Lawmakers passed the Basic Housing Units bill on Friday, making it mandatory for owners of subdivided flats to register their properties and meet relevant standards.

These include a minimum floor area of eight square metres, a separate toilet and at least a window for each unit.

Homeowners can register their units starting in March.

Those who complete the registration within the one-year period given to owners of subdivided flats will be granted a grace period of 36 months to carry out rectification and apply for accreditation, giving them a total of 48 months.

Secretary for Housing Winnie Ho said that as landlords have 48 months to bring their flats up to the required standard, this would prevent flats being taken off the market at once and causing rents to spike.

"Rent levels have always been closely tied to market supply and demand," she said.

"If more public housing applicants have more reasonable housing options, the demand for subdivided flats will fall.

"Therefore, it is expected that once the regulatory regime is rolled out, subdivided flat rents will have limited room to increase significantly."

The HK$3,000 accreditation fee for each unit will be reduced or waived if homeowners complete the alteration and rectification works by the end of the grace period in February 2030.

Ho added that the government would ensure subdivided flat tenants would not lose out on a place to stay due to the new law.

This will be done by allocating other resources like transitional housing units in a flexible manner and helping them look for homes in the private market.