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Paint roofs white and cool the earth

September 14, 2008

WATER WISE

Your roof colour matters

S. VISHWANATH

California already mandates a white roof for its buildings but if it makes energy sense and economic sense, white insulating and reflective roofs should become a matter of choice rather than being imposed through legislation.

— Photo: M. Moorthy

Practical: Coating on ceiling reduces heat inside a building.

If you ask Hashem Akbari the one thing that he would do to save the planet from the ill-effects of global warming, he would say paint the roofs of the homes of 100 of the world’s largest cities white and change the road surface to a light colour. Who is Hashem Akbari? He is a physicist and part of the heat island group at Ernesto Orlando Lawrence Berkeley National Laboratory and was presenting a paper at the fifth annual climate change conference in Sacramento, California, on September 9, 2008. (His website is at http://heatisland.lbl.gov/ for those who need more info).

White reflective roofs

It is well known that roofs are the largest heat gainers in buildings and also that if the roofs are painted white they would reflect a large percentage of the incident solar radiation, especially the infra red radiation, away and keep the building cooler. A good reflective white paint brand like the Australian paint called Insultec, claims to reradiate 95 per cent of the infra red rays and 85 per cent of the ultra violet rays, thus reducing the heat load inside the building by 30 per cent. This can reduce air-conditioning costs considerably in buildings. These insulating paints also have the advantage of being water proof and prevent the conduction of heat also.

They can normally be applied on any surface including RCC roof surface, tiles, asbestos sheets and even on poly-coated sheets. Costs are supposed to range from Rs. 40 to Rs. 50 a square foot .

While at an individual building level there is a saving in electricity consumption and having a cooler building, Hashem Akbari adds it up by arguing that lower power consumption means lesser requirement from power plants and therefore lesser generation of CO2 and NOx by the power plants, therefore contributing to the lessening of global warming. Each building can therefore contribute in its own way to lesser emissions from power plants.

Cut in emissions

A 1000 sq. ft. of roof area, a typical roof on an average 30 x 40 site in Bengaluru, painted white can offset 10 metric tonnes of carbon dioxide emissions as compared to a dark roof, say with tiles.

Consider this: 44 metric gigatons of carbon dioxide and other green house gases would be offset if the world’s 100 largest cities converted their roofs to white and made their roads lighter.

California already mandates a white roof for its buildings but if it makes energy sense and economic sense white insulating and reflective roofs should become a matter of choice rather than being imposed through legislation. Asphalted and tarred roads are dark in colour and absorb heat as any two-wheel driver will tell you during summer time. Roads which are dark and blacktopped can also be changed to lighter coloured and more reflective concrete roads.

Since roads make up 25 to 35 per cent of a layout or a city, changing their colour to lighter shades and increasing their reflectivity will cool the immediate surroundings by 2 to 3 degrees Celsius and also contribute to power savings. The importance of avenue plantations and tree shading on both roads and buildings cannot be re-emphasised.

Not only does it contribute to the micro-environment and biodiversity but there is increasing evidence that on a larger scale this can reduce global warming.

Good reflective and insulating paints on the roofs also have another advantage on roof and water. They can be cleaned easily. Their runoff coefficient — the amount of rain that runoff during rains — is higher; therefore, more rainwater can be harvested from such roofs. When the paints are made of inert material and are non-toxic the run-off water quality is also improved and this rainwater can be harvested and even used for drinking.

Thinking smart about roofs helps the building, the earth and water. The roof above your head not only protects the individuals inside but can contribute to solve problems related to water, energy and global warming.

In a city, smart roofs are the path to water wisdom.

www.rainwaterclub.org

www.arghyam.org

zenrainman@gmail.com

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14 comments

  1. Very interesting article. Is there data on how white roofs compare to, say, rooftop gardens, which can both absorb heat and offset carbon dioxide emissions?


  2. it is good job


  3. a quick explanation of why white paint works to cool the planet

    1 around 50 percent of sunlight is visible light

    2 around 50 percent of sunlight is heat

    3 visible light is a frequency of light NOT absorbed by the atmosphere

    4 some HEAT (infra red) from the sun IS absorbed by the atmosphere directly (greenhouse gasses which makes the atmosphere warmer).

    5 HEAT from the sun also warms the surface of the planet and this HEAT is then radiated back into the atmosphere again being absorbed by greenhouse gasses.

    6 visible light is poorly absorbed by the atmosphere, some of it gets reflected back by the atmosphere.

    7 the visible light that doesn’t get reflected back by the atmosphere is either reflected by the surface (eg a snow field) or absorbed by the surface (an asphalt carpark/ road). this absorbed light heats the dark surface. this heat is then radiated into the atmosphere and is absorbed by greenhouses gasses makiig the atmosphere warmer.

    8 by painting your roof white and other surface you reflect around 50 percent of the visible energy from the sun, a significant amount of this is reflected back into space WITHOUT heating the atmosphere.

    9 by painting enough roofs you make buildings cooler and cool the atmosphere. air conditioning works easier to cool houses because they are cooler, perhaps you wouldn’t even need air conditioning?

    if you are thinking of using white paint to cool your roof you will need a special white insulative paint that both reflects the visible frequencies of light and stops infra red frequencies from heating your roof.


  4. Thanks for the detailed explanation wookiemesiter appreciated.


  5. I am interested in getting our rooftop painted white. Iam a resident of noida, near Delhi and summer is harrowing. WHich paint would be best suited? I mean the contents? oilbased or what?


  6. Try INSULTEC a paint from Australia but now made in India too.


    • Please name the brand of paint(s) equivalent to INSULTEC manufactured/marketed in India (Delhi) (if different)? Thanks.


  7. […] Today found this great post, here is a quick excerpt : heat reflective roofs should become a matter of choice rather than being imposed through legislation.This can reduce air-conditioning costs considerably in buildings.


  8. Very interesting & useful. Can any one indicate the range of reflective paints available and dealers at Chennai?


  9. Painting the roof is one of my favorite hobbies


  10. Knowledge and Good idea to. Dealing with Heating and air conditioning


  11. My husband is planning on repainting our house, roof included with paints he bought at add4green. He bought various kinds of paint. He said that some of those are insulative and reflective and will reduce our heating and cooling cost. Hope it works because anything to reduce our expenses is good.


  12. Outstanding publish. I was examining consistently this kind of site using this program . inspired! Very helpful information precisely the remaining section 🙂 I personally take care of similarly info a lot. I was in search of this specific specified facts to get a incredibly lengthy moment. Thank you and best of chance.


  13. we painted the roof of our apartment building with Insultec several years ago, and it certainly has reduced the heat in our flat [we live on the top floor].



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