Monday, July 29, 2013

A Highly Reflective White Roof Coating for Home Cooling

I've received reports from two people now who have applied a coating of reflective white hydrated lime to their roofs in order to  lower attic and living space temperatures and reduce cooling costs.

While you might expect the lime to wash off in the first rain, it does not, and appears to last for several years.  It is cheap, readily available, and easy to apply.  

According to David and Wolfgang it is quite effective in reducing attic temperatures and AC bills.

David's Experiment
David reported on his white roof experiment back in 2010.  

On performance, David reports:
- House temperature with AC off 87F to 92F before, and 79F to 82F after coating.
- Attic temperatures before 120F to 140F, and 90F to 97F after coating.

This has resulted in much less AC run time.

All the details on David's white roof coating...

Wolfgang's White Roof
Wolfgang after looking at a number of potential coatings for his roof decided to give the hydrated lime a try.  
The house is located in Texas.

Reflective hydrated lime roof coating

Wolfgang's records indicate:
- Average summer day saving of 10 KWH per day
- Attic temperatures drop from as high as 150F to just a few degrees above ambient
- Estimated drop in AC runtime of 40%
- Payback period of 60 day

All the details on Wolfgang's white roof coating...

If the hydrated lime is not appealing, there are commercial white coatings available that can be applied.  I'd like to hear from anyone has tried one of the commercial coatings.



  1. Any update on how David's coating has held up over time?

    1. Its on David's page:


  2. I'll see if I can get David to leave a comment here on that.


  3. David apparently had his roof replaced after two years as it was old. He told me, though, the lime was still up and ok and would have lasted even longer. Maybe David can chime in! Wolfgang

  4. Many people have emailed me about their interest in "hydrated-lime-painting" their roof over the past few years. Most everyone wants to know how it holds up over the years. I kept the coating on my old roof for two years. I would have kept it on there longer, however, my roof needed replacing and secondly my wife did not like the color. We never got any complaints from neighbors or inspectors but did get a few puzzled looks. One winter when it snowed, I said to my wife, "LOOK honey... everyone's roof is white now! Isn't it BEAUTIFUL!!!" but she was not convinced so, in the end I went back to the standard brown shingles to make her happy. However, I installed some sheets of Styrofoam INSIDE my attic on the upper rafters. With my new ridge vent going all the way across the roof's peak, the Styrofoam has an airgap above it that allows most of the heat to go up and out. This system is INVISIBLE from outside the house. However, this Styrofoam method is NOT as effective as the white hydrated lime paint on top of the roof. My attic temperatures go up to about 115F rather that the 100F I got with the hydrated lime method. So it is a compromise between cooling the attic down... and cooling the wife down. To answer the question about how well the painted roof will hold up? ... I didn't see much if any loss during the 2 year test. I put the stuff on THICK because it is really cheap. Most people, I believe are put-off by the NAME. It is also known as WHITE-WASH. This makes us think it will wash-off. Of course it will... but so does every other paint eventually. This stuff holds pretty darn good as long as it gets a chance to dry...which only takes a couple hours. Basically you don't want it to RAIN too soon after applying it. After half a day of drying, you are OK. By the way, I have always been happy to answer all the emails that come my way. Thanks to Wolfgang for his efforts and data gathering on his home. Someday, this roof coating will be much more common I hope.

    David M. Mundy

  5. David thanks for the update. Maybe Gary will add this to your page on his site.

  6. I put hydrated lime on my roof. I live in Alabama. I did have an issue with it not allowing the shingles to wick as they are suppose to. I did put it on thick, so My advice is to put it on thin and even, do not put enough on to stick the shingles to one another.

  7. There are two types of reflective roof coatings to choose from: white elastomeric coatings and aluminum coatings. The selection of one of these two types of coatings will be based on the energy savings you are trying to achieve, as well as the material you are looking to coat.

  8. A Highly Reflective White Roof Coating for Home Cooling is the best cooling for home. You have posted that is great information for me. I will come to know to you more detail about this. Thanks a lot mate.a
    roof installation

  9. Nice article.Yes if you are using a white coating its good temperature also goes low when the temperature is higher outside. but i am using white shingles in the roof which is suggested by roofers in birmingham and i realise it really works.

  10. I am going to give this Hydrated Lime Coating a try... My roof still has years of life left iwith it, otherwise I would choose the elastomeric option, this is a product I used extensively as a house painting contractor and its ability to flex is amazing. It does last for years depending on the quality of the application. Specifically any prep involved, cleaning but most important the thickness of the applied product, many folks have no clue that there are specified thicknesses which have been tested to give the rating for how many years it will last. The ONLY way to be sure is to measure the thickness of the application at different times you are spraying, rolling the material. Last year I blew in 1000.00 worth of the cellulose insulation in my attic. It was worth it as in the winter my heating is so minimal its unreal, I use a Williams 70% efficient gas floor model heater rated at 900 sq ft heating. My house is larger I simply keep a lot of doors shut. While the heaters efficiency is low (70%) I got it for free on craigslist, normal retail 800. My monthly gas bill during the coldest winter months is 17 to 18 therms which costs about 20.00. Keep in mind I do use gas also to cook every night and to heat my water heater. I never eat out so I'm always cooking, washing dishes and showering in addition to my heating. The attic insulation was done simply on a whim although I felt a lot of drafts upon moving into this home.. I also removed the siding and used Tyvek House Wrap when replacing all windows. The difference was noticeable as my 1927 house was last wrapped in the 1940's I assume. A noticeable difference either imagined or realistic was noticed by me.
    I removed the central heating and cooling unit from my roof, running it accomplished nothing. Any maintenance attempts to make it work to any measure failed No real air movement occurred through my vents and the unit just ran, you couldn't even hear it either. I now cool with a Master Cool Swamp Cooler rated for a 2400 sq ft house. My house is 1200 sq ft. In the hottest part of the summer there is no need to even turn it on until 2 pm due to the attic insulation. I run a 1 hp motor in the unit with a high output water pump for the pads. It is overkill, but my house is a steady 70 degrees. My water bill increases about 20.00 a month elec 15.00 or so additional. It is louder and provides a lot of replacement air which is good and bad depending on the time of day and my napping patterns.
    Back to the hydrated lime application. I am going to do this as soon as the presumed "El Nino" rainy season is over here in California, I reside in the central valley in Stockton...
    My attic is ventilated on both ends with a vent on each end measuring 12 inch wide X 4 inch high, alone it was minimal. Two additional large turbines were added, I keep them oiled so they turn freely, they have bad points due to the fact a child could remove three screws, crawl into the attic space to access the crawlspace door to enter my home and let in an adult to rob my home. (A very realistic scenario)
    I also have a crawlspace under my house of 1 ft to 2 ft and a few vents for natural air circulation. My interior wood floors which are uninsulated underneath do get a bit colder in the winter. No plans come to mind to fix that issue. Maybe perimeter insulation, maybe.
    I must commend whoever came up with this idea of Lime on shingled roofs in the US of A. The cost is perfect, seems easy enough and efficient for the cost...
    Ideas of this sort that wont ruin any given type of investment ie. our homes are worth the risk in my opinion. As far as what my neighbors have for opinions on the job is irrelevant to me as they all dislike me anyway due to my skin color. Until later in the warmer part of this year (2016) I am SFSurfdude signing off, coming direct to you from the ghetto located in Stockton, Ca.


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