An Environmental and Engineering Marvel

By Greg Huber

Being chosen by Oak View Group, a Seattle public-private partner and developer, to redevelop the former Key Arena into a brand-new, best-in-world venue and the future home of National Hockey League’s Seattle Kraken and  Association’s Seattle Storm, all while keeping its historic landmarked roof intact, has been one of Mortenson’s most challenging and rewarding undertakings. 

As if this alone wasn’t enough of a challenge, a whole new bar was set when Jeff Bezos from Amazon tweeted in June 2020, “I’m excited to announce that Amazon has purchased the naming rights to the historic Seattle arena previously known as Key Arena. Instead of calling it Amazon Arena, we’re naming it Climate Pledge Arena as a regular reminder of the urgent need for climate action. It will be the first net zero carbon certified arena in the world, generate zero waste from operations and events, and unclaimed rainwater in the ice system to create the greenest ice in the NHL. #ClimatePledge.”

At the time of that announcement, the project team had already carefully planned every aspect of the arena. The structural foundations and building excavation were well on their way, the procurement team was ordering necessary construction components and discussions with local utility companies were underway about how to power the building’s operational needs. 

Although sustainability was always an important feature to be incorporated into the project, this new goal – to create the first net Zero Carbon certified arena in the world – was the biggest challenge yet. Luckily, Mortenson and the entire team’s passion and competitive spirit drove them to determine how – not if – this could be done. The certification by the International Living Futures Institute is the most rigorous benchmark of sustainability in the building environment. It is the gold standard against which all others are measured. People from around the world use its regenerative design framework to create spaces that give more than they take.

Structural Challenges

The first major challenge was determining how to “recycle” the 44-million-pound historic roof (designed by Seattle architect Paul Thiry. Meanwhile, the construction crew excavated 600,000 cubic yards of dirt underneath to substitute for the arena’s Y-column and buttresses that held up the historic roof. This was held by seventy-two temporary roof support (TRS) steel columns; each founded 70 to 90 feet below the existing arena floor level. The TRS system also had to resist seismic loads and limit movement to a quarter inch. Mortenson used water jets to remove concrete from the base of the old columns which exposed the steel rebar to allow the team to safely cut and extend the column foundations that were supported nearly 100 feet below grade.

The process occurred during most of 2019 and used nearly the amount of steel equal to a modern-day Major League Soccer stadium. Mortenson relied on intense team collaboration, top-down construction, and digital tools to simulate the built environment. And today, Climate Pledge Arena is standing on the original 20 Y-columns and four pronged-buttresses to hold up the roof, originally built for the 1962 Seattle World’s Fair.

In addition to maintaining the roof, Mortenson was charged with saving the iconic glass curtain wall that every fan, visitor, and Seattleite will see walking by Climate Pledge Arena, while preserving the view of the Space Needle, cityscape, and more. To accomplish this, each glass panel had to be carefully marked, catalogued, and stored before reinstallation in its original location.

Working towards Net Zero

Climate Pledge Arena is working to be the first net Zero Carbon arena in the world, powered exclusively by renewable energy rather than natural gas. The arena will run solely on electric power for daily operations, eliminating all fossil fuels from the building and utilizing the first all-electric dehumidification systems in the NHL. This meant Mortenson had to replace natural gas infrastructure with electrical systems. From kitchen systems and concessions, to air handling units, and building conditioning – all systems were changed to be served by electricity instead of natural gas.

Overall water usage is critical to limiting energy use and sustainability goals. Rainwater will be stored in a 15,000 gallon below-grade cistern and filtered as needed for the “rain to rink system.” Waterless urinals and low flush fixtures were added to increase water usage efficiency.

The mechanical, electrical and plumbing (MEP) system was also designed with efficiency in mind. Energy recovery ventilators, serving all the locker rooms, collect 100 percent of the air that is exhausted and use the captured energy to preheat or cool the incoming air streams. 

Changing out gas to electrical conversion substations almost doubled the amount of electricity coming into the building, requiring more electrical equipment. With equipment in order, immediate decisions were needed. Luckily important changes were able to be made at the fabrication stage, and the custom electrical equipment production stayed on schedule. 

Next, situating heavy electrical gear presented a real space utilization conundrum. Mortenson and the design team needed to determine where the equipment was going to live. Typically, it’s located on the first floor, but construction sequencing hindered that possibility. The entire construction and design team needed to find the best location that was cost and schedule efficient and required the least amount of rework, which resulted in a substation on an elevated metal deck.  

Renewable Energy

The original 160,000 square-foot arena roof is historic and, as such, could not be used to host solar panels. Instead, solar panels are planned to be installed on the roof of the new atrium building entrance and on the facility parking garage. The energy generated by the solar arrays will be used to power to arena alongside additional renewable energy sources. 

Project Delivery

The construction and design team used several tools to ensure design, construction and marketing efforts dovetailed together to create a seamless project delivery. Mortenson used 4D building information modeling (BIM) as a basis for multi-trade coordination and scheduling. The entire building was constructed virtually to aid with major trade system coordination. For instance, the steel team could use the model to track fabrication and installation tasks. Color coding was used to aid schedulers while tracking procurement, upcoming tasks, and completed work. Using the 4D model, the MEP systems were modeled to not only assist in clash detection (field installation coordination) but also in prefabrication efforts.

Changing horses in midstream to create a net zero arena was a major effort by the entire team. Mechanical and electrical contractors were essential in giving their input, as were the architecture and engineer teams that jumped in to determine construction sequencing. 

Climate Pledge Arena will be a beacon of corporate responsibility across the sports landscape. Together, Mortenson and Oak View Group are setting new sustainable standards for the built environment and inviting others to join The Climate Pledge to reduce carbon emissions for a better future. 


Greg Huber is Project Executive at Mortenson. 

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