PICKY customers are partly responsible for the stratospheric cost of Hong Kong's property, according to a local housing expert. Dr Richard Wong Yue-chim said the desire of tenants and owners to move upmarket was an important factor in the cost of housing. ''Many people are just not happy with the unit they have or with just one unit,'' said Dr Wong, director of Hong Kong University's Centre of Economic Research. Dr Wong is preparing a study sponsored by the Real Estate Developers' Association of Hong Kong on why prices have risen in the last 15 years. The study will also project prices and demand up to the year 2011. ''I'm not trying to defend developers. But all through history they have been blamed for high prices. Hong Kong has become wealthier and everyone wants to live in the Mid-Levels.'' He said this was one of the most overlooked points of Hong Kong's property debate. ''We have about 1.6 or 1.7 million households in Hong Kong and we have the same number of housing units. So why are property prices going up when everyone has a unit?'' Part of that answer lies in simple statistics. Half of the territory's population lives in homes provided by the Hong Kong Housing Authority while the other half lives in private sector housing. Yet 13 per cent of public housing dwellers also owned a home in the private sector either to rent out or use as an investment, Dr Wong said. He said this was not surprising because overall income levels between public and private sector residents were not far apart. Dr Wong said the drive to seek better housing was strong because public housing living space was about 60 per cent smaller than in private units. He said the redevelopment of existing properties should be a priority instead of churning out sprawling new residential complexes in far-flung corners of the New Territories. While acknowledging such developments provided housing opportunities for young adults who wished to move from their parents' unit, Dr Wong said redevelopment was a better alternative for the growing numbers who demanded large units close to the city centre. A recent government housing taskforce earmarked 120 hectares of land for future housing development and announced that 60,000 new flats would be built over the next six years. ''Sure, you always need more land, but you need better quality units to fulfil the demand of a wealthier population, not just more units.'' The most efficient solution was to redevelop existing structures, building them bigger and better than what stood there before. ''If this is not done, prices will keep going up,'' he added. Dr Wong's report was expected in mid-June but the economist is revising the study to take into account findings by the Government taskforce's report. He would not give a new release date. The report will contain policy recommendations for the Hong Kong Government.