NEW building codes for lighting, air-conditioning and lifts could be unveiled by the end of the year in an attempt to make buildings more energy efficient. Energy wasted by leaving on air-conditioners, lights and lifts in commercial blocks when no one is there is believed to cost at least $5 billion a year. A code for buildings was being drafted and officials hoped to consult affected parties at the end of the year, said the Principal Assistant Secretary for Planning, Environment and Lands, Mary Chow Shuk-ching. The code could specify individual controls for lighting fixtures and air-conditioners or specify the wattage for lights, but Miss Chow said the details were still being worked out. Miss Chow said the code could be applied retrospectively because most of these measures were easy to fit into existing buildings, unlike new building ''envelope'' standards which will be introduced under an amendment bill to the Buildings Ordinance gazetted yesterday. The bill will be introduced to the Legislative Council on April 20 and it is hoped the regulations will be ready by October. Bidders for work on the sewage disposal strategy were invited to participate in a pre-qualifying exercise yesterday, even though the strategy is under review. The work is for the design, construction and commissioning of sludge treatment facilities at Stonecutters Island. The Assistant Director for Environmental Protection, Mike Stokoe, said the sludge facilities would be needed regardless of the outcome of the review and it therefore was not jumping the gun to start pre-qualifying people.