Mark Homan
I have a 45 year old Ag shed that I converted to a shop. It has a 1:12 pitch roof and is covered by corrugated metal which is in good shape. They used nails to hold down the metal, but the put them in the valleys of the corrugated roofing which now leaks when it rains. I am going to cover the roof with another layer of metal using 1x4 strips of pine as purling. Roof joist is 2x6 in a lean to construction and there is not attic space. I used plastic for a vapor barrier on the warm side and then installed some Styrofoam for insulation. I would like to install the new metal over the old and put down felt as a moister barrier over the old roof. Instead of felt, do you think something like a solar guard reflective barrier would be better?
Todd Miller
Isaiah Industries, Inc.
I do not have a lot of experience with metal over metal installations. There is a company called RoofHugger which makes purlins specific to this purpose but I think they work more with large commercial roofs. To me, the biggest risk is if the two metals start expanding and contracting at different rates, putting add stresses on the fasteners. That would be a biog concern to me. Something like a reflective barrier between the two might contribute to that happening. What would I honestly do? Probably tear off the existing, put down underlayment and then vertical battens followed by horizontal battens, and then ventilate this area between the new metal and the foam. Make sure that the new metal is suitable for a roof of this extreme low pitch -- check with the manufacturer.
Guest User
Mark, I am looking at a similar situation. I have a 200' x 100' municipal garage that we want to re-roof. We don't want to tear off the old roof as it has sprayed on insulation directly applied to the underside. We also don't want to over load the existing metal trusses. Our plan was to use 26 gauge metal roofing and 1" x 4" purlins to build a roof over a roof. We were going to vent the facia and instal a ridge vent. I am looking for advice and expertise.
Allan Reid
Dura-Loc Roofing Systems, Inc.
Go to Roof Hugger as they make profiled purlins to go over existing roofing and should be able to help. Ask for Dale and said Al sent you.
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