Bay windows are a common feature in newer flats, even though their benefits are questionable, because developers love them. But the days of a 30-year-old government policy that makes the windows highly profitable for developers may be numbered. Bay windows are thought to save energy by helping light up a room, so they are exempted from a site's gross floor area. The developer pays nothing for the space they occupy but can charge a homebuyer thousands of dollars per square foot for that space. Secretary for Development Carrie Lam Cheng Yuet-ngor told the Legislative Council's development affairs panel yesterday that the government welcomed a recent suggestion that the exemption for bay windows should be reviewed. To qualify for the exemption, a bay window should project not more than 50cm from the face of the external wall; its base must be more than 50cm above the floor of the room; and its top must be at least 50cm below the ceiling. Developers have been building ever larger bay windows that can take up as much as 20 to 40 per cent of the space in a bedroom, according to a recent report by Radio Television Hong Kong. It is easy to find a bedroom in new developments that is not large enough to accommodate a bed unless its foot is placed within the bay window. The Council for Sustainable Development recommended in a report last month that bay windows should not benefit from the exemption, since they did not enhance the living environment. Singapore has already removed bay windows from its land cost exemption policy, as they had been found not to be useful but instead increased the temperature in rooms, requiring more energy to cool them down. Barry Cheung Chun-yuen, chairman of the Urban Renewal Authority, agreed last week there should be a cap on the size of bay windows so they do not take up too much space in a bedroom.