There has been controversy over the "wall effect" (, literally "
folding screen building") caused by uniform high-rise developments that adversely impact air circulation, leading to an aggravation of the
urban heat effect while also impacting public hygiene and contributing to air pollution. In 2006, the environmental group Green Sense has expressed concern that their survey on 155 housing estates found 104 have a "wall-like' design". It cited estates in
Tai Kok Tsui and
Tseung Kwan O as the "best examples". Then-head of the
planning department, Ava Ng, argued that the air ventilation factor had been taken into consideration with regard to the auction of all prime sites on the land application list, and mentioned that the erection of tall buildings at these sites would not create any "wall effect". In May 2007, citing concern over developments in
West Kowloon, and near
Tai Wai and
Yuen Long railway stations,
Wong Kwok-hing, of the
Hong Kong Federation of Trade Unions, put forward a motion calling for measures to reduce screen-like buildings that maximise good views at the expense of air flow in densely populated areas. The motion was vetoed by
functional constituency representatives. ==Lists of estates==