The house is in The City Pin Klao estate on Phutthamonthon Sai 2 Road, which was built by listed developer AP (Thailand) Plc.
User "Nga Ging" posted the information of the popular Pantip.com web board along with pictures of the structural failure, saying the collapsed roof fell from about three metres about 9pm.
The tangle of metal and roofing tiles damaged a car parked below owned by the father of the house owner.
Nga Ging said he had been living in his house for over three years.
He took photographs of the collapsed and drooping structure showing five extension bolts that seemed to be too small to support its weight, according to comments posted.
Netizens blamed the collapse on the use of bolts they said failed to meet specifications and poor installation.
The house owner said he complained to the developer, who on Thursday morning sent staff to investigate the incident. The company helped clear away all the debris and promised to make repairs and pay compensation for the damage to the car.
Marote Vananan, chief commercial officer of AP (Thailand) Plc, said on Friday that the company has tried to handle the case swiftly. The first priority was to ensure the repairs are done quickly whether the structural warranty was still valid or not.
Generally, housing developers provide a five-year warranty for housing structure. In this case, the project was built about seven years ago.
Mr Marote said the company will send a team to inspect all houses in the project to ensure no repetition of the incident. The initial review of the construction blueprint showed that the engineering design was right about using the correct extension bolts, but the builders put the bolts in the wrong places, weakening the structure.
He said AP (Thailand) has tighten its policy on construction quality, changing from the usual housing construction system, under which one contractor is hired to build the whole house, to awarding subcontracts to specialists in specific areas.
“Over the last 4-5 years, we have given roof jobs to companies specialising in roofing, and are doing the same for other parts of the houses to improve the quality. About 80-90% of housing developments since then have been built this way," said Mr Marote.
It is the second recent complaint about substandard construction of dwellings. In late August the owner of a condominium sold by another listed developer, Sansiri Plc, found his condo wall was stuffed with haphazardly dumped styrofoam, cardboard, candy wrappers and other construction workers' rubbish.
The developer, though a bit late in responding, promised to inspect the other units in the condominium development.
Mr Marote said such publicity of faults in housing construction shows the growing strength of consumers. He thought this would encourage developers to lift their game and ensure they were providing quality products to customers.
One commenter on the Nga Ging post, using the account name kan_pat, also complained. She said she bought a 15 million baht house from AP (Thailand) three years ago and faced problems with water leaks and cracks in the walls which has not yet solved.