Re: What to use?????
From a design standpoint, corrugated galvanized steel roofing material would probably look pretty good.
If you have access to a sheet metal shop (such as an HVAC contractor might have), have some galvanized "Z" strips made up, 1" for each leg and the middle part of the Z. So 1", 90°, 1", 90°, 1". (Should be slightly thicker than the roofing; not sure what the ideal gauge would be.) The strips should be as wide as you plan to have the roofing. Place these horizontally on the wall and fasten the roofing to it (the corrugations will allow vertical airflow). You can use the same method to add a second layer of roofing, but for the second set of Z strips, offset them up at least 6" higher than the first set to prevent conductive heat transfer to the wall. This will provide at least 1" of space between the sheets and 1" of space from the inner sheet to the wall. The whole works will project about 3" from the wall.
I don't think insulation will be necessary, and may prevent proper airflow necessary to cool the space. My method above won't require cement board either.
By the way, galvanized metal should not be exposed to direct flame or extreme heat (over about 750 degrees) where people are present. Oxidation of zinc can release harmful gases. Don't used galvanized pipe on woodstoves.
(EDIT: If you search for the issue of using galvanized, pipe, you'll see a lot of "I've never had a problem with it" type of posts. That's an invalid argument. What is a valid argument is to understand that the melting point of zinc is around 780 F, at which temperature rapid oxidation begins to occur, and the melting point of zinc oxide is over 3500 F. However, vaporization and oxidation can occur at lower average temperatures due to absolute molecular energy, the same way a glass of water can evaporate at room temperature. Any time the pipe is hot enough to cause oxidation of zinc, it's hot enough to release harmful levels of zinc oxide vapor. For that matter, there is potential for release of zinc oxide vapor at room temperature, though at concentrations far below any cause for alarm.)
Last edited by Fencepost; 10-09-2013 at 05:10 PM.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.