NEW offices and hotels will have to be energy efficient under proposals announced yesterday by the Buildings Department. But the department will be unable to say how much energy will be saved for two years. The data will not be available until architects and engineers feed the results from newly-completed developments into a computer database. Assistant Director of Buildings (Legal and Management), Cheng Wei-dart, said the information would be used to assess whether the regulations went far enough. 'We may have to change the targets if we find there is only a minor effect on energy consumption,' he said. The laws, which will come into effect on July 21, follow more than three years of studies by government and independent building engineers. Architects will have to submit building plans showing details of energy efficient measures and how they comply with the new laws. Those that do not meet the criteria will be rejected by the department, said Mr Cheng. Assistant Director of Buildings (Structural Engineering), Ng Hon-keung, said Hong Kong had been forced to catch up with the rest of the world in terms of energy efficiency. He believed many architects tried to include energy efficient features in their buildings, but without a legal framework it was difficult to know. 'The new airport terminal building is the only one we know for sure will be energy efficient,' he said. The rules limit the amount of solar heat that can be transferred through the facade to the inside. This reduces the level of air-conditioning required and will slash power consumption, it is hoped. The maximum level is 35 watts per square metre for walls and 80 watts per square metre at podium level. Mr Cheng said the rules could change the look of buildings, so instead of hectares of heat absorbing glass, designers could use concrete or other materials. But he doubted whether it would increase construction costs. The rules may also boost the development of so-called intelligent buildings where all environmental controls including lighting and ventilation operate automatically. These include external and internal blinds and sun-shades which respond automatically to light and heat. The regulations have been welcomed by engineers who said a lot of energy was being wasted. 'Buildings in the territory are all very, very inefficient in terms of electricity use. The new rules should reduce the operational cost of buildings,' said consulting engineer, Mouchel Asia director, Nigel Mattravers. But one of the disadvantages of the new rules would be to make buildings look dirtier. 'One of the reasons why glass is used so extensively in Hong Kong is that it is easy to clean and maintain,' he said.