Silva Cell’s Allow Trees to Thrive in Parking Lots

DeepRoot is key to the growth of urban forests everywhere for everyone to enjoy. Parking lots and car parks have not traditionally been designed with the health and longevity of trees top of mind.

DeepRoot’s Silva Cell is intentional in creating more space and accommodating more soil where it is most imperative: at a tree’s roots. For trees to thrive more than a few years, their roots need to grow deep and wide. The weight of cement or pavement can be suspended by Silva Cells. Silva Cells are especially vital to trees in parking lots as a car’s weight is a major source of pressure on the roots over time. According to the EPA, the average weight of a car is 4,156 lbs (1,884 kg). The Silva Cells bear the brunt of the weight so the trees’ roots do not have to.

Silva Cells are engineered to support pavements up to AASHTO H-20 Standards, while allowing for vast amounts of lightly compacted soil within their matrix.

Silva Cells are made of virgin plastics, which means they are strong, reliable, and durable. They are created to last decades and are a key component of the success we’ve had for more than 15 years.

Below are some of our favorite parking lot and car park projects spanning from 2008 to today.

Stoneleigh Elementary School | Towson | MD

Stoneleigh Elementary in Maryland is a flagship K-5 school of the Baltimore County Public School system. The county and the state are particularly stringent in terms stormwater management requirements, as they are in the Chesapeake Bay Watershed, an EPA NPDES phase 3 river system. In order to comply with run off regulations, all the while not losing any parking spaces, Site Resources used 240 double stacked DeepRoot Silva Cells to filter and otherwise treat the rain water sheet flow from the parking lot which enters the cell though porous concrete. The added co-benefit  of large trees and summer shade in the parking lot is a good example of sound practice when designing stormwater management systems. Over 500 ft3 of soil volume per tree has given the 12 trees and their roots substantial soil volume to thrive. Nearly ten years later we can see these trees are thriving in the parking lot, because of the dual action Silva Cell’s contribute toward water management and tree health.

*Stoneleigh Photo taken by Sam Smith in October 2020

Quick Facts:
240 2X Silva Cells
500 ft3 (14 m3) of soil volume per tree
12 trees
Installed in 2013
Project Contractor: Roy Kirby & Sons, Inc.
Project Designer: Site Resources Inc.

Walmart Parking Lot | Lakeland | FL

Chris Hice (Kimley-Horn and Associates) walked the site in 2008 envisioning large, flourishing trees to provide canopy coverage for the redesign of the parking lot. He knew that the only way to grow trees that big was to provide them with access to sufficient high-quality soil. Kimley-Horn wanted to achieve at least 50% canopy coverage over the parking area and to maintain an adequate number of parking spaces. Originally, trees were installed in 4’ x 4’ diamond-shaped parking islands with little additional soil to promote healthy growth or longevity. Hice recommended Silva Cells as a part of the tree protection and landscape plan for the site. Creating a strategy to ensure healthy site trees was imperative and a great addition to the existing green development strategy. In addition to helping cool and clean the air, the trees and their soil volumes would help manage stormwater on-site and reduce runoff consistent with low-impact development practices. The size of the parking lot was nonnegotiable, so the only way to get more soil for the trees was to find a way to put good soil underneath the pavement.

Quick Facts:
800 2X Silva Cells
1,000 ft3 (28 m3) of soil volume per tree
16 trees
Installed in 2008
Project Contractor: Cleveland Construction
Project Designer: Kimley-Horn and Associates


Eugene O’Neill Drive | New London | CT

The coastal town of New London, Connecticut, received an upgrade in urban forestry and an increase in tree canopy in 2016. A poorly functioning parking lot in the heart of downtown was replaced with a new lot that improved circulation and increased capacity to 200 cars. Twenty-five trees line Eugene O’Neill Drive and surround the parking lot, which is near various transit sites. The trees are on their way to reaching a full canopy. When they do, they will provide ample shade and mitigate urban heat island effect. Eugene O’Neill Drive and Green Street run parallel to the Thames River in the heart of the city. New London is a multimodal transit city; residents use ferries, trains, buses, and cars to commute to major metropolises like New York or Boston. In 2017, The design of the lot, which spans two city blocks, was focused around Complete Streets initiatives, to reduce traffic speed and improve pedestrian access and safety while beautifying the main arterial road leading into the city. Design elements include stormwater infiltration swales, plantings, public art, and, most important, 44 shade trees. See more details in our project case study.

Quick Facts:
324 2X Silva Cells
348 ft3 (10m3) of soil volume per tree
44 trees
Installed in 2016
Project Contractor: Colonna Concrete & Asphalt Paving
Project Designer: Kent + Frost Landscape Architecture


 Bethel Transit Terminal | Sherwood Park | AB

The Bethel Transit Terminal is a bus transit hub, park and ride, and parking lot in Sherwood Park, Alberta. Just outside of Edmonton, the Bethel Transit Terminal has over 1,100 parking spaces and is the main transit commuter hub between Strathcona County and the city of Edmonton. Catering to public transportation needs and demands, the terminal was upgraded in 2013. The upgrades included green infrastructure that mitigates heat island effect in the warm summer months. Just over 120 trees were planted in parking islands with 940 3X Silva Cells. On average. each tree received 15m3 of soil volume to support deep roots growth and offer protection from the weight of thousands of cars and heavy pavement.

Quick Facts:
940 3X Silva Cells
530 ft3 (15m3) of soil volume per tree
126 trees
Installed in 2013

Project Designer: Morrison Hershfield – Calgary
Project Contractor: Aman Building


 Mitchell Library | Palo Alto | CA

In 2011, Palo Alto’s Mitchell Library underwent reconstruction nearly 50 years after its original construction. Renovated inside and out, the Mitchell received a fantastic green infrastructure upgrade. The space is LEED Platinum certified and strives to educate the community on the facility’s sustainability features. The space reduced potable water use by 40%. Below the 14 trees in the library’s parking lot are 390 3X DeepRoot Silva Cells providing each tree with over 994ft3 of soil volume. The Silva Cells are in seven different spots across the area and go three stacks deep (3X). Our technical manager, Pat Greeley, recalls the installation by Park West being especially well done saying, “This is the most level base I’ve ever seen!” The level base ensures the decks of Silva Cells snap onto the frames easily.

Together the bioretention from Silva Cells and the pervious paving treat 100% of rainfall that falls on-site. The project highlights the commitment to the community and the environment for the long term.

“Our goal for the Mitchell Park Library and Community Center was to create a sustainable, artful, and lush environment that welcomes the community while providing ecosystem services. With under-pavement Silva Cells in the parking area, we were able to meet that goal by expanding the root zone from the narrow water quality basin—creating the best conditions for healthy tree growth and providing additional stormwater retention capacity. The trees are thriving, carrying the park-like feel through the entire site.” -Kimmy Chen, Gates + Associates, Associate Principal

Quick Facts:
390 3X Silva Cells
994 ft3 (16m3) of soil volume per tree
14 trees
Installed in 2011
Project Contractor: Park West
Project Designer: Gates + Associates


SMUD HQ | Sacramento | CA

In 2019, the Sacramento Municipal Utility District (also known as SMUD) headquarters renovated its architectural space as well as its outdoor landscape. The goal was to prioritize creating a landscape that works as a place and for people. The 400 employees who work at SMUD will have a supportive tree canopy in their parking lot for decades to come. This complements the green interior and LEED gold certification. Nine trees that line the perimeter of the parking lot are supported by 252 2X (stacked) Silva Cells. Because the landscape architects, Callander Associates, chose to prioritize soil health and tree health, these trees will grow large and strong. Each tree has 688 ft3 of soil volume supporting it.

Quick Facts:
252 2X Silva Cells
688 ft3 (19 m3) of soil volume per tree
9 trees
Installed in 2018
Project Contractor: BrightView
Project Designer: Callander Associates


3045 Park Blvd | Palo Alto | CA

In Palo Alto’s California Avenue district, just minutes from Stanford University, is the three-year-old, 1.3-acre office space 3045 Park Blvd.

The office building has a companion parking lot that can accommodate 70 parking spaces for employees. The space is inventive and replete with green infrastructure. The property is LEED Gold certified under LEED V4. The building is all electric with no natural gas and sources its energy from 100% renewable resources available in Palo Alto. The construction process practiced best management, including diverting waste to a recycling facility, prioritizing soil volume throughout the process. During construction, polyethylene covers were placed over stockpiled soil and sand prior to storms. Soil was also stabilized primarily through paving, mulching, and planting in areas where construction activities and traffic had ceased. Soil volume is held and retained below 16 trees around the parking lot on the site. DeepRoot Silva Cells are being used for both supplementing tree growth and treating water on-site. The parking lot is 70% impervious, and stormwater is treated using the combination of bioretention and Silva Cells.

The trees showed good growth in their first two years since planting. With the 326 ft3 of soil volume per tree that the Silva Cells provide, the plantings are on track to grow into a large canopy that combats heat island effect.

Quick Facts:
186 2X, 54 3X Silva Cells
326 ft3 (9.2 m3) of soil volume per tree
16 trees
Installed in 2019
Project Designer: DES Architects & Engineers
Project Contractor: McGuire and Hester



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