Canadians will elect 338 MPs on Monday, up from 308 in the last election.

It's the largest leap in representation in Canadian history. But while our number of MPs may be growing, our historic buildings aren't.

A team of architects was brought in to figure out this puzzle, whose urgency and significance were made clear from the outset. Although the specialist firm of conservation architects worked on the design for two years, it only had from the time the election was called in August until election day to install the new seats. 

"There was no wiggle room in this project, we had to deliver on time with no extension.… I mean, we're intervening in the seat of government. It's huge," says Rob Martin, of the firm Robertson Martin Architects.

When the House of Commons was rebuilt after a fire in 1916, the chamber was constructed with room to grow. There were 245 MPs then. The nearly dozen times the number of MPs has grown since, Parliament was able to squeeze in a few more desks.

But the chamber reached its limit at 308. To fit 338, a redesign was needed. Otherwise, Canada might face a situation like the one in Britain, where MPs are stacked cheek by jowl on busy debate days in Westminster.

'The chamber is steeped in history and tradition and we had to respect that.' –Rob Wright, Public Works and Government Services Canada

"People sit on top of you. Literally, they sit on top of you," says Andy Percy, a British backbench Conservative MP. 

Winston Churchill had the option to expand the British House of Commons after it was badly damaged during the Second World War. But he instructed it to be rebuilt on the same scale.

"Churchill liked the bear pit feel of it … when there's a big vote or major debate you get lots of people crowding in," says Percy.

But bear pits can make for ornery MPs. Canada wanted a less ursine solution.

Theatre seating saves room

The watchword of conservation architecture is invisibility. The historic building had to be transformed, while looking exactly the same.

House of Commons theatre seats

Some of the new seats in House of Commons are fold-down, theatre-style seats. (CBC NEWS)

The architects came up with a design that involved taking out the back two rows on each side of the chamber. They replaced the two-person desks with longer desks shared by five to seven MPs. In the second-last row, to save space, the regular seats were replaced by drop-down theatre seating.

Some MPs are growling about the redesign.

From the start, Bob Rae was against the Fair Representation Act — the legislation passed in 2011 that added the 30 seats. He felt the number of MPs should be capped at 300. He also doesn't like the idea of two different styles of seating.

"We've never lost the sense that everybody's got the same status and everybody's got the same position in the House … whether you're the prime minister or a newly elected rookie."

MPs can be sentimental about their seats. James Rajotte, an Alberta Conservative MP who just retired, is following a House tradition and buying his seat to take it with him. He hopes to pass it on through generations of his family.

"It is the most significant part of the House of Commons to me … that is where I actually sat for nearly 15 years.… it represents those hundreds of thousands of people back home," he says.

Rob Wright, assistant deputy minister for the Parliamentary Precinct Branch, co-ordinated the project for Public Works. He stresses that every MP still has equal space in the House, and that the theatre seating interfered less than other options would have with the way Parliament works.

House of Commons with 338 seats

The House of Commons redesign to fit 338 MPs includes the addition of fold-down theatre seating in the back rows. (CBC News)

There were other options such as putting seats into the centre aisle or in the corridors on both sides of the chamber. But these would have impeded access routes.

The ceremonial opening of Parliament would have been difficult with someone's desk and chair blocking the way.

"Adding 30 additional MPs was no easy task," Wright says. "The chamber is steeped in history and tradition and we had to respect that."

'Ship of state'

Every detail, down to the stain on the woodwork, was carefully considered. The new five- and seven-person desks are built to the same standard as the original two-person desks. The House of Commons shop was used to reproduce old-fashioned joinery, in some cases using 150-year-old tools.

The team at Robertson Martin Architects refers to the House of Commons as the "ship of state" and points to hidden seafaring references inside the chamber. The wood, brass and green carpet all reflect a nautical feel. 

New House of Commons seating prototypes

Heritage specialists built the seats to best reflect the original 1920s design. (Public Works)

Matching that historic green carpet was a conundrum. The fabric was thought impossible to replace, until an old English loom was found with some remnants on it, and weavers were able to recreate the carpet.

Even with the heritage flourishes, the project came in on time and under budget, at $2.5 million.

The redesign may just be a temporary measure. In 2018 MPs will move out of the House of Commons to the West Block for at least a decade while the Centre Block undergoes a multimillion dollar restoration.

At that point Parliament could opt to throw out tradition and radically redesign the chamber.