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Has anyone done any research into "cool roofing" for their houses? Answered

Like white colored material to raise solar reflectance? How much energy can be saved in an avg. sized house? I live in FL and I'm faced with a re-roofing project pretty soon...



9 years ago

I painted my (slanted tar-shingle) roof white using HYDRATED LIME mixed with water. It dries a BRILLIANT WHITE. and it is very cheap to buy. (only about 7 dollars for a 50 pound bag!) My attic was 145 degrees F. Now attic only gets about 100 degrees hot !! I have done many other experiments: for example installing 2 roof turbines.... results... attic went from about 145 degrees to about 139 degrees. (so... not much effect).. So-far this (lime-paint-roof) is the cheapest easiest and most effective method i have found to reduce attic temperatures. However, the wife doesnt like the "looks" of the new roof. I wouldn't do this to a GOOD ROOF. My roof is needing replacement this summer anyway so i did it as an experiment. I used 2 bags total 100 pounds of hydrated lime powder to paint my roof. Total cost about $14.00. and about 5 hours of work. I am not certain how well the dried lime will stay on the roof during rainstorms. Only have 2 days of data and no rainstorm yet. Anyone doing things like this to your house may i suggest you get a wired-thermometer so you can monitor your attic temperatures for BEFORE and AFTER to see what the effects are. Many digital thermometers have a HIGH and LOW memory. I note the reading each day, then clear the thermometers memory to wait for the NEXT days high and low. When mixing lime with water use a lot of lime. Don't breathe the dust. Wash off any lime you get on your skin (it kinda burns). Lime-water "paint" goes on kinda dingey looking. Looks almost GREY. But it dries BRILLIANT WHITE like it snowed on your roof. Another product called "elastomeric reflective roof coating" will reflect heat also. It comes in 5 gallon buckets, but problem is you will need at least TEN BUCKETS to do a 1000 square foot house roof. and each bucket costs about 60 bucks. Thats a cost of 600 dolllars!!!! So i am pretty excited about the hydrated lime method, only costing 12 bucks. I found somewhere on internet that they suggest only using HYDRATED lime, not the other kind (organic lime??) for this purpose.


10 years ago

Actually, there is a silvery material used as a roof covering on commercial buildings, and it's silvery color is specifically for the affect that you desire. I'm sorry that I don't know it's name. My experience is tertiary...An old friend purchased a small factory building several years ago to convert it to Artist's lofts and its roof is covered by the material...I believe it's a rubber-like membrane, about a 1/4" thick silver on one side, unknown inside or on the other. As far as I know, it IS susceptible to mechanical damage...or said in plain English, it's not suitable for installations in which trees overhang, since falling branches will quite easily puncture it. When we would go up there (for the occasional midnight beer, when we were gutting and refitting the building, we were repeatedly warned to a) keep to a very specific path, and B) we were not allowed to walk in heavy boots...Might have been overkill, but I also recall that he had to patch an area where one of my pals didn't follow the rules...He was, to say the least, kinda pissed off. I also saw a program several years ago on This old House, done in NM, in whcih they spray coated the roof of an adobe house with about 3 or 4 inches of some insulating foam, then coated it with a highly reflective paint. So, yeah, I think there are solutions, but being a native of Northern Ohio, and being shaded by a pair of 100ft tall Nut trees ( White Oak and a Pignut Hickory), one literally on each side of the house, I'm more concerned with keeping it in rather than keeping it out.


10 years ago

There are many materials which you can use to increase the thermal resistance to your roof, painting your roof white is one of them.
Most roofs that have some kind of treatment (painted white, growing medium) are flat roofs (designed with a slope of less than 15% but more that 2%). Sloped roof homes typically use higher R value insulation to achieve the same results.

Depending on the type of roof you have there are a few options, and if you are planning a re-roofing job sometime in the future there are many doors which are open to you. If you have a flat roof you can explore the option of having a white topping which will increase the reflectivity and cool your house. If your structure can handle it a better (and more awesome) option is to have a shallow growing medium, 6" is plenty. You won't be able to use the roof as a yard or anything but it would dramatically decrease your heat gain. Also, if you choose the right grass you won't need to go up there and mow it either.

How much energy can be saved in an avg. sized house?
That is really a function of how much your hydro costs, and how much you use. Depending on where you are located the savings can vary, a typical house can see a yearly savings of anywhere from $400-$1000. Over a typical lifespan of a roof (say 50 years) that's a fair chunk of change. There's an argument to be made regarding the savings and if it offsets the cost of installation (as growing mediums and specialized roofs can be costly), however if you think beyond numbers you are reducing your carbon footprint and helping good ol' Mother Earth.

A few things to consider, I hope this helps!