
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Replies
I wouldn't install the roofing directly over the foam, but if you install horizontal sleepers first it would probably be ok.
Thanks Michael. I reached out to Midwest manufacturing for the Menards brand, and they said to install it directly to the foam board. They said the cold air under it from the 1x3 would cause issues. Which seems odd.
The cost to do so must not be really worth it as I haven’t found really any garages with foam board on the roof deck with metal roof.
Badgerfan,
Exposed fastener roofs rely on having a solid substrate to maintain the pressure on the screw gaskets to keep out water. The foam underneath may compress and allow leaks. I'm surprised the manufacturer was onside with it.
Here is what I did a while back (Post #2):
https://www.greenbuildingadvisor.com/question/pnw-garage-studio-build
You can use any size 2x on edge to get the R value you need and the insulation between them can be either rigid or fluffy. The roofing gets screwed into the 2x so you are not compressing any foam.