Redesigning a Legacy: 172...

Redesigning a Legacy: 172 New Trees Planted at Seattle’s Climate Pledge Arena

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Key Facts

334 1st Ave N, Seattle,
WA 98109, United States


Climate Pledge Arena

Swift Company
Oak View Group

Climate Pledge Arena Case Study

climate pledge arena


Located within the Seattle Center, Climate Pledge Arena stands as a transformative redevelopment of a historic site originally constructed for the 1962 Seattle World’s Fair which saw over 10 million visitors.

This multifaceted venue proudly hosts the NHL’s Seattle Kraken, the WNBA’s Seattle Storm, and showcases the world's foremost live music acts and events seating up to 18,000 people.

Named The Climate Pledge after an initiative by Amazon and Global Optimism made in 2019, dedicated to achieving global net zero carbon status by 2040. The construction started in 2018 and the grand opening of Climate Pledge Arena took place on October 22, 2022.


The Next Layer of Trees

render of climate pledge arena redesign

Artist impression of Climate Pledge Arena

Landscape architects, Swift Company were able to protect 107 historic and mature trees around the perimeter of Climate Pledge Arena.

With the planting of an additional 172 trees and 38,000 square feet of new trees and plant areas. Swift Company took a successional forest approach where they looked at the already established mature tree canopy on the perimeter of the arena and designed the next generation and layer of tree canopy.

As highlighted by Swift Company Principal, Gareth Loveridge:

“The entire perimeter was about how do we get more green space and tree environments that invite people in. The more trees we get in there, the more benefit we provide for their daily lives.”  

Using Stratavault for Soil Volume

climate pledge 004 stratavault Citygreen

In most urban settings trees struggle to grow to maturity due to lack of space for tree roots and soil volume.

For Climate Pledge Arena, Stratavault soil cells was key to the planting of new urban trees and increasing soil quantity and volume to already established mature trees around the perimeter.

The demand for robust infrastructure necessitates heavily compacted ground, crucial for supporting above-ground structures. However, this compaction restricts access to vital elements—nutrients, water, and oxygen—essential for optimal tree root growth.

As a consequence, tree roots must work harder expanding their tree roots to find suitable nutrients, water, and oxygen to grow which leads to a reduced growth rate and in some cases tree death due to root girdling.

The 100% recycled plastic stratavault matrix works by taking infrastructure load off the tree roots and soil. Giving the tree and soil a more natural uncompacted growing profile when compared to traditional structural soil planting methods.


broken planting bed details stratavault Citygreen

Infographic on how stratavault grows and protects street trees

The Stratavault system increases the total soil volume available to the tree by over 90%, a substantial improvement compared to traditional structural soil methods, which typically allocate only 20% of usable area to soil the tree can use.

Structural Soil vs Soil Cell stratavault Citygreen

Void Space highlights volume available for tree roots

The increase in soil volume helps improve the performance of the tree ensuring that the tree canopy and the range of benefits across environmental, economic, and healthcare are fast-tracked while protecting the infrastructure and tree roots from damaging each other.

Using Stratavault for Climate Pledge Arena also ensured that the landscape architects could plant larger, more established trees thereby further speeding up the results.

Using Stratavault for Stormwater Management

Strataflow Render stratavault Citygreen

Stratavault also allowed Swift Company to innovate their stormwater management design to incorporate green-blue infrastructure with on-site rainfall and stormwater directed into nearby tree pits through strip drains, pervious pavements, and micro grading of the pavement to direct stormwater.

“It lets the ground plane do exactly what we want it to do, and we’re not making compromises”
Gareth Loveridge, Swift Company

example of WSUD elements being used to feed a stratavault tree pit

Strip drain and snorkil to allow water and oxygen exchange

This allows the trees to detain significant waterflows in the stratavault matrix reducing the strain on the city's municipalities during high rain events while improving the growth rate of the trees as the soil and tree roots use the water for increased tree health and canopy development.

“The water cycle in Seattle is dynamic and there’s plenty of times where we want to slow the water down and soil cells really let us do that” 
Gareth Loveridge, Swift Company

Additionally, using soil and tree roots clean the water of pollutants which ensures that water that does trickle through the tree pit back into the city municipalities will be cleaner.


First Stadium to Earn Net Zero Carbon Certification

climate pledge arena green exterior


In October 2023, Climate Pledge Arena lives up to its name and became the first stadium to earn ILFI certification. The energy profile of a stadium is quite complex, from restaurants, sporting spaces, lounges, offices, retail, and public transport. So, the team had to investigate ways to reduce and sequester their carbon footprint across electricity usage waste, and environmental impact.

During the global pandemic, they redesigned the entire facility to be 100% electric & worked with local energy companies to purchase renewable energy credits as Seattle's reliance on hydropower isn’t recognized by ILFI’s standards and will switch to a newly completed solar and wind farm soon.

Across waste they are working with suppliers to stop the use of single use plastics and they estimate that over 95% of waste is saved from landfill.

Tree Canopy, Living walls, and planting initiatives were major considerations for the landscape with over 12,000 plants and trees planted. The added greenery will help sequester carbon and reduce urban heat through shade mitigation and evapotranspiration of the trees and plants' leaves, and help foster biodiversity in the region.


“We have to address issues of heat island effect and temperature, the integration of soil cells into the fabric of the city is essential to being able to build the tree canopy of a city”

Barbara Swift, Swift Company


Climate Pledge Arena is an environmental legacy that serves over 200 events annually and is at the forefront of carbon performance in the stadium and arena space. The valuable addition of 172 trees will continue to grow, shade, and serve the community for decades to come.

People Enjoying Climate Pledge Arena park

Interested in growing your own green legacy? Book a Free Consult with one of our Urban Greening Consultants to find out how.



spacer stratavault Citygreen

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- Laura Wiesenekker, Project Engineer, Densford Civil -

“Citygreen is a very professional  business, and I found everything was great in terms of deliveries, product supply and information. It was all forthcoming and helped us to complete the project.”

- Keith Burns, Architect/Designer, Keith Burns Architect -

“Citygreen offered training and invaluable technical assistance during the works.”

- James Callan, Estimating Manager, Complex Co Pty Ltd -

“Our experience, in working with a Citygreen Design Studio was second to none. We found responses from the design studio to be very timely, and technically thorough. We went backwards and forwards a number of times, looking at different iterations of the design and, nothing was too much trouble to examine and explore different possibilities. I would highly recommend the Citygreen Design Studio to any future client considering using your services.”

- Sandra Smith, Principal Landscape Architect, City Of Monash -

“We are big on compliance on all projects, and the fact that their SmartCertify cloud platform covers all bases, and supports their 20 year warranties, is critical – especially that these pits are being installed under roadways and footpaths.”

- Johny Purkaystha, Civil Program Engineer, Central Coast Council -

"I reviewed all the previous projects that we have installed in the past couple years using your product and I can happily report back that we have 0% mortality in the soil cells, which is incredible!"

- Brendan Wilton, CEO, Trim Landscaping, Bedford, Canada -