Mobile home metal roof

Phil Lav
8/27/2016
I have a mobile home I am working on. The existing roofing system is basically a bunch of 2"x2" trusses 16oc with a metal roof directly on top of them - has about 3" of pitch. Had 2 layers of fiberglass insulation in there with a plastic layer on the ceiling side.. I am currently building new trusses with a 6/12 pitch, 1' overhang, and vaulted ceiling. They will be basically 2x4s with a collar tie 1/3 from top and a birds mouth at bottom - its only a 12' span. Anyways i am looking for advice on insulation and ventilation. I am thinking of just using 2x4 perlins and no roof deck to keep the weight down as close to the oem roof as possible. Would installing a 1 1/2 rigid foam between the perlins - kind of like a roof deck have any disadvantages? The metal roof will be a corrugated type like you would see on a barn.. Does this roof type need ventilation? What would be the best way to insulate the 4" of rafter space and ventilate if necessary.
Todd Miller
Classic Products, Inc.
8/28/2016
Thank you. The call for ventilation is regardless of the roof type -- required by code actually. However, the need does somewhat accelerate with metal as a metal roof can be cooler than other roofs, and hence a good candidate for condensation. Condensation occurs when warm, moist air originating inside the home strikes a cool surface. In your case, that would be the back of the metal roof. Was condensation an issue before? The options for eliminating condensation include insulation, vapor barriers (keeping the moisture inside the living space) and insulation. Make sure that the roof panels you buy are suitable for the application method you select. You want to be sure to note damage the vapor barrier (layer of plastic) that exists now. Also make sure that any vents, fans, etc from inside the living home vent all the way to the outside. To be safe, I would suggest trying to add ventilation in the newly created attic space. Insulation should be down on top of the structure rather than directly beneath the roof panels. I hope this helps.
Guest User
8/31/2016
Todd, what do you think about the rigid foam insulation between the perlins and then synthetic felt paper over the whole roof then the installation of the corrugated metal roof panels? - under the foam would be baffles or an air space then a fiberglass insulation with a vapor barrier on the ceiling side.
Todd Miller
Classic Products, Inc.
9/1/2016
Phil, that sounds reasonable. Make sure that the roofing manufacturer supports their product being installed in this way.

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