Many designers understand the need for the Silva Cell and support it as an effective design tool for tree growth and stormwater management in urban environments. Yet, all too often it gets value engineered out of projects for being too pricey. While cheaper than creating a custom suspended pavement system, and actually money-saving in the long-term, the system’s up front costs are often more than many people expect or are willing to pay.
Here are some design rules of thumb to reduce the cost of Silva Cells on your project — without depriving the trees of the soil they need.
- Go down rather than out. 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.
- Make large openings. 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.
- Share soil volumes. 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.
- Calculate “free” soil. 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.
For rough estimates, public bid tabulations from completed projects in North America put the Silva Cell system costs at between $14 – $18 per cubic foot of soil installed (that includes everything except the base course, the final paving and the tree itself).
Each Silva Cell installation is unique to existing site requirements. Costs will vary based on characteristics of the site, the quantity of product required for the project, the tree size and stormwater treatment goals, and the design objectives.
Designers, please email or call (415 781 9700) us to discuss your project parameters and arrange for a free plan review.