Standing Seam Installation question

Jim Fillerup
3/6/2014
I have been trying to obtain a definitive answer to this question and have contacted several people, but none have provided me with an answer. Here is the situation: We have a building under construction that has steel roof trusses and has a structural metal deck ( 1-1/2" B type deck with ribs and grooves) installed over the trusses. The structural deck was necessary for seismic purposes. The ribs and grooves run perpendicular to the slope of the roof, which is 3:12. The attic is a ventilated cold attic. We would like to install a standing seam metal roof over the structural deck. The question or questions are: Can we install the standing seam roofing directly over the structural deck? Or, do we have to provide an additional sub-straight sheathing over the structural metal deck, which will really add to the cost? And, do we need to provide a membrane over the structural deck like Kraft paper or ice and water shield? We are a little concerned about vapor collecting in the grooves of the structural deck if we install the standing seam over it. Do you see any condensation problems? Hope you understand my questions and hope I can obtain a definitive answer from an expert. Thanks, Jim
David Stermer
3/7/2014
Jim, Thanks for the metal roofing question! It is possible to imagine a situation where the assembly that you described would perform adequately. However, it is not typical practice. The concerns I would have are condensation, low insulation and noise. If the roof is cold and there is warm moist air inside, there will be condensation, potentially above and below the structural deck. If the air inside the building is conditioned, insulation is needed to maintain that conditioning. Standing seam metal roof panels typically have lines of attachment separated by flat areas of the panel. Under relatively low wind speeds, the flat of the panel can flutter causing objectionable noise, especially if immediately adjacent to bare metal supports. Depending on the code/specification requirements along with the use of the building, insulation and a moisture barrier may be needed to assure acceptable performance. Regards, David Stermer
Guest User
3/7/2014
The attic is a cold attic and is ventilated. So the underside od the structural deck should remain close to the same temperature as the outside. We are just searching for a definitive answer whether we can or cannot attach the standing seam directly to the structural deck. And do we need any type of underlayment between the standing seam and the structural deck? Thank you for all of your help and opinion.
David Stermer
3/7/2014
Jim, Standing seam panels can certainly be installed directly to structural decking. It is common to add an underlayment for another level of protection as well as noise dampening. Regards, David Stermer
David Carbone
7/13/2015
Hi Im planning on putting a standard seam metal roof on my house. I have asphalt shingles 2 layers on there now. I was told by the contractor they can put the roofing over the 2 layers that are on there after they take the high spots off the existing ones and cover the roof with a membrane material but if they do go over the two layers then it will void the warrantee of the metal on the roof. But if they went over one layer then it would be warrantied or if it was totally stripped the metal would be warrantied also . My question why would it be warrantee with one but not 2? Can some one explain this.
Todd Miller
Isaiah Industries, Inc.
7/13/2015
David, in all cases you should receive a printed warranty to inspect. What they are telling you does not make sense to me either and I have not heard of a warranty like that. Now, that said, building codes, where they are in effect, usually require no more than two layers of roofing on a structure so there may be some confusion with that.

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