MASSIVE redevelopment is set to take place in Kowloon with the relaxation of building limits. Mongkok, Shamshuipo, Hunghom, Ma Tau Kok and Kowloon City are part of a huge parcel of residential areas in the peninsula which are now allowed higher plot ratios under the new system that comes into effect today. Restrictions, imposed because of the proximity of Kai Tak airport and the sharp turning approach from the west, have been relaxed on 79 per cent of the whole of Kowloon side. The Government estimates about 45 per cent of old buildings completed before 1967 will be redeveloped by 2006. Real estate agents expect flat prices to skyrocket as developers make use of permission to build more floor space on the previous and accumulated sites. However, some of the potential under the relaxation cannot be realised until the new airport at Chek Lap Kok opens since height restrictions will still be applied near Kai Tak. Director of Planning, Peter Pun Kwok-shing, said they hoped the plot ratio changes would stimulate redevelopment in Kowloon. To alleviate the traffic congestion caused by on-street loading or unloading activities and illegal parking in high density domestic areas in Kowloon, the Government has introduced a two-tier plot ratio system for residential sites. The maximum ratio for domestic buildings on sites smaller than 400 square metres or those without adequate parking spaces is 7.5. Depending on the original ratios, this change means an extra 15 to 67 per cent of floor space can be generated for most sites. About a tenth can double the floor area. A higher ratio of nine is given to sites larger than 400 square metres and with provision of car parks. If all the areas given higher ratios were to be redeveloped, there would be 21.05 million square metres of floor space, an increase of about 30 per cent. To assist redevelopment, the Government has to spend $60 billion by 2006 in resuming land to provide recreational facilities for Kowloon residents, according to consultants. The Government estimates the population in Kowloon to drop by four per cent to 1.8 million by 2011. The biggest decrease will be in West Kowloon which is currently the most densely populated. President of the Society of Hong Kong Real Estate Agents, Michael Choi Ngai-min, advised owners to have professional valuers assess the potential value of flats before selling them to developers. ''Under the new limit, the same piece of land may become more valuable and so will the flats on them. I believe many owners will soon be approached and asked to sell their flats,'' he said. However, Mr Choi said property price would not be affected in the short or medium term since it would take a few years for buildings to be completed. Mr Pun said most buildings in the urban area had many owners and it would not be easy for developers to get development rights quickly. Some low density residential areas in Central Kowloon and Kowloon Tong are subject to special control and will not benefit from the new system. Due to the capacity constraints of the transport system, Mr Pun said there was no scope for relaxing the restrictions for these sites in Kowloon Tong, Yau Yat Tsuen and Ho Man Tin. Sites with a mixture of residential and commercial sites will be re-zoned to separate the two kinds of land use to provide certainty in the prediction of infrastructural and transport demands. Under the plot ratio changes, 89 per cent of industrial sites such as those in Kwun Tong, Kowloon Bay and Cheung Sha Wan have increased to a ratio of 12. However, nearly 70 per cent of office sites have had their ratios cut to 12. ''The office sites subject to lowered plot ratios are mainly located in Tsim Sha Tsui and along the Nathan Road corridor,'' Mr Pun said. ''The restriction on commercial plot ratio is required to ensure that the operation of the Mass Transit Railway would be within its capacity limits.'' United Democrat Legislator Albert Chan Wai-yip said he wondered if there was a need to increase the total industrial land available by 20 per cent as most major plants were moving northward into China. Legislator Alfred Tso Shiu-wai, who represented the Regional Council, questioned if the Government should zone land along Nathan Road as commercial. He suggested the Government should leave the choice to developers.