WATCH company Stelux Holdings is spending $200 million to redevelop its headquarters building in San Po Kong, Kowloon, into a modern 24-storey facility. The Stelux Building, the headquarters of the group's manufacturing since it opened in 1972, will be rebuilt as an industrial and ancillary services building. ''The existing 13-storey structure will be replaced by a modern 24-storey facility to fill a gap in the high-end industrial office market,'' said Mr Joseph Wong, executive director of Stelux. ''The new building will offer a net area of about 262,000 square feet with a typical floor of 10,900 sq ft. Floor layout has been designed so that it may be sub-divided to offer more flexibility.'' The redevelopment is based on a plot ratio improved from 11.1 to 15.1, which is permitted without further payment of land premium to the Government. ''Once the board has given its final approval to proceed with the redevelopment programme it will take approximately six to nine months to relocate existing operations and demolish the building, and a further 18 months to build the new facility,'' Mr Wong said. Stelux would occupy several floors of the building to house some watch assembly operations for regional and export requirements, he said. Although the more up-market products would still be assembled in Switzerland, he said a significant proportion of watch assembly operations would relocate to China for cost efficiency and to allow sales to the domestic market there. Yee Hing Co, a major shareholder in Stelux, yesterday announced that it had raised its stake in the firm to 51.31 per cent from 48 per cent.