We are building a barn-house and using SIP (Structured Insulated Panel) on the roof. We are getting conflicting information with respect to the roofing over the panels. Is it OK to put roofing directly on top of the roof panels (ie, standing seam roof) or do we need to add furring and an additional layer of plywood prior to applying the roofing (in order to have a vent space)?
signed,
“Good But Cheap” Builder
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Replies
The only concern I'm aware of regarding roofing over SIPs is with some asphalt shingles failing prematurely because the heat is not absorbed by a vented attic space but is reflected directly back into the shingles. A metal roof over SIPs might expand and contract a little more than one over a vented attic space but it should withstand the hotter surface temps with no problem.
One other reason furring strips are occasionally recommended on metal over SIP roofs is that they give the fasteners a little more meat to hang on to. It should be no problem attaching directly to the OSB skin with metal however. Most guys that add the furring do it as an extra precaution only. In my opinion it's not a bad idea, particularly since the additional movement in the metal will probably stress those fasteners a little more than it would over a more traditional roof only. The resulting ventilation would be an added bonus.
Follow the specific recommendation of your SIP supplier and you should have no problems with standing seam in this application.
Kevin Halliburton
"I believe that architecture is a pragmatic art. To become art it must be built on a foundation of necessity." - I.M. Pei -