The project, 1101 W. El Camino is a newly constructed 52-unit condominium community located in the heart of downtown Mountain View, CA, which happens to be the home base of Google. The project is designed by Jett Landscape Architecture + Design, and installed by Regis Contractors.
California (and much of the West Coast) has introduced stormwater quality requirements on large new construction projects, commonly referred to as C.3 Stormwater guidance. This requires that all water coming off constructed environments be filtered through bioswales and bioretention areas to improve water quality. You’ve probably seen these kinds of filtering areas within parking lots and around buildings. You can learn more about the requirements at this website.
One common strategy used by architects and landscape architects is to introduce bioretention planters onto the structure of the building, which otherwise would have taken up footprint at ground level. These planters have traditionally been very large, cast-in-place concrete areas susceptible to waterproofing and drainage failure. They need to be large to filter the substantial amount of stormwater draining off the roof and exposed areas. Tournesol Siteworks has been working with designers for several years on developing pre-cast bioretention planters that serve the same function.
Typically a bioretention planter is at least 42" deep, which allows for 12" of gravel, 24" of filtering soil media, and 6" of freeboard area to accommodate the drainage from the drain lead. You can get an idea of how this works in the images above and below. Drainage from the pre-cast planter may be channeled out by a plumbed drain line (as seen above) or may be drained from a scupper to an on-ground planting area.
Pre-cast bioretention planters are typically made of lightweight GFRC concrete. The live loads on the sidewalls of these very large planters typically demand the rigidity and strength of concrete (although we're investigating the use of FRP fiberglass right now). The units may be used individually or ganged together to filter a larger area.
Tournesol Siteworks has been developing, with input from our design customers, strategies for connecting stormwater planters, both together and to typical drainage plumbing. The product compares very favorably, both in terms of footprint and ease of installation, with both cast-in-place concrete and build-in-place CMU construction. Because these are becoming ever more common, we're putting our project teams to work on these projects on a regular basis.
The planters shown here all use custom decorative brass hardware. Tournesol Siteworks has developed standard non-decorative solutions for both connecting planters as well as drainage.
1101 W. El Camino is an excellent example of this type of use of on-structure bioretention - we'll look forward to providing you with more applications using this same solution soon!