Come next year, contractors working on Housing Board flats would not only need to be accredited, but also possess trained workers.

The tightening of this regulation was revealed in a HDB statement on Thursday.

Currently, HDB flat owners who want to renovate their property are required to find a registered contractor, as well as seek the agency's approval before works begin.

In some cases, the untrained workers jeopardise key structural walls during the hacking works.

"(This) will affect the structural integrity of the building and potentially endanger the safety of residents in the building, including the family members of the flat owner," said the HDB.

Every year, HDB receives close to 60,000 renovation applications.

Starting next year, registered contractors would need to have two workers certified by the Building and Construction Authority if there is demolition involved.

These trained workers would have gone through a course that teaches the theoretical and practical aspects relating to hacking, and costs $195 per person.

"Trained workers will be able to recognise the danger of hacking structural walls and mitigate the risk of such incidents from happening. The new course would help to raise the professionalism of the renovation industry as a whole," said the HDB.