White Painted Roofs on Buildings and Residential Homes Cool the Home and the City, and Provide Savings on Summer Cooling and Winter Heating Costs.
White Roofs May Even Help Mitigate the Effects of Global Warming
Several years ago I got up onto the roof of the residence where I lived, and painted (well, top-coated really) the roof with a thick bright white tar sealant.
The summer was beastly hot. For the most part I was not home during the hottest part of the afternoon but this particular summer, I was. I had broken my arm in a work-related incident and was off work for the next two months. Normally, I would be leaving for work around 2:30 or 3:00PM and my residence was still in partial shade at this time of the afternoon.
Some rather fortunate positioning gave me shade trees from about noon until 3-PM. Mornings from 9 A.M. ‘til noon, and from 3PM until after 6:30PM I had direct sunshine on my roof and my home became unbearably hot inside.
Even with the windows open and all the curtains closed (these where heavy but light-colored curtains too) and fans running, the ambient temperature inside the home typically would reach the upper 90s Fahrenheit. It was hotter inside than outside! The flat black tar roof was the culprit.
Being confined at home with a cast on my broken arm I was discovering how hot my place really was! I mean it was BAD, folks! I had all the windows open, fans blowing the hot air out to virtually no avail. In desperation to escape the heat and this is no lie, I set my television up on a table in front of an open screened window that faced my back yard and I sat outside, in the back yard, watching TV like a bizarre drive-in movie theater!
It was unbearably hot inside and the temperature would not fall to comfortable levels until 8 or 9-PM at least. I could endure this strange home entertainment arrangement for a day or so but really, something seriously had to be done. The blazing summer heat was making my home unlivable for some 3 or 4+ hours every afternoon that late July and August.
Bright White Roof Sealant for the Home
I bought a 4-gallon can of a snow-white roof-tar sealant. It fills cracks and seams, and protects against leaks. Unlike ‘reflective’ roof tar which has an aluminum component in it that upon being applied to the roof, would float to the surface and provide some reflectivity, this product was true white.
I got up on the roof with a paint roller on an extensible handle (and yes, with a cast upon my arm folks) and my 4-gallon can of white rubber-tar sealant and I painted my roof. The 4 gallons was just barely enough. I could have used one more gallon for a thicker coating towards the end, but I was able to stretch it out to complete the job. The results however, were amazing!
The very next day, the home was about 10 degrees cooler inside. The outside temperature was about the same as the previous day, but the inside ambient temperature was in the low 80s with the same windows open and the same fans running. That was a full 10 degrees Fahrenheit cooler inside my residence!
That winter I did not notice if it required more energy to heat the home due to lacking the black tar roof and radiant sunshine's warming effect. In fact, I suspected that it took less energy to maintain room temperature as the rubber tar itself is an insulation material despite its bright white reflectivity. The home was comfortably warm and I don't recall having paid more for energy costs that winter for it.
Urban Island Heat Effect and the City
I was just reading on MSN an article about painting roofs white in the city to reduce the ‘urban heat island effect’ and some studies show that if every building in an urban city were painted white, the temperature of the city itself could drop by as much as 1.1 degrees Centigrade (2 degrees Fahrenheit.) For anyone living in the big city they already know that ‘urban heat island effect’ does make the city hotter. Those hot days cause air conditioners to be used more and at higher settings, often to near brown-out results.
Here in Toronto, Canada we experience that every summer. Toronto is a large city with a population of over 4 million people. I even installed a innovative balcony tarpaulin sunscreen/awning to help mitigate the summer sun's heat.
The MSN.com article goes on to state a negative side effect of white roofs though. The cooling effect in summer is good but the white roof alledgely causes homes to be cooler in winter and thus, increases the need for heating. I might disagree.
If there is more insulation in the roof not only is heat loss through the roof negligible, the revese is also true. Radiant sunshine warmth should not be getting through the insulated roof from the outside. Ignoring for the moment the increased weight a snow-covered roof must bear, a roof with a blanket of snow on it has an insulation effect too. The white roof would not warm as fast or as much as a dark or black roof does in winter, and the snow would not melt and slide off.
That would be the main concern; the weight of the snow that a now white roof might now accumulate. It the roof is steep enough, it will slide off anyway no matter what color the roof is. This pertains more flat roofs, typical for city buildings.
My experience is this: the cost of the 4-gallon bucket of bright white roof sealant (cost: under $50.00) probably saved me that much in cooling costs in the first summer alone. The immediate effect of a cooler ambient temperature alone was worth the cost of the material used and I truly doubt if my heating costs that winter went up proportionalty as a result.