A businessman's iceberg home plan collapsed in a pile of rubble after attempts to install an underground playroom and bedroom backfired.
The five-bedroom detached London home, which was sold in October for over £1 million, collapsed in the middle of the night.
Kingston Council claimed the work may have been carried out without the approval of local building control inspectors and the incident had been reported to the Health and Safety Executive for further investigation.
Photographs showed the remains of the home, which was listed in April last year for £1.15 million, with windows and doors left in a pile after hundreds of bricks gave way.
The home near Kingston Hill, south west London, was empty when the building collapsed around 1am on Monday morning.
House prices in the street, set between Richmond Park and Wimbledon Common, average £1,375,000.
A planning permission request for the property, submitted by Omar Alajaji, included the demolition of a swimming pool, conservatory and outbuilding on the property.
Mr Alajaji also sought permission to build an iceberg basement, a two-storey side extension and to increase the height of the roof.
Councillor David Cunningham, Cabinet member with responsibility for regeneration at Kingston Council, said: "The owners of this building submitted a building regulations application just two days ago and have therefore carried out works without our guidance and approval.
"Our primary concern is to ensure that the building is structurally safe. We are working with the contractors to carry out the work, which is due to complete by the end of the day.
"Following this, we will be reporting this incident to the Health and Safety Executive for further investigation."
A woman who lives next door to the house which collapsed said her family were rushed out of their home in the early hours of the morning.
Sharon Gouhar said the family were woken by a "big bang", which made her children's rooms shake and left clouds of dust around the house.
Ms Gouhar, 55, said: "Last night in the early hours, at about 1.30am, we heard a big bang which made me jump up.
"My kids' rooms shook a little bit so they jumped up too, my daughter ran in asking what had happened, and when my son went downstairs he saw that part of the house had collapsed.
"We had such a shock, the dog started barking, and when I looked out through our balcony it was all dusty.
"The emergency services got us to come out of the house and not go back for a while, so we threw on some clothes and tried to find somewhere else to stay.
"We tried to get a hotel but we have a dog, and it's the Easter holidays, so in the end we slept in our office."
Mr Alajaji, a Saudi Arabian, bought the property for £1,150,000 last year.
Ms Gouhar, a cafe owner, said she knew the home had recently been sold, but was unsure what work was under way.
She added: "I know it was under construction but I don't know much about it and everyone around us is building.
"My neighbour was saying that an Arabic family have bought it but I've not seen them.
"Builders come and go, and they had recently taken the whole roof off the house, so I don't know if they were going to put up another floor."
A spokesman for thr London Fire Brigade said: "Firefighters attended a house collapse on Derwent Avenue, Kingston Vale in the early hours of this morning.
"The majority of the two-storey house collapsed.
"An extensive search was carried out and thankfully it appears that no one was in the property at the time of the crash."
Police said nobody had been hurt during the incident.
A Metropolitan Police spokesman said: "The matter has been referred to the London Borough of Kingston-upon-Thames."