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Retractable white roof for passive heating /cooling ?? Dual season roofing idea? Answered

Last summer my top floor apartment was over 115 degrees indoors with blinds closed !  In a recent email to my landlord to report a broken mailbox I suggested the possibility of painting the apartment buildings roof white .  In reward for reporting the mailbox he says I could paint the roof but only above my apartment  . Cool . He says that the insulation was not adequate when built . The apartment has also gotten down to 30' in winter so I can only guess how cold it would get in here without the current black roof.
              QUESTION ;  Are there any ideas to help solve both seasonal issues ?   I can't re-insulate because I rent .  I was thinking of a retractable white cover for hot summer days that can be removed in autumn . Or maybe even a white paint that would insulate against cold ??   An original idea was something like Bubble foil but I doubt that would stand up to weather.  Any suggestion would be great .    

6 Replies

framistanBest Answer (author)2010-05-16

I have done EXTENSIVE experiments on this idea.  I placed styrofoam sheets INSIDE the attic roof ... so it is NOT VISIBLE to neighbors.see my results by clicking on this link to fieldlines.com website :


I reduced my ATTIC temperature from about 140 degrees... down to about 110 degrees.  This reduced my HOUSE temperature from about 93 degrees to about 82 degrees (most days).  I wanted to take it a STEP FURTHER... so i did what you suggest... I painted HALF of my roof white. I used a product MADE for this purpose called Henry solar-flex (elastomeric) roof coating. which claims to be highly reflective and will "reflect 85 percent" of the heat and light off of your roof.   Here is the problem with that plan.  

 (1)....    The product costs about 50 dollars per 5 gallons.  and it takes LOTS of 5 gallon cans to cover your roof.  My house is 1000 square feet.  I only did HALF my roof and it used 3 five-gallon containers.  Part of the roof is not covered with enough product... so I would estimate i would need another two 5-gallon containers to finish HALF my roof.  So you should expect to use TEN of the 5-gallon containers at 50 dollars a pop.  Thats a total cost of 500 dollars per 1000 square foot of roof.  My wife stopped me at the 150 dollar mark... and now wants us to replace the roof because it looks a little "tacky" .

(2).... The product states on the label "not for use on SHINGLED roofs".  I called the 800 number... and they said it is because the product MIGHT NOT stick sufficiently to a shingle-roof... and it is made for flat roofs.  But I went ahead and tried it because i wanted to know if it would work to reduce the heat.   I did not think it would take SO MANY cans... so i can't give an answer to how well it worked.  I just think it is NOT THE WAY to go, because of the cost.

If you click on the link to my fieldlines.com article, you will see that I used quarter inch fanfold sheets of styrofoam... and it SOLVED  my house overheating problem. at a total cost of about 2 or 3 hundred dollars... and it is INVISIBLE from the outside of the house.   If i had to do it over, i would use rolls of the REFLECTIVE MYLAR plastic sheets.  available on ebay.  It could likely be done even cheaper than the styrofoam sheets.  And... if it was not totally effective, then you could add the styrofoam sheets later. 

My attic has the styrofoam sheets, and i can-NOT add the mylar plastic because it would have to be ABOVE the styrofoam which is already installed.  I expect my electric bill to be reduced by at least 75 percent this summer.... but we dont turn AC on untill house gets up around 85 degrees.

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BtheBike (author)framistan2010-05-24

 Framistan . All great ideas . I actually have the mylar sheets lining my curtains now.  They hold heat in winter , and reflect it in summer !  

I had a feeling that 'special paint' would be super costly . I figure I could go the cheap route with just white paint 1st , and upgrade if needed.   Fingers crossed that it won't get costly . I (un)fortunately  don't have a wife to keep cost in check =) .

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Re-design (author)2010-05-13

Anything you do is going to be expensive and hard to deal with.  Some one is going to complain and then it'll all have to come down.

I don't know what country you live in but in the US an apartment owner that had apts. that got that hot and cold would be sued and would have to close down of fix them.

I would complain to the authorities before I spend any more of my time or money trying to fix his health hazard.

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donald.gillies (author)Re-design2016-06-25

Not true, I read a story on another website of a man whose roof was wearing out, so as an experiment he painted it with $14 of lime. TOTAL COST. It cut the temperature of his attics from 140 degrees to 110 degrees and drastically reduced his air conditioning bill. He kept it for 2 years until the roof had to be replaced. http://www.builditsolar.com/Projects/Cooling/White...

We have flat roofs and I am going to try some plastic ground sheets.

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steveastrouk (author)2010-05-14

You can get remarkable cooling from direct sun with a "second roof " spaced off the first. I'd get a big Tarpaulin and some Grip-Clips and make a tensioned "roof",spaced off by carrying the tarp on the top of paint cans or empty spackle tubs, weighted with a bit of water.

Grip clips are a fantastically versatile way of holding sheets together, I really recommend them.


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lemonie (author)2010-05-13

Can you (proofed-from-water) bag-up some e.g. shredded-paper & a few rocks? (as insulation)


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