July start to parliament security upgrade

Work to fortify Parliament House against an increased terror threat will begin in July.

Officials from the Department of Parliamentary Services appeared at a Senate committee on Thursday to answer questions about a security upgrade for the 27-year-old building.

Design changes to the ministerial wing, which include a new perimeter fence, gatehouses and bulletproof glass are still being finalised.

Work though will begin on July 9 - during parliament's mid-winter break - with construction expected to take 23 weeks.

Archival-quality photographs have been taken in and around the building.

"In the event in the future that we need to reverse any of the works if at all possible ... we'll know exactly what it needs to look like," the department's first assistant secretary Neil Skill told senators.

The department is consulting the building's principal architect Romaldo Giurgola, but through a lawyer because he is unwell.