Quote:
Originally Posted by dablack
Aluminum shingles would be great but way out of the budget. I will be going with a galvanized metal roof. That will give me the bright silver finish to reflect heat. With the air gap under it, I don't think I can beat it for the cost.
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One final note...
The above graphic was based in the work done in a study by Penn State, on the various modes of thermal transfer.
In the case of your roof, radiant heat will be the dominant mode, the left most graphic in the triptych.
So..........
The 'bright silver finish' of your metal roofing will loose much of its silvery brightness, and also reflectivity as time goes by.
On another thread I have been investigating Multi Layer Insulation that was developed by NASA.
The idea is that a reflective surface will reflect back a large percentage of the radiated heat that hits it.
The heat that gets through radiates on to the next layer, which will in turn reflect a percentage back, etc. etc. ... in NASA's case for up to 50 layers.
Now I know that your house will not be in orbit, but it will be subject to radiated heat energy just the same... so other reflective layers will do their job.
The graph above suggests the efficiency of heat radiated back vs. the numbers of layers.
As you can see, there is a very large improvement in the first layer, but not so much when you get to the 100th layer.
I think that when you get right down to it, aluminum foil, like you might use in the kitchen, is an extremely effective reflector, available at a commodity price.
Could make a pretty cheap 2nd reflective layer to go under under your metal outer roof.
-AC