cathedral ceiling - no attic space

thomas greimel
1/15/2014
I have a roof with no attic space in the living room and experience radiant heat coming through the ceiling in the summer. My roofing contractor can install shingles and add more insulation on that portion of the roof but the cost is high. Would it make more sense to just install a metal roof to prevent the radiant heat penetration? My concern is that the metal roof may also conduct heat downward in the area of the cathedral ceiling and thus nullify its benefit as a radiant barrier. I know from experience that metal conducts heat downward since we have metal awnings (aluminum) that are not insulated and when the sun hits the awnings you can feel the heat below.
Todd Miller
Classic Products, Inc.
1/15/2014
Really, Thomas, anything is better than nothing. A metal roof in a light color or with a reflective coating would be helpful. Is there any way you can add a vented airspace? Frankly, a vented thermal brake like that will be your best bang for the buck, regardless of the roofing material you choose. Adding some insulation to it would also be helpful. But this will require either cross battening and a metal roof on battens, or else a new layer of decking. There is also a product available called ThermaDeck made in the metroplex which used in conjunction with construction like this provides an airspace and insulation. That may be of value to you as well.
thomas greimel
1/15/2014
Wrong, you misunderstood sir. I fully intend to have new roofing installed. The purpose of the question was to help decide if just metal roofing (without additional insulation) would be better than ashphalt shingles with radiant barrier and vented battened insulation. Cost is an issue with both options but especially with metal roofing.
Todd Miller
Classic Products, Inc.
1/15/2014
Sorry about that. A radiant barrier is effective only if it faces an airspace. To me, that's important to keep in mind. The reflective pigments in the coatings on Energy Star metal roofs help block radiant heat which is the heat that comes thjough your awnings. However, once the metal gets hot to the touch, it will conduct heat to anything it touches, which would be your underlayment and roof deck. This heat will continue to travel down into your house, depending upon how much thermal resistance it meets. Having an airspace would be very beneficial by stopping that conductive flow of heat. Asphalt shingles on the other hand block very little radiant heat and they still heat up, the same as metal, and conduct heat. So, the metal will be superior to shingles. If you can work in a radiant barrier that faces an airspace, that is good. If you can work in a vented airspace as a thermal break, that is even better, I'm not sure I am helping you. I hope I am.
Guest User
4/23/2015
Hello there:) Do I understand correctly that if I have a metal roof installed over my existing shingles without an extra air barrier, that it will make my house hotter in the summertime if the heat from the metal heats up the asphalt and radiates the heat downwards? My house gets really hot as it is in the summer, and I nearly freeze to death in the winter. I live 2 blocks from Lake Erie in Pennsylvania. It's like living next to an huge ice cube in the winter, and then in the dead of summer, unless I run my air conditioner 24/7 the temperature in my house gets up to 90 degrees. Below is a photograph of my roof. My contractor told me he would saw off my vent caps and cut a new ridge vent in the top of my roof for air to escape, but he never talked about this sheathing, or 1-2 inch air barrier that us recommended. He said he would put down some type of wood slats and to attaché the galvanized steel panels to. Would you be so kind to list in specific order how the installation process works for a standard two sided pitched roof I will discuss with my contractor before I hire them. Procedures: 1. 2. 3. 4. 5. Special Materials: 1. 2. Variables: 1. 2.
Todd Miller
Classic Products, Inc.
4/23/2015
Hi Lydia. Through special coatings and installation procedures, metal roofs will keep your home cooler in the summer by blocking heat transfer into your attic. The impact on your home in the winter is minimal as winter efficiency is achieved through insulation on top of your ceilings. Your contractor is referring to venting the attic which is a critical part of things for most homes. The strapping he is suggesting creates an airspace but it is usually not a well vented air space. If you can, please email me and I will reply with a number of links and documents and things that I think will be of interest to you. My email is [email protected]iller.com Thank you.

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