Author Topic: White Roof - A Smart DIY Idea?  (Read 3097 times)


  • Pencil Stache
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White Roof - A Smart DIY Idea?
« on: July 14, 2015, 01:43:48 PM »
Constantly being frustrated by the Florida heat led me to do some googling on white roofs today. At first I ran across elastomeric roof paint you can buy from like home depot in 5 gal buckets but I instantly ruled that out based solely on it's outrageous price.
Then I ran across this article/paper:

It greatly interested me because I love re-purposing things that aren't meant for a purpose. If hydrated lime was sold as a "roof paint" i'm sure the markup would make it cost $150 a bag but since it is a fertilizer or whatever it is super ridiculously cheap. I see a ROI on this possibly being in the 30-90 days range unless it seriously effects the longevity of the roof. There's not much research out there besides a couple people on that builditsolar website that have done it.

Has anyone considered doing something like this?
Any reason not to try it?
Any scientists wanna warn me about spontaneous explosive reactions between roof and lime?

Note* The guy who did this commented on that article 3 days ago saying the coating is still holding up fine after 2 years


  • Bristles
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Re: White Roof - A Smart DIY Idea?
« Reply #1 on: July 14, 2015, 10:31:55 PM »
This is actually a very old answer to the problem and is referred to in a number of texts from the late 18th century.  Usually it was limewash applied onto slate roofs above attics that were used as sleeping quarters for farm staff in Southern England.

I'm not sure how effective it would be in Florida heat and whether it would stick to your roof would depend on the roofing material.

I use limewash on the (stone) house exterior and it is very cheap to make.  I make limewash from lime putty (pour a bag of lime into a plastic domestic trash bin (wear a mask!), add lots of water and mix it as well as you can. After a few weeks it forms a cheese-like putty under a layer of clear liquid).

But you can make it straight from powdered hydrated lime.  Not all outlets recognise the difference between hydrated lime and hydraulic lime, so make sure you get the right one. Be careful handling it and wear mask, eye protection and gloves.

I add a splash of linseed oil to my limewash to make it stick better and be less likely to rub off on people's clothes.

I've not used it on a roof, but it does stick to slates quite well.  It gradually wears off in the rain, but where it was used in the past, they would have reapplied it most years until a thick reflective layer built up.  This practice would probably also have helped waterproof old roofs and stabilise loose slates, so added benefits for those sleeping in the roof space.  At that time lime and it's products were used widely on farms, so it was a readily accessible material.


  • Walrus Stache
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Re: White Roof - A Smart DIY Idea?
« Reply #2 on: July 14, 2015, 10:54:33 PM »
I wonder if you could just throw some aluminum foil up there!


  • Bristles
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Re: White Roof - A Smart DIY Idea?
« Reply #3 on: July 15, 2015, 09:49:55 AM »
Hydrated lime is still caustic.  I would be very concerned about what it was doing to a roof of anything but tile or slate.


  • Bristles
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Re: White Roof - A Smart DIY Idea?
« Reply #4 on: July 15, 2015, 01:32:46 PM »
pH around 12 so it is indeed caustic, however it has been traditionally applied to timber and helps protect against insect attack. Tends not to adhere to shiny surfaces, but will to oxidised surfaces, like old tin sheds.


  • Handlebar Stache
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Re: White Roof - A Smart DIY Idea?
« Reply #5 on: July 15, 2015, 04:08:43 PM »
A radiant barrier might give you the same benefits without having the eyesore of a patchy white painted roof.
One more advantage is that it would not need maintenance as a painted roof would.


  • 5 O'Clock Shadow
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Re: White Roof - A Smart DIY Idea?
« Reply #6 on: July 16, 2015, 11:19:10 AM »
What type of roof do you have?  I've used the white elastomeric paint on a metal roof that was covered in black rolled roofing and it did a fine job.  If you have shingles I wouldn't use anything that "paints" on.