Homes built by one of the UK's largest developers were constructed without essential barriers to slow the spread of fire.
Regulations dictate the flame-resistant material must be installed in roof spaces and wall cavities.
Housebuilder Persimmon Homes found it was missing from some properties on estates in south-west England.
It has written to more than 1,000 people to say their homes need to be checked.
One resident in Truro, Cornwall, said his house "is potentially a massive fire risk".
The homeowner, who did not want to be named, said recent inspections of his five-year-old house revealed "a vast amount" of fire were barriers missing.
"I'm extremely concerned because I have a family, including two children, living in this house," he said.
Some of the homes affected are on a Persimmon-built estate in Exeter where a fire last year "rapidly escalated" as it spread between properties.
Speaking about the blaze, Cornwall councillor Dulcie Tudor said it had spread "through to the roofs of the adjoining houses".
Homes without cavity barriers "act like a chimney" in the event of a fire, she said, and called for work on all Persimmon Homes developments to be halted until the faults have been rectified.
Fire safety consultant Alan Cox said blazes "could easily travel from one compartment or property to another" if there were missing barriers "at roof level".
Persimmon's website says it builds 16,000 new homes a year.
A spokesperson said the firm had "identified this as an issue in its south west region" and had "carried out a full check of more than 1,100 timber frame properties and checks are ongoing".
"However, while investigations are live we are not in a position to advise of the results".
Persimmon includes Cornwall, Devon, Somerset, Bristol, Gloucestershire, Wiltshire and Dorset within the south-west region.
The company did not confirm whether there were any issues in other parts of the country.
Cornwall Council said its enforcement powers were limited because it had not inspected the homes when they were built.
Repeated breaches of building regulations can result in the developer being taken to court by a local authority.
Have you been affected by similar issues to those raised in this story? If so please get in touch at PlymouthNewsOnline@bbc.co.uk.