OTTAWA — The planned renewal of Parliament Hill's West Block, including a new building in the courtyard, passed a milestone on Friday with approval of the design by the National Capital Commission.

"Public Works can now proceed with wrapping up the tender documents and getting this building built," said Linda Dicaire, chief of federal design approvals for the NCC.

The design features a pavilion in the centre of the courtyard, as well as three new underground levels. A glass roof will cover the courtyard. When finished in 2019, it will become the temporary chamber for the House of Commons during renovation of the Centre Block, which is expected to last five to seven years.

"West Block must embrace this new role and provide a dignified chamber," Dicaire told the NCC.

When work in the Centre Block is complete, the space will be converted to committee rooms.

The $863-million West Block renovation includes masonry restoration, seismic upgrades and new windows and roof. It will remove asbestos, install new mechanical systems and create a new visitors' entrance.

It is part of a 25-year, $5-billion plan to upgrade the Parliament buildings.

"We are a very young country," said NCC chief executive officer Marie Lemay. "We have to protect the heritage we have. Moving the House of Commons is not an easy challenge. West Block is the critical first step in implementing the plan."

Preserving views of the Parliament buildings was an important design consideration for the infill, explained Dicaire. The roof projects slightly from the courtyard but will be barely visible on the skyline.

The choice of a glass roof preserves the open character of the courtyard, gives natural light and provides views of West Block's heritage facades, she said.

"The span is very considerable," she added. "Maybe the greatest design challenge was how to support it."

The roof will rest on treelike steel columns and the pavilion itself.

The project is being carried out by two Montreal architecture firms in joint venture, Arcop and Fournier Gersovitz Moss Architects.

There is a "sense of openness, lightness and verticality within the infill," said Dicaire.

She called it an elegant design with a "contemporary Gothic expression" and compatible to the West Block.

The designers have considered technical aspects of the roof for weather, ventilation and heat gain and loss, she added.