Unventilated porch roof

I agree, lack of ventilation is not the problem on your porch. I always recommend that homeowners use products that are certified by the Metal Construction Association and are installed by MRA listed contractors. You say you are located in coastal Maine, I am not sure your proximity to the sea, but I would recommend the use of an aluminum panel.

I’m considering a metal roof for a situation where an asphalt shingle roof has failed prematurely, and I’m hoping that you can tell me if metal roofs have ventilation requirements? I have a large outdoor, wrap-around, hip-roofed porch in southern Maine. The area of the porch is larger than the footprint of the house itself, and in the summer the sun beats down continuously on the sun-side of the roof. Although I’m in Maine, not Florida, our temperatures have been getting well into the 90s here, especially in July and August. There’s no ventilation whatsoever between the roof and the porch’s sloped bead-board ceiling because the bead board is nailed directly to the rafters. I’ve been told by contractors up here that they never ventilate these kinds of porch roofs. But I believe that the dozens of separate air-tight spaces created between the rafters have gotten so hot that this has been the cause of the shingles’ failing after just 4-5 years. I assume that because this is an outdoor porch, condensation on the underside of the metal would not be a problem. But what about the fact that there is no ventilation at all and no opportunity to put any in? I can’t find disqualifiers for lack of ventilation in the metal roof warranties I’ve looked at, although there are many such disqualifiers in the warranties for asphalt shingles. So I’m wondering if it’s okay to use a metal roof in my situation? brad board follows the slope