preparation for new metal roof over old roof
Can I put rigid insulation panels over my existing asphalt roof (with 1×4 strapping between panels) and attach new metal roof right overtop? There is no attic so it seems like the easiest way to add R value.
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was told by roof supplier to put down fanfold and apply metal over that.fanfold doesn't like to be exposed to elements too long ,so cover it fairly quickly
My house has one roof section that is very low slope, no attic. It had been covered in torch down then some sort of fiberglass membrane. It wasn't leaking when we bought the house, but I was pretty sure it had done so in its past. So when we remodeled, I couldn't wait to finally apply new roofing material. I was very eager to have the contractor tear everything off to the sheathing so I could get a good look at it. Sure enough, there was some minor rot but it needed fixing. There's no way that I'd cover over any part of an older house that may be structurally compromised. In your case, the added work/cost of stripping the roof is minor compared to the overall cost of a new metal roof. And the peace of mind will be priceless.
By the way... 1x4 strapping will allow you to add an insignificant amount of additional insulation.