The ACT branches of the construction union and Master Builders Association say unlicensed contractors are undercutting qualified tradespeople, and delivering the type of shoddy building work plaguing new developments across Canberra.

Several trades - including architects, waterproofers, carpenters, painters and concreters - do not require licences in the ACT.

However, architects are registered under the Architects Act 2004.

In a submission to the ACT Assembly's building quality inquiry, the Construction, Forestry, Mining, Maritime and Energy Union's ACT branch secretary, Jason O'Mara, said the introduction of license requirements for more trades would improve building quality.

"It is very clear that these currently unlicensed trades have been the cause of many of the
major issues eroding building quality in the ACT," Mr O'Mara's submission read.

"It creates inherent problems for the quality of the job being completed, as it allows an individual without the necessary skills to complete building works which require a level of expertise that can only be developed through becoming licensed."

Mr O'Mara said in the submission that builders and developers hired unlicensed contractors to cut costs, which undercut skilled and qualified tradespeople.

He said the standard of waterproofing work in new developments had suffered in the absence of mandatory trade licensing.

Master Builders Association of the ACT chief executive Michael Hopkins echoed the union's concerns, saying waterproofing was an "obvious" trade that needed greater regulation.

Contractors need to hold a licence to undertake waterproofing work in New South Wales and Queensland, although no such requirement exists in Victoria.

"With the majority of work performed on a modern day construction site completed by trade contractors, we believe it is important that the companies actually performing the work hold a license," Mr Hopkins said.

“Ultimately licensing provides an accountability mechanism for government to mandate a minimum regulatory standard and take enforcement action if required. This is necessary to restore the community’s confidence in the ACT building regulatory system."

Engineers Australia also raised concern about inadequate waterproofing in its submission to the parliamentary inquiry, which was established in April amid concern about the poor quality of building work in new developments across Canberra.

The peak body said builders' supervision of waterproofing work was "either poor or non-existent", while the materials used were often unsuitable for the Canberra climate.

"Some products used for balcony membranes are unsuitable, poorly applied or impossible to cure during a Canberra winter," the submission stated. "The contract documents often contain no specification for seals or membranes, so the cheapest products are often used."

The assembly committee conducting the building quality inquiry has now received 59 submissions ahead of the November 30 deadline.

The submissions have detailed numerous accounts of water leaks at new properties, construction delays and broke builders leaving homeowners thousands of dollars out of pocket.

On Tuesday, it published 20 new submissions, including feedback from the Combined Community Councils of the ACT.

The submission said builders and developers should be forced to build new dwellings to the exact specifications of display homes, which prospective buyers typically inspect before purchasing.

"People who buy project dwellings, either single or multi-unit, off the plan, make their decision based on the display dwelling," the submission stated. "There is a certain deceit or even fraud where the same quality of finish is not replicated in the final dwelling."

Asked whether the ACT government would consider introducing licences for architects and various trades as recommended by the CFMEU, a spokeswoman for ACT Building Quality Minister Gordon Ramsay said the government was considering revisions to building licence categories, as well as the regulation of people who provided building plans and specifications under our existing building reform program.

It was the responsibility of a licensed builder to ensure work complied with the building code and that the people undertaking the work had the right skills and were properly supervised.