Under the current laws, you can apply to have an illegal structure approved for the same price as an ordinary development application.

But a Legislative Assembly committee running the ruler over the ACT's flawed development application processes has been told retrospective approvals were being used to bypass scrutiny from neighbours.

The Inner South Canberra Community Council told the committee retrospective approvals seemed to be routinely granted, even when "questionable" claims were made by applicants that they were ignorant of the requirements.

"Licensed builders and architects who regularly seek retrospective approvals should not be gaming the system and any examples of compliance avoidance should be considered in license renewals," their submission said.

"Granting retrospective approvals should require a written explanation of how the situation has arisen and limited approvals should be granted, e.g. emergency work to provide structural support from unforeseen issues. There are, for example, simply too many cases where plot ratios are exceeded - which disadvantages law-abiding developers - and other questionable practices occur."

The Planning Institute of Australia's ACT division told the committee its members who worked within government felt the numbers of retrospective development applications were increasing as a result of developers wanting to avoid the process.

"There is common knowledge among the development industry that the ACT government is not strong on compliance," it wrote in its submission.

"The DA Compliance team is within Access Canberra, not within ACTPLA and this may give rise to the belief that proponents can risk any compliance action against works undertaken without approval."

However, its members who worked as consultants felt if the unauthorised work was minor, it was fair to correct it through a retrospective development application.

"It seems futile to require a proponent to demolish, say a minor structure, and then re-erect that structure when development approval was granted. Particularly if there was a strong likelihood that approval could and would be granted," the institute said.

Anne Forrest from the Inner South Canberra Community Council said there should be steep fees for people who applied for approval for a building after it was constructed as a deterrent.

"Retrospective approval cannot be challenged, so as people are pointing out it sets a precedent and it then enables others to do the same thing and there’s a rolling effect to all of that," Ms Forrest said.

Woden Valley Community Council president Fiona Carrick said there needed to be incentives and disincentives in place in the development application process.

"If a building goes up prior to the DA when they know it's outside the rules there should be a penalty for doing that because that’s a disincentive for other people to do it," Ms Carrick said.

However an ACT Planning Directorate spokesman said only a small percentage of development applications were approved retrospectively.

"During the last five financial years a total of 179 retrospective DAs have been approved or approved with conditions. This compares to a total of 5530 approved development applications in the merit track over the same time period," he said.

The number of retrospective approvals has fallen from 43 in 2013-14 to 33 in 2017-18.

The spokesman said retrospective applications are only approved if the project is consistent with the territory plan.

Planning Delivery Division executive director Brett Phillips told the committee two retrospective development applications had been refused recently.

"Both have been subject to compliance activity after the refusal by Access Canberra. My understanding is one resulted in a partial demolition and the other related to a home business on the premises that had to relocate," Mr Phillips said.

ACT Chief Planner Ben Ponton said he was aware of a number that had been refused.

"It tends to be partial demolition rather than full demolition, I can think of a parapet that was too high and they had to cut the parapet," Mr Ponton said.

The inquiry continues.