Paint roofs white and cool the earth

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.

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Ecological Architecture in India

House calls
Nirmala Ravindran
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–> DOWN TO EARTH: CHITRA VISHWANATH Far from the madding crowd would be an understatement to describe the location of architect Chitra Vishwanath’s home.“At that time, this was the cheapest plot of land we could find,” she says of the 1,500 sq ft plot. Set amid bamboo trees and greenery, the house in Vidyaranyapura cost the Vishwanaths Rs 4 lakh to build, 13 years ago. With a 1,000 sq feet garden, the house stands as a testimony to Chitra’s pioneering work in using earthfriendly construction material. Her husband Vishwanath is a civil engineer and one of the pioneers for the move to create compulsory water-harvesting in Bangalore city. “We had to realise that bricks and sand and marble cannot be carted around the country. We had to find ways of using local material that conserve and save energy.” Chitra Vishwanath�s eco-friendly philosophy is intertwined with her home and lifestyle Her home, Chitra admits, was a laboratory of sorts. “There are things you can’t try in a client’s house, but did with ours.We still find things to add,” she says.The house has been built with soil bricks that have not been plastered or painted, terracottacoloured floor tiles and numerous skylights. It has various levels with the mezzanine floor overlooking the main seating area. And there’s a big surprise: there are no ACs or ceiling fans anywhere in the house. “We’ve never used them; the house never gets hotter than 22° C even in summer,” says Chitra. The couple’s eco-friendly philosophy is intertwined with their home and lifestyle. There is a compost pit to handle garbage and water recycling on the terrace. “We even have a toilet upstairs that separates solid and liquid matter,” says Chitra. There are solar cookers on the terrace cooking the afternoon meal of rice and dal, while rice is being grown on the other side of the terrace. The architect uses her house to present her case to apprehensive clients. “Most people are scared of eco-friendly material because they think it’s high maintenance. But once I’ve show them my house, they usually succumb,” she says. “We want to be able to utilise this land for everything we need: water harvesting, light, ventilation and energy. We’ve grown so many trees around the house that even if the neighbour decides to build a high-rise, it won’t affect anything here,” she adds. For this couple, eco-friendly is not a fashion statement but a way of life.

Urban floods in Bengaluru

The problem is in the planning

Water, water everywhere…planners, institutions and individuals can take several steps to mitigate the physical and economic impact of urban flooding, says S. VISHWANATH

— Photo: K. Murali Kumar

The deluge: The state of affairs in an upmarket villa after a lake breached on the Whitefield-Hoskote Road.

A series of flooding events across Bengaluru has brought into sharp focus the need for better management of rain. Though nothing on the scale of the Kosi floods yet, it has caused severe economic and physical damage to the city and left many psychologically scarred. The coming of the rains is looked at with trepidation and newer areas of the city seem to be affected every time it rains.

Several interesting facts emerge around urban floods. In Bengaluru, it is clear that it is rain which causes the floods unlike, say, a city like Patna where rain could cause the Ganga to swell and flood the city. Surprisingly, recent evidence suggests that it rains more in the city and slightly downwind than in the regional rural periphery.

This is according to a study by NASA scientist Marshal Shepherd. The urban heat island effect, where cities are warmer than their surroundings and which causes the build-up of rain clouds on the city; pollution, which allows rain to coalesce around dust and oil particles; and the wind-break effect of cities, which causes the clouds to discharge on the cities, all seem to contribute to this phenomena. Bengaluru needs to prepare for more rain than average and higher intensity rains at the same time.

Cities also increase runoff as more and more soft agricultural and fallow areas get built upon or paved. From a small well-mulched site, hardly 10 per cent of the rain falling will runoff as storm water. However, build a house on the same site and pretty much 90 per cent of the rain falling will runoff as storm water. Buildings increase runoff tremendously in the Bengaluru context and the storm water drains have to cope with this increase.

Waste management

Solid waste management is crucial to flood management since most of the uncollected garbage will end up in the lowest area, usually the storm water drains, choking them and reducing their ability to carry storm water out.

Tanks and lakes which collected surplus water and recharged the groundwater or dissipated it slowly are on the decline. These are built up, like the ISRO headquarters built on an old tank bed. They then become prone to flooding or transfer the flood problem downstream.

The network of tanks and the valleys and drains connecting them are in a bad state of management with encroachments on several of them. With no institutional approach to manage the tanks and the valleys, little is done except during the flood event itself to ensure that the channels flow freely and that the tanks are not encroached upon. Traditional storm water management techniques simply collect the rain water and funnel it across the city downstream. Newer methods combine traditional approaches with new ones such as Sustainable Drainage Systems (SUDS). It employs a range of natural processes to purify urban runoff. Removal of sediment, bio-filtration, biodegradation and water uptake by plants all help to remove pollutants. Vulnerability maps of areas prone to flooding need to be prepared for citizens to become aware of the choice they make for where they live.

Rainwater harvesting

Even as the Government is working towards making RWH mandatory in the coming days for the city, the system has one of the best potentials to replenish ground water, improve its quality, provide supplementary water for domestic requirements and mitigate flooding. If every building in Bengaluru can store or recharge 60 mm of rain in a single day it should be possible to mitigate the effect of almost every flood except the rare. This means that a 100 square metre roof area will need to store or recharge 6,000 litres of water. Zones with the best possible recharge and zones with the best possible storage need to be identified in the city and steps taken to encourage people to go in for rainwater harvesting.

A recharge well of 3 feet diameter and about 20 feet depth can send in up to 12,000 litres of water into the ground in a single day, provided lithological conditions are favourable. The city needs many such recharge wells in the catchment area of critical flood zones to detain flood waters and top up the aquifers instead of surface flow flooding.

At the broader scale, tanks and lakes need to be networked and managed as retention and detention structures. With rainfall prediction accuracy being developed, tanks have to be linked to catchments and kept ready to hold the maximum water to dampen peak storm events. A deslited tank in Bengaluru can recharge up to 11 mm of water every day while an undesilted one can recharge hardly 1 mm. Desilted tanks can recharge aquifers quickly, lower the surface water levels and be in a position to function as flood mitigators. Full tanks are not good at dampening floods.

Flood insurance

In Europe, urban flood research has been driven by insurance companies who want to understand risks associated with floods and plan premiums accordingly. This sector has yet to mature in India but taking flood insurance is a wise step especially if your car has been found floating in the basement after a rain. Good advice comes from ICICI-Lombard on its website on what to do after a flood. It starts by saying that you should not return home till the authorities declare it safe to go back. Then the steps recommended are: turn off electricity and gas, make sure the water and food you consume are safe, stay healthy, call your insurance agent, take photographs and videographs of the damage caused and finally take care of yourself and family. Wise words, indeed, and this is water wisdom when it relates to urban floods.

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