A roof coating made of waste cooking oil from restaurants that can detect temperature changes has been developed in the U.S.

The eco-friendly coating, which is practically odourless, aims to solve the problem of roof designs which either reflect sunlight through their light colours, saving consumers money on air-conditioning but increasing winter heating costs, or "hot" roofs, which are dark and trap heat, saving consumers money on winter heating bills but not in summer.

The roof coating can help cool and heat a house on demand. In tests, it reduced roof temperatures in warm weather from 50 to 80 per cent, according to researchers. In cold weather, the coating raised roof temperatures up to 80 per cent versus traditional roof surfaces.

The coating could be applied to many roof types, according to researchers. It was developed by scientists at United Environment & Energy LLC in Horseheads, N.Y.

"It will help save fuel and electricity and reduce emissions of volatile organic compounds from petroleum-based roofing products," said Ben Wen, the company's vice-president. "In addition, it will provide a new use for millions of gallons of waste oil after it is used to cook french fries and chicken nuggets."

The coating was presented Sunday at the 239th national meeting of the American Chemical Society in San Francisco. Researchers expect it could be available to consumers in three years.