I am building a porch roof over an existing patio. The rafters are fabricated I-beams. I plan on putting aluminum soffit under the I-beams. On top of the roof I would like to put down a metal roof. I already put down 3/4" OSB and a rain/ice barrier. Do I need insulation and/or ventilation on top of the rain and ice barrier, or can I get away without it?
You don't need insulation for this application. If you haven't purchased the metal yet I would recommend looking for a standing seam roof system that the panel does not come in contact with the substrate and does not use exposed fasteners. If in the future you did decide to enclose the porch and add heat you could insulate the ceiling and leave an air space under the decking that could be ventilated from the eave to the ridge. A cold roof assembly with proper ventilation will dramatically reduce the potential of the metal panels sweating.
the ribs in the metal roof will ventilate it - insulation is only necessary if you plan to heat it
Its a outside patio, are you going to enclose it for living space? If not don't bother to insulate and for ventilation there is soffit that comes with vent holes in it. Add; no it will not cause a moisture problem, i had a patio with a open bottom metal roof and had no problems and i live in Florida.
