In the third such incident in three months, a slab of plaster fell 12 storeys from the top of a Housing Board block in Hougang on Sunday morning.
No one was injured by the slab, a piece of the facade measuring 1.2m by 0.6m. The facade had been checked recently, according to the estate manager, Ang Mo Kio Town Council (AMKTC).
Resident Andy Loh, 39, heard a loud noise around 11am on Sunday.
"I went down to check and saw all the (plaster) scattered on the ground," he said. The slab seemed to have hit a lorry parked nearby and dented its roof, added Mr Loh, who is a sales manager.
Mr Gan Thiam Poh, Member of Parliament for the area, was doing house visits nearby when a resident told him the news. He visited the block around noon and alerted the relevant authorities.
"I suppose it could be related to the heavy downpour. Practically every day, there has been heavy rain," he said.
The area has been cordoned off.
The Building and Construction Authority (BCA) said one of its engineers has inspected the damage and assessed that the block's structural integrity is not affected.
The block dates back to 1991 and comprises 60 executive maisonettes.
An AMKTC spokesman said the town council has engaged a professional engineer to carry out detailed investigations. "The facade of the incident block and surrounding blocks will be inspected as well. Follow-up repair works will also be done on the affected area," he added.
Checks in preparation for ongoing works such as repainting had failed to flag the possibility of falling plaster.The checks, carried out by a professional engineer, included thermal checks for conditions such as excessive moisture and degradation of material, and visual checks and tapping on walls to find cracks and hollows.
"However, these checks were unable to detect potential falling plaster," said the spokesman.
Residents hope further incidents can be prevented.
"It was quite scary, because I think the impact could have killed someone," said assistant operations manager Shalene Lee, 37.
"For us with kids, we will definitely be more worried," she added. Her son and daughter, aged seven and eight, often play downstairs.
A spokesman for HDB said it is in touch with Ang Mo Kio Town Council over the matter.
Earlier this month, the BCA said it was looking at ways to improve the safety of building facades.
This was after a piece of facade fell from a 51-year-old block in Circuit Road last month - also after heavy rain - and a sunshade in Tampines was partially dislodged in September. No one was injured.
Such facade elements are not structural parts of a building and are not covered by the BCA's regular Periodic Structural Inspection.
Facade parts are the responsibility of town councils and should "remain safe" with regular and proper maintenance, said the BCA.
Plaster falls from HDB block in Hougang.