A minimum area of at least 100 square feet, including the toilet and kitchen, as well as ensuring proper ventilation and drainage, were among the recommendations made by the Hong Kong Institute of Surveyors in its report to a government task force on subdivided units.

Various fire protection measures should also be implemented, the institute noted, including no open flame cooking, partition walls installed between units that could block fire for at least one hour, as well as providing a clear fire escape route.

Other recommendations include having at least one openable window towards open space and separating the kitchen and toilet properly.

The institute estimated that about 30 percent of the 110,000 subdivided flats in the city do not meet these minimum standards and require improvements.

Kenny Tse, who chairs the institute’s Building Policy Panel, said that generally it would only cost owners tens of thousands dollars to improve their flats, adding that almost all upgrades could be carried out without affecting the building's common area.

“All the proposed enhancements should be carried out within the subdivided units, not related to the common areas. For example, the fire service installation, we only need to buy a fire extinguisher, smoke detector or something like that,” he said.

“For the drainage part, this is the only one they need to connect to the common drainage pipe, but I think that this is feasible and also easy to carry out."

The institute also proposed a registration system for subdivided flats, saying owners must entrust professionals to inspect and accredit the units. Such inspection has to be conducted every three years.

But it said owners of sub-standard units should be given 12 months to make improvements.

“We have to take care of the over 100,000 subdivided units in existing markets and we think that we cannot treat the 100,000 subdivided units at one time,” said Nathan Lee, who heads the institute’s Building Surveying Division.

“So we should allow some time for the owners to take care of the existing tenants and also provide some relocation for the existing tenants. So we propose 12 months for the modification period.”

The institute added these were just temporary solutions and the ultimate solution to the subdivided unit issue remained increasing public housing supply.