Green Roof System to Take Root in Jerusalem Schools

Jerusalem has decided to follow other cities in the world in adopting the green-roof system to improve the quality of life in the city, reduce pollution and noise and improve buildings' insulation and energy consumption.

The green roof system consists of planting vegetation on top of a building's roof on a layer of soil or a growing medium, over a waterproofing membrane. It has a caulking and drainage system to "catch" rainwater.

Such roofs - either flat or sloping - exist in large cities in Japan, Spain, Canada and Germany.

The few green roofs in Israel have been built mainly to cover parking lots and serve as ordinary gardens.

The Jerusalem municipality said on Tuesday it was planning its first stage of green roofs in four of the city's schools. At a later stage, it would offer incentives to set up green roofs in private homes and would eventually incorporate them into the city's future master plans.

The city decided to introduce the green roof system following a survey of green roofs in the world conducted by scientists and architects. The survey establishes the system's many advantages, such as collecting rainwater, thus preventing flooding during heavy rainfalls. The vegetation on the green roofs can also absorb carbon dioxide, the main gas causing global warming, and significantly modify urban heat island (UHI) effects.

A UHI is a built-up area that is significantly warmer than nearby rural areas due to urban development, which causes heat absorption from asphalt surfaces.

A green roof can improve a structure's insulation and reduce the energy consumption for heating and cooling. Studies show that energy consumption to cool a structure drops by 25 percent on the floor under the green roof. The insulation can reduce noise in the structure by up to eight decibels.

"Green roofs contribute to increasing the variety of animals in the city and improve the city's facade," said deputy Jerusalem Mayor Naomi Tzur, who is in charge of the environment portfolio.

The Israel Energy Forum (IEF), an organization promoting energy efficiency, is trying to advance the practice of painting roofs white as a means of reducing temperature and energy consumption for operating air conditioners. This, in turn, decreases the issue of hothouse gases during the power production.

A study conducted in the United States shows that painting roofs white or other light colors can reduce the temperature on the roof by up to 40 degrees. Painting 10 square meters of roof with light-colored paint lessens annual hothouse gas emissions by one ton.