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Silva Cell projects come in all shapes and sizes. The common ground between all of them is the advantages that having enough planting soil does for the long term health and survival of street trees. In combination, the trees and soil also act as a powerful form of green infrastructure, helping to reduce the amount of stormwater runoff that enters nearby sewers, stormwater conveyance facilities, and creeks, thereby protecting properties, infrastructure, water quality, and creek health.

To get started incorporating Silva Cells into your site, we recommend the following steps and resources.

1. DETERMINE PROJECT GOALS
  • If you haven't already, familiarize yourself with the basics of how the Silva Cell works. For any immediate questions, contact your local sales representative:

    For projects in the United States, email This e-mail address is being protected from spambots. You need JavaScript enabled to view it or call 415-781-9700.
    For projects in Canada, email This email address is being protected from spambots. You need JavaScript enabled to view it. or call 604-687-0899.
    For projects in the United Kingdom, email This email address is being protected from spambots. You need JavaScript enabled to view it or call (+44) 020 3848 4230.
    For projects anywhere else in the world, email This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

  • Determine the target soil volume per tree using the "How Much Soil To Grow a Big Tree?" chart as a guide.

  • Determine how many trees on your site will need Silva Cells.

  • If you want to use the Silva Cell for stormwater treatment, download the Stormwater Estimating Worksheet to estimate roughly how many Silva Cells will be needed to meet your treatment goal. Stormwater management always needs to be done within the requirements of governing agencies and using standard civil engineering practices. The specific design of the system should be refined with project modeling.

    • NEW! If your project is located in western Washington, download “Using the Western Washington Hydrology Model (Version 4) to Size Silva Cells for Runoff Treatment and Flow Control”. These guidelines provide step-by-step instructions on how to use the model to properly size Silva Cells and calculate stormwater credits for treatment and flow control. The credits are equivalent to a bioretention facility, allowing you to get the most stormwater credit and greatest value from your Silva Cells!

      If your project is located in western Washington and you are only sizing Silva Cells for runoff treatment, not flow control, you may alternatively download Using the Western Washington Hydrology Model to Size Silva Cells for Stormwater Filtration. These guidelines provide step-by-step instructions on how to use the model to properly size Silva Cells and calculate stormwater credits for treatment (only) based on an equivalent sand filter facility. Note that this method may be slightly more simple to follow for new modelers, but will provide less stormwater credit than the above method based on equivalent bioretention due to lack of accounting for native soil infiltration.

    • NEW! If your project is located near the Seattle-Tacoma area in Washington State, you may use simplified sizing equations (coming soon) to expedite preliminary sizing of Silva Cells to meet stormwater treatment and flow control requirements. This tool provides a rule-of-thumb guide for designers and reviewers to estimate the number of Silva Cells needed based on the presence or absence of an underdrain, maximum depth of ponding (or depth of air gap), and native soil infiltration rate. Final design of flow control and treatment facilities needs to be performed by an Engineer using an approved continuous model (see above guidelines). This website will be updated with the simplified sizing equations soon!

    • Stormwater management always needs to be done within the requirements of governing agencies and using standard civil engineering practices. If sizing Silva Cells to fully or partially meet stormwater minimum requirements, an Engineer is typically required to perform calculations in accordance with local Codes and standards.

To maximize value, we recommend the following design guidelines

  1. Include the soil in the tree openings themselves as well the soil in adjacent open space accessible to the tree when calculating the total available soil volume in the area of work.
  2. Since each stack of Silva Cells needs one deck -- regardless of whether you are using the smallest post (1x), the mid-size post (2x), or the tallest post (3x) -- it is more economical to design a deep system than a wide system.
  3. Provide approximately 1,000 ft3 (28 m3) of soil for a canopy tree and 600 ft3 (17 m3) of soil for an understory tree. Stormwater treatment volumes will vary based on project location and goals.
  4. Always make tree openings as large as possible. This is the least expensive way to provide the tree with soil, and larger openings will accommodate the size and trunk flare as the tree matures.
  5. Wherever possible, use Silva Cells to link tree openings to each other or to existing nearby soil volumes, such as parks or lawns. Trees that share soil need less overall soil per tree than those in isolated soil volumes.

2. PLACE SILVA CELLS ON YOUR SITE
Now that you have estimated the number of Silva Cells you will need on your site to meet your project goals, you can begin to place them on your site plans. Or, for a small fee, we are happy to complete a Silva Cell layout for you. These and other design services may be helpful throughout the development of the project. Contact us at This e-mail address is being protected from spambots. You need JavaScript enabled to view it to find out more.

  • First, refer to the Silva Cell System Layout Instructions for a step by step tutorial on laying out Silva Cells on your project site plans.
  • After reading the Layout Instructions, we recommend that you refer to the AutoCAD video tutorial for a hands-on demonstration of the layout process.
  • We provide a Silva Cell "block" (under "Design Documents"), which is available in different units, in AutoCAD format for ease of completing a Silva Cell layout and final material counts.
  • Read about the 5 most common mistakes made on layouts before beginning your own layout in order to save time.
  • To complete your drawing package, incorporate Silva Cell sections that reflect your design.
  • Standard and Supplemental Silva Cell details are provided in AutoCAD format. These can be used to illustrate standard Silva Cell component parts, dimensions, and pavement profiles.

3. CREATE A SILVA CELL SPECIFICATION
To complete project documentation, incorporate Silva Cell specifications.

  • We provide specifications for both the Silva Cell and our recommended soil mixes.
  • Soil is extremely important to the success of your trees and your stormwater management goals. Proper soil selection is a large topic that is way more complex than we have room to discuss here. We do offer tree and soil design services; please contact us at This e-mail address is being protected from spambots. You need JavaScript enabled to view it for further information or to receive a quote for this. To read more about soils, we recommend referring to James Urban's book,Up By Roots.
  • If you are using bioretention soil mix to fill the Silva Cells and receive optimum stormwater credit for treatment and flow control, see Section 6.1.2.2 of the 2012 Low Impact Development Technical Guidance Manual (DRAFT).

4. BUDGET PRICING
The Silva Cell has many possible configurations, and there are no one-size-fits-all pricing guidelines. Costs will vary based on characteristics of the site, the quantity of frames and decks required for the project, the tree size and stormwater treatment goals, and the design objectives. Remember that each frame is 48'' (1200 mm) long x 24'' (600 mm) wide x 16'' (400 mm) high and holds about 10 ft3 (.28 m3) of soil.

According to bid tabulations from projects across North America, the Silva Cell system generally costs $14 - $18 per cubic foot installed (that estimate includes everything except the base course, the final paving and the tree itself).

For cost efficiency, we recommend the following design guidelines:

  • Include the soil in the tree openings themselves as well the soil in adjacent open space accessible to the tree when calculating the total available soil volume in the area of work.
  • Decks and frames are priced differently, and frames are less expensive. Since each stack of Silva Cells needs one deck — regardless of how many frames there are — it is more economical to design a deep system than a wide system.
  • Provide approximately 1,000 ft3 (28 m3) of soil for a canopy tree and 600 ft3 (17 m3) of soil for an understory tree. Stormwater treatment volumes will vary based on project location and goals.
  • Always make tree openings as large as possible. This is the least expensive soil you can "buy," and larger openings will accommodate the size and trunk flare of a mature tree.
  • Wherever possible, use Silva Cells to link tree openings to each other or to existing nearby soil volumes, such as parks or lawns. Trees that share soil need less overall soil per tree than those in isolated soil volumes.

Contractors, please This e-mail address is being protected from spambots. You need JavaScript enabled to view it or call (415 781 9700) for an estimating worksheet.
For price information specific to your project, contact us (This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) for a quote; we'd be happy to assist you.