A five-by-13 metre (16-by-43-foot) structure was found on the lowest podium of No 70, as well as a five-by-six metre basement behind it.
At No 72, an unauthorised basement with a 17-by-19-metre floor space was found underneath the property. A part of the retaining wall along the slope was also illegally demolished to make room for basement windows.
There was also an illegally built swimming pool below the house.
It is currently unknown whether a third property, No 74, which was also affected by the landslide, also has unauthorised modifications.
The Buildings Department said on Tuesday night it would apply for a court warrant on Wednesday to enter No 74, after the owner refused to allow its officers to enter parts of the house.
2. Does the city have a problem with illegal home modifications?
Under the scheme, reported unauthorised structures could be kept temporarily if they were deemed safe by a qualified person, with checks expected every five years. But risky structures had to be demolished.
Vincent Ho Kui-yip, former president of the Hong Kong Institute of Surveyors, said that although the city had a problem with illegal structures at homes, there had been a marked improvement in recent years.
“Fifty years ago, building controls were not so stringent, so many people would make adjustments to their properties,” he said, adding residents would add air-conditioning units, canopies, rooftops, shelters and extra rooms.
“One issue now is that people make the most of the adjustments inside their homes, making it harder for authorities to spot them.”
Ho criticised what he called “tedious legal procedures” that might have hamstrung further efforts to fix the problem.
“The difficulties of entering private premises to conduct investigations has resulted in government enforcement action becoming ineffective,” he said.
Ho noted property owners delaying punishment by going through lengthy appeal processes had also fuelled the issue.
“The penalties or fines imposed by the court are unable to deter illegal works, which could have hindered attempts to stamp it out,” he said.
3. What high-profile cases have there been in the past?
In 2018, then secretary for justice Teresa Cheng Yeuk-wah joined a long list of officials caught red-handed over unauthorised building works.
The structures included a rooftop, basement, horizontal extensions on the ground floor and glass canopies outside their car parks.
Poon was fined HK$20,000 after he was found guilty of having an unauthorised pool in his garden.
In February 2012, former chief secretary Henry Tang Ying-yen, who was running for the city’s top job at the time, admitted there was an unauthorised basement at his luxury residence in the Kowloon Tong district.
The basement was dubbed “an underground palace” that included a wine cellar, home cinema, gymnasium and Japanese bath. Tang avoided punishment but his wife, Lisa Kuo Yu-chin, was ordered to pay HK$110,000.
What does the law say?
According to the department, anyone who intends to carry out alterations and additions should consult professionals for advice and make a formal application for approval and consent from the Building Authority.
Such works include linking floors, adding staircases, removing units or walls, modifying means of escape or adding barrier-free access.
Adjustments carried out without prior approval and consent are classified as unauthorised building structures.
Offenders face a maximum penalty of one year’s imprisonment and a fine of up to HK$200,000 (US$25,530). For continuing offences, there is a further daily fine of HK$20,000.
“It’s not just a matter of violating the rules, it’s also a matter of safety,” lawmaker Lo Wai-kwok said. “What we have seen is [that illegal structures are] extremely dangerous.”
Lo said that he was not sure whether residents had not understand the dangers of illegal building works or that they did not know the consequences of being caught.
“Either way, it’s really stupid,” he said, adding the law clearly stated what kind of work and alterations could be carried out.
“If procedures are not followed, everyone, including the contractor, can be punished,” he said.