Radiant heat under dark colored ...: "Is there a way to figure out how much, and ..." - Dan Stein (9/11/2023) | Other

Is there a way to figure out how much, and how far, heat radiates from underneath an exposed (not insulated) metal roof panel?

I want to build a patio cover with a metal roof. The panels would be exposed underneath with no insulation. If I use a dark colored panel (a dark bronze color is preferable for aesthetic reasons) I need to know if you would feel heat radiating from the underside of the metal panels, and if so then how much? I realize it would feel warm if you held your hand close to the underside. But I am not sure how much, if any, radiant heat would be felt, say 2-3 feet below, in the habitable space.

The roof would be flat and sloping from about 8 feet to 9.5 feet high and open all sides, and typically there is a breeze. My question is, with the the metal roof panels at 170˚-180˚F (I’m guessing that’s how hot dark colored panels could get), would it feel like standing under an infrared heater? Or is 2-3 feet beneath too great a distance, with the panels at that temperature, for it to even be noticeable?

I’ve been scouring the internet for some time now, and made several phone calls to people in the metal roofing industry, with no luck. The only answer I seem to get is that darker colors are hotter in the sun. This makes sense of course. However, I won’t be lying on top of, or directly underneath the roof. It would be 2-3 feet overhead. I would like to use the dark colored panels, but the question remains for me: will they make the space uncomfortably warm, or would there be little practical difference between light and dark panels in this application?

Any guidance you could provide on the subject would be greatly appreciated.

Thanks, Dan

Dan Stein

9/11/2023

Thank you. I do not know any way to quantify an answer to your question. There's no doubt that a light colored roof would be cooler, and so would a dark colored roof that has reflective pigment in the paint. But, still, the metal will get hot and that warmth will radiate downward. Hot air rises so I think what you will find is the heat will build up throughout the day, forcing itself down to lower levels. A breeze could certainly blow it away but I think it's safe to say that on sunny days it will be a bit warm under there. I do have a metal patio cover on my house that is uninsulated. I'm in Ohio. I do not find the heat objectionable but my cover is a light ivory color on top. Somehow adding a thermal break or vented airspace between the surface and the underside would be helpful. Again, I don't know how to quantify this. It will be warm on sunny days. Will it be a burning furnace though? Not in my experience nor in anything I have heard in the past.

Todd Miller
Isaiah Industries, Inc.

9/16/2023

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Radiant heat under dark colored metal roof?