Large Scale LEED Net Zero Stormwater Retention For Irrigation Re-Use And Potable Water Source

An 85,000 gallon RainSpace stormwater retention chamber was installed on a narrow residential lot in Los Altos, California. Sandwiched between the rear of the residence and an existing swimming pool with a garage to one side, this RainSpace Chamber was the first part of a backyard improvement project which includes a patio, water feature, lawn and flagstone walk installed over the RainSpace. The RainSpace Chamber allowed a large water storage capacity without losing the utility and esthetics of the surface area. Water is collected from the rooftops of the home, garage and pool cabana and from the adjacent pavements and directed through a pre-filter into a combined inlet/overflow pumping well. The collected stormwater is used to irrigate the landscape and for potable water in the home. The stored stormwater is passed through a water purification system as it enters the house.

The owner's objectives were: (1) to achieve "net zero" water usage from the connected municipal utility, enjoying the benefits of naturally soft rainwater without latent pharmaceuticals or treatment chemicals typically present in municipal water systems; and, (2) to have a water supply that is earthquake proof at this Northern California site - the RainSpace is flexible, not rigid, the surface load is carried by a multitude of horizontal structural core tube bundles with no vertical structural components to move out of alignment and the stored water is closely contained within the tube cores to eliminate dangerous sloshing of the large water mass.

This RainSpace installation was configured to fit into a constricted space with a surface footprint and underground profile designed to maximize the water storage capacity while staying outside of the load bearing soils of the adjacent buildings and swimming pool. Old specimen trees on the property were also a major consideration in designing this RainSpace. The RainSpace excavation included a mid-depth bench along two sides of a "T" shaped pit, with the remaining walls at an 11 foot depth. This created a complex void space that maximized the utility of the available footprint between the pool, garage, house and specimen trees. The site access was restricted with only a long 8 foot wide driveway and the installation required special care to avoid damaging the existing landscaping and structures.

Los Altos, California