KARACHI: White is the greenest colour. Painting roofs, walls and pavements white or light-coloured is the cheapest and one of the most effective strategies to reduce energy consumption, make homes and offices more comfortable and mitigate the ‘urban heat island effect’ caused by the concentration of concrete structures in cities, said Prof Norbert Lechner at a workshop on Monday.

The US-based expert in energy responsive architectural design with an emphasis on solar responsive design was delivering his lecture, which was part of the two-day workshop held at the NED University of Engineering and Technology.

The workshop, titled Capacity building in research, education and practice for high-performance energy efficient buildings and homes, is organised by the Construction Engineering and Management Group (CEMG) at the NED varsity and jointly funded by the USAID and Higher Education Commission (HEC) under the Pakistan-US Science and Technology Corporation Programme.

Prof Lechner said: “You can experiment it on two apartments located at the same place; paint the roof and walls of one white and the other in a dark colour. This will provide you with the evidence that white makes a big difference in reducing heat gain.

“One can also use shaded windows and create green spaces, for instance vegetated roofs and walls, if one has the means to maintain them.”

He was asked about low-cost options available to Karachiites to prepare themselves for a repeat episode of the severe heatwave that struck the city last year.

An additional effect of white colour was that it reflected radiation back into space, he said.

Tree plantation, according to him, is an effective strategy to lower temperatures in cities but they take a long time to grow.

“This is my first visit to Pakistan which will be followed up by more. The purpose is to share knowledge as well as learn about the building structures here so I can give some recommendations,” he explained.

Building orientation

Earlier, giving a presentation on climate change and the role of buildings and an overview of low energy design strategies, Prof Lechner, who has been associated with the College of Architecture, Design, Construction of Auburn University for 33 years, said that there were still denials against climate change even in the US though concrete evidences existed showing that global weather conditions were changing fast.

“The year 2015 has been described as the warmest year since modern record-keeping began in 1880. The rate of melting ice in Antarctica and Arctic regions is alarming to an extent that you can’t make predictions,” he said.

He also talked about the huge amounts of methane hydrants, which were stored in a frozen form in the sea floor across the world and rising sea level. Climate change, he told the audience, could destabilise these methane hydrants reserves, which in turn could speed up the process of climate change.

Emphasising the urgency to act, he said that worse could happen if no efforts were made to combat the situation that he said had been created mainly due to significant increase in population and desire of more and more people to get affluent and use technology.

According to him, in most countries, buildings have been found to consume more than 50pc of all generated energy to heat, cool and light them. If this energy can be saved, it will not only reduce pressure on the grid, lead to reduction in climate change impact, but will also increase occupant comfort.

“Many of the significant techniques for reducing energy consumption are low cost and some even free. In that context, building orientation [the way a building is situated on a site and the positioning of its windows, roof-lines and other features] is the single most important factor,” he said.

The ideal strategy, he said, was to have controlled sunlight that could be achieved with the help of extended roofs, window blinds, roller shades, fixed overhangs and traditional shutters with louvers.

“Shading should be on the outside as it reduces heat gain up to 80pc. Windows on the east and west facades do not have to face east and west [as doing so will expose the house to sun till evening]. A well-designed building will harvest the winter sun and reject the summer sun and collect daylight all the year round,” he said.

A radiant barrier, a thin sheet usually made of plastic or paper with polished metal surface that reflected 95pc sunlight or any other light, was also an important tool to combat hot weather conditions, he said.

The barrier is usually placed underneath the roofs facing towards the sun with an air space of one to two inches between the roof surface and the sheet.

A correctly oriented building, he said, helped reduce 50pc consumption of energy used in heating, cooling and lighting.

Prof Lechner, who himself is an inventor of different types of heliodons (a sun emulator tool), also explained the principles for achieving solar access and shading all the year round with the help of his equipment.

He also highlighted the need for using solar water heathers in order to reduce energy consumption.

Published in Dawn, April 5th, 2016