Speaker Vicki Dunne has informed members construction work in the North Building, across Civic Square from the Assembly, will begin in September and be completed by January 2016.

Work will then move to inside the Legislative Assembly building with a planned completion date of mid-2016. Offices and public areas of the building are being reconfigured to allow for an extra eight members after the 2016 election, bringing the total to 25 seats.

As part of the push for more space inside the 1961 building, some support staff and members of the Office of the Legislative Assembly are set to be moved to nearby government-owned buildings.

A concept design brief by Cox Architects for the renovation included plans for three new office suites for government ministers, three new suites for backbenchers and the opposition, exhibition spaces, and shared meeting areas.

The $10 million project will also see new shower rooms and kitchenettes added to the at-capacity building, and about 30 staff will be impacted.

Mrs Dunne said a project control group had been established with Chief Minister Andrew Barr, overseen by Assembly Clerk Tom Duncan. It will ensure the project is finished on time and without budget blow-outs.

The group includes Mr Barr's chief-of-staff, Jamie Driscoll, and Mrs Dunne's senior adviser, Clinton White, as well as project management experts and observers.

Some staff from the government's Justice and Community Safety Directorate will relocate from the North Building to Moore Street, while the ACT National Trust has recently moved to new premises in the Griffin Centre.

"In May this year, expressions of interest were invited from the construction industry to undertake the fit-out works for both the North Building site and the Assembly building," Mrs Dunne said.

"From that process a shortlist of firms, all of them reputable quality firms, were invited to lodge a formal tender for the works. The tenders have been evaluated, the territory is currently in the process of conducting pre-contract negotiations with a preferred tenderer."

Mrs Dunne said an early priority would be an agreed site plan to enable the works to proceed with minimal disruption. The firm will be announced once contracts are signed.

She warned territory politicians to expect disruption from the construction work and said she would provide quarterly updates to the Assembly.

In May, design briefs for the work showed sleek contemporary features, with new offices and meeting areas to include warm lighting, refined joinery and state-of-the-art technology. Only construction firms with experience in building or renovating secure and sensitive government buildings such as parliaments, courts, museums and galleries are being considered for the contract.

The brief called for "recessed warm lighting within discreet, refined joinery", glazed partitions with window graphics for privacy and to allow natural light, small meeting spaces, tea areas with bench seating and "professional carpet colours".

An expanded meeting room is expected to replace two offices currently used by ABC journalists on level one, while the Canberra Times office, media conference room and disused members' lounge will go to make way for three new members' suites.

Members and staff working in the new Assembly will have access to the new shower rooms, complete with "elegant, timeless finishes" to maximise the sense of light, functional layout with natural materials, and large shower cubicles with glass doors.

The Legislative Assembly first moved to the former South Building in 1994.