The UK's second biggest housing firm does not have an agreed minimum standard for all the homes it builds, an independent report has found.
A report into Persimmon says that a lack of a group build policy increases the risk of defects in its houses.
Persimmon has been under pressure after a number of buyers complained about the safety of its homes.
The review found that some houses did not have fire-stopping cavity barriers or they had been wrongly installed.
It said that the issue of missing or improperly fitted cavity barriers was "a systemic nationwide problem", which it said was "a manifestation of poor culture coupled with the lack of a group build process".
Persimmon's chairman Roger Devlin commissioned the report in April after complaints emerged about the quality of its new homes.
One couple, Phil and Nicola Bentley, said that they had discovered 700 defects in the Persimmon home they paid £280,000 for in 2017.
The independent review into Persimmon, led by barrister Stephanie Barwise QC of Atkin Chambers, said that there were no agreed procedures to supervise or inspect its employees or sub-contractors' work and that staff were only given limited training.
It recommended that the firm "should take sufficient time to formulate and embed a 'Persimmon Way' of building".
It also said that the company's corporate culture needed to change.
Persimmon's former chief executive Jeff Fairburn was forced out last year amid criticism of a pay deal which awarded him £75m.
'Confront difficult truths'
Mr Devlin said that the "very thorough and comprehensive review" "found that Persimmon had focused on policies around inspections immediately before and after the sale of a home, rather than those governing build quality inspections".
"In my view, this is one of its central findings and I am encouraged that the company is already embracing the review's recommendations in this area through significant operational investment and procedural change," he said.
Ms Barwise said: "The board of Persimmon deserve significant credit for commissioning this review and publishing its findings.
"It demonstrates their willingness to confront some difficult truths as they focus the business on rapid change and improvement.
In February, the company announced that its annual profits had passed £1bn for the first time - up from £966m in 2017.
At the time, a source close to Housing Minister James Brokenshire said the minister was "increasingly concerned" by Persimmon's practices, including its use of leasehold contracts, the quality of its buildings and its leadership.
He said this meant its inclusion in the Help to Buy scheme was under review.