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Old 03-27-2008, 12:35 PM   #1 (permalink)
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Aluminum foil roof?

Every year here in Arizona the temperatures soar in the summer time to around 120F. The heat is just as much from the sunlight as it is from the ambient heat in the air.

So here's my question:
if i were to roll out and staple down some shinny aluminum foil on my roof - the entire roof - then would that reflect heat out or would the foil only heat up after just a couple of hours and bake the house?

getting enough aluminum foil from the $1 store to do the whole roof would only cost me between $20 and $40.

(but it's probably piss off the neighbors because they'd get even more glare on their windows.)

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Old 03-27-2008, 02:03 PM   #2 (permalink)
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It should take the radiant heat load off

A more attractive method is to use something like a privacy screen that surrounds the house (not like a fence to keep people out - it would need to be relatively close to cast a shadow) or planting for shade. But, that doesn't handle the roof....

But you're not limited to foil - any opaque radiant barrier will work....
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Old 03-27-2008, 02:06 PM   #3 (permalink)
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What happens when the foil starts ripping and blowing away in the wind? Foil isnt very strong. Maybe try some sheet metal?

Might as well just have an old tin roof.
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Old 03-27-2008, 02:13 PM   #4 (permalink)
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Quote:
Originally Posted by bhazard View Post
What happens when the foil starts ripping and blowing away in the wind?
Meh, that's just a practical concern
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Old 03-27-2008, 02:29 PM   #5 (permalink)
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Planting for shade:
In this part of Arizona it takes a lot of time and money to get trees to a good height.
There's money for buying, time for planing, money and time to water enough to grow a good size tree in the desert.

Shade Screen:
A Shade screen wouldn't get the roof and the expense would be much higher than just simply buying aluminum foil and using my staple gun to shingle them on the roof.

what about the ''Oven Effect" though?
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Old 03-27-2008, 03:06 PM   #6 (permalink)
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do'h - you're in AZ.... Planting isn't the greatest of options....

Oven effect.... Ovens work on radiant heat and natural convection... You'll be losing the natural convection (for the most part) but you'll be drastically reducing your radiant heat. If you have one...

Get a meat probe and stick it on your roof and cover it with some foil. Measure the instant temperature. As the roof has had time to get up to temp - that value will be how hot your roof gets without a cover.

Unfortunately, without going full scale (due to conduction), I don't think you'll be able to get a temperature with the foil covering your roof.

-----
The more traditional alternative is to install an attic fan with a thermostat. Blow out the air and try to keep the air temperature in your attic close to ambient. The one my parents installed in their home (South Florida) cost somewhere between $50-$75. slightly more than foil - but it won't blow away in a dust storm and is more aesthetically pleasing for you and your neighbors.

Even cheaper (maybe?) is foam roof channel stuff at your local mega home improvement place o.0 It installs the full length of the roof from base to top in the attic and creates a natural chimney effect - but you'll need a way to vent that heat near your roof's ridge...
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Old 03-27-2008, 03:20 PM   #7 (permalink)
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Thanks for the input, guys.
I'll discuss these ideas with my wife when she gets home and - if we decide to try anything at all - then i'll let you know how the bill changes compared to last year.
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Old 03-27-2008, 03:41 PM   #8 (permalink)
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Try the perforated reflective material designed to put in your attic. It reflects away most of the radiant heat that penetrates the roof, before that radiant heat comes through the upstairs ceiling and into the house.

A white or light-colored roof is also a good idea, as it reflects away lots of solar energy, not just in visible spectra but also ultraviolet and infared.

Best to keep the house from getting too hot in the first place, rather than spending dough to extract the unwanted heat.
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Old 03-27-2008, 05:40 PM   #9 (permalink)
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bhazard -

Quote:
Originally Posted by bhazard View Post
What happens when the foil starts ripping and blowing away in the wind? Foil isnt very strong. Maybe try some sheet metal?

Might as well just have an old tin roof.
In an ideal world (lots of money, no complaining neighbors) I would do that as a "second roof" so that there is an airspace serving as an insulation layer between the roof and the tin roof. This way the main roof would remain shaded and would not have any of the "hot tin roof" parts convecting heat to the house.

Better yet, with even more money, the tin roof would be solar panels generating at least enough electricity to power an AC unit. Shade and AC all in one!!!!

WaxyChicken, how windy does it get where you are?

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Old 03-27-2008, 05:46 PM   #10 (permalink)
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WaxyChicken -

Quote:
Originally Posted by WaxyChicken View Post
Planting for shade:
In this part of Arizona it takes a lot of time and money to get trees to a good height.
There's money for buying, time for planing, money and time to water enough to grow a good size tree in the desert.

Shade Screen:
A Shade screen wouldn't get the roof and the expense would be much higher than just simply buying aluminum foil and using my staple gun to shingle them on the roof.

what about the ''Oven Effect" though?
I wouldn't want a tin roof in direct contact with the house. The metal will heat up and convect into the building. The good part would be that it would cool very fast at night and radiate to the "infinitely cold" night sky.

Assuming your roof is a "normal" shingle color, I would beg the wife for permission to paint the roof white with some kind of elastomeric paint (i.e. something like this : http://www.elastek.com/home.html). A white roof is the only way to go in the desert (aesthetics be damned).

CarloSW2

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