In its place, independent "clerk of works" should be used to oversee the construction of a new home or development. according to waterproofing expert Ross Taylor.

Mr Taylor made the recommendation during the fifth day of public hearings at the assembly's building quality inquiry, which is examining the problems besetting Canberra's construction boom.

In the ACT, certifiers, who inspect sites at different stages of construction to check compliance, are appointed by the owner of the land. In the case of multi-storey developments, that means the developer is responsible for hiring the certifier.

The model has been heavily criticised throughout the inquiry amid concerns it gives rise to potential conflicts of interests.

A number of submissions to the inquiry suggested either the government or owners be responsible for appointing certifiers, in order to avoid situations in which developer might hire a certain practitioner because they would deliver a favorable assessment.

On Wednesday, Mr Taylor said rather than tinkering with the existing scheme, such as increasing the number of inspections required during construction, the model should be abolished entirely.

"Just start again, it's just so fundamentally flawed with regards to building defects," Mr Taylor said.

Mr Taylor, who has inspected dozens of high-rise Canberra developments in the past decade, agreed that the model created the potential for conflicts of interest between developers and certifiers.

"It's the golden rule - the person that holds the gold makes the rules. That absolutely applies to certifiers," he said.

"I've actually heard people say that you cannot be too difficult with the developer otherwise you won't get the gig."

Mr Taylor said another significant problem was that the average certifier typically did not have the technical skill and knowledge to recognise a design or construction flaw.

"The certifiers very often come in for half an hour before a major pour," he said.

Mr Taylor said in place of private certifiers, the ACT government should revert back to using "clerk of works" - an industry professional who oversees construction work on behalf of the building's future owners.

The clerk of works would be entirely independent of the builder or developer.

Certifiers should still have a role, but it would be limited to managing paperwork associated with various approvals, Mr Taylor said.

Concerns about the existing model were also raised by Vista executive committee member Julian Matos during his evidence to Wednesday's public hearing.

Mr Matos said it was "mind-blowing" that developers were able to hand pick which certifier inspected their property.

"If the certification is paid for directly by the developer, surely that opens the door for corruption?" Mr Matos said.

The inquiry continues.