It must have seemed like a good idea at the time to build guardhouses at the four corners of Parliament Drive.

The placement has a medieval feel, like turrets keeping watch on a palace - and perhaps that's why their mission failed.

The guardhouses were abandoned years ago but now two new gatehouses will be built at Parliament House as part of a $108 million security upgrade.

The issue of the disused and dusty guardhouses was raised during the first public hearing by a Senate committee conducting an inquiry into the work to fortify the building against terrorism, including a 2.6 metre high steel fence screening the ministerial wing that houses the office of Prime Minister Tony Abbott.

ACT Senator Katy​ Gallagher said it seemed odd to have empty guardhouses when more than $100 million was being spent on security improvements.

"There is no-one in them, there is dust and a heater if you are looking for one," she said.

"There are four [guardhouses] dotted around that I have never, ever seen used. Seriously, there are 1989 phones in there, push-button phones."

The hearing was told the original guardhouses were sited at the corners of Parliament House to allow an officer posted there to view both axes of Parliament Drive.

Neil Skill from the Department of Parliamentary Services said it was not possible to simply relocate the old guardhouses as the new ones would be designed for screening people if needed.

"It is pushing the perimeter out so we could screen officers or visitors at that point if it is chosen to do so," he said.

"What is on the corners of Parliament Drive certainly would not provide the level of protection for occupants that we are looking for."

The Senate inquiry was established when Independent senator Nick Xenophon and the Labor opposition combined to refer the question of parliamentary security to the committee for urgent investigation.

The inquiry will provide oversight for the work on the new perimeter fence, gatehouses and bulletproof glass which will begin on July 9, with construction expected to take 23 weeks.

The inquiry is to pay particular attention to security and safety considerations, project management, value for money, design integrity, heritage impacts and the moral rights of the building's architects, and impacts on building occupants and visitors.

It is believed further physical security enhancements are under consideration including widespread installation of bulletproof glass and more security fencing, possibly screening the Senate and House of Representatives wings.

Archival-quality photographs had been taken in and around the building in case the work ever needed to be reversed, senators were told.

The new "perimeter security enhancements" follow the highly visible upgrading of Parliament House security, including the deployment of heavily armed Australian Federal Police officers outside and inside the building, after the national counter-terrorism alert level was raised last September and the Canadian Parliament was attacked by a gunman in October.

The head of the Department of Parliamentary Services Carol Mills, who was fired from her position last month, was found by the finance and public administration committee to have presided over an organisation that was "deeply dysfunctional".

Mr Skill told the hearing a project of this size and scale had not been undertaken at Parliament House since the building was constructed in the 1980s.

"DPS also acknowledges that concerns have been raised, predominantly through this committee, that DPS is perceived to have a poor record in delivering building construction and security projects, and although significant steps have been taken to improve this capability, the change process is still ongoing," he said.

Scrutiny of the department's management of the project was being done by an independent auditor and through "project in-flight audit reviews", he said.

Senator John Faulkner has called DPS the "worst run government department in the Commonwealth of Australia".