We now know the scope of the new arena at Seattle Center after updated figures were released at a public presentation at Pacific Science Center Tuesday night.

The new arena at Seattle Center is expected to be 800,000 square feet, according to the latest plans released by architects on Tuesday night.

The scopes and new diagrams were released during a public presentation at the Pacific Science Center. Project executives showed their complex plans as part of a new speaker series called the "Science of Sports and Entertainment," including such intricate details as the air conditioning system, and how the Oak View Group plans to protect the historic KeyArena roof.

"This is not a renovation," said Project Executive Shaun Mason, of the roughly 200 people at the Paccar Theater. He said the current plans involve digging down 15 feet, "down and out in four directions."

Mason said the group has already done exploratory drilling to make sure construction crews can build out the complicated design, which he said will essentially at one point involve "propping up" the roof while excavators do their work.

"Like building a ship in a bottle in a lot of ways," Mason told the audience. "This is a major undertaking, the likes of which have never been done before."

The size of the project is roughly doubling the current KeyArena footprint.

There has already been work done inside the existing KeyArena bowl, and heavy machinery is now staging outside the existing building. The new arena is scheduled to open in the spring of 2021.

Geoff Cheong, the lead project designer for Populous, said there have been other tweaks to the design. The grand atrium will be smaller than originally planned, as to not overtake the historic roof. The loading dock entrance will be "53 feet below grade," according to Cheong.

Jeff Sawarynski, the Senior Principal with ME engineers, joked "Day one, I don't know how I'm going to do this," but said behind the scenes there had been significant attention to detail.

He pointed to the cooling and dehumidification systems because the "NHL wants it cool and dry." He said many arenas include "massive equipment on the roof," but because of the historic roof design, there will be five near grade 'snorkels" to allow for air flow in and out of the arena.

The National Hockey League awarded a franchise to Seattle to begin play in the 2021 season, a year later than originally discussed. League leaders had been concerned that the complicated project could be pulled off in time for 2020.

NHL Seattle CEO Tod Leiweke said the team's training facility and headquarters at Northgate are in final design-planning now.

The arena is now projected to cost $850 million in private financing, and the cost has continued to grow as the design has been tweaked.

The presentation is the first of many planned as part of a joint venture between the Pacific Science Center, NHL Seattle, and the Oak View Group.

Will Daugherty, Pacific Science Center CEO, said he hopes the speaker series occurs on a bi-monthly basis and feels like the idea of mixing sports and science is a natural fit. "This is just one step in a great collaboration."