French Drain Installation in Penryn, California

Underground downspout extensions are highly recommended if water currently pools near your foundation, you have basement moisture issues, or surface extensions create trip hazards or drainage problems. Burying drains moves water 10-20 feet (or more) from your foundation, completely eliminating pooling and foundation risk. While more expensive than surface extensions ($15-$25/ft vs $5-$10/ft), underground systems are invisible, permanent, and provide superior protection for your home's foundation.

A French drain collects water that's already in the ground or standing on the surface; an underground downspout line carries roof water that's already been captured. A French drain is perforated pipe in a washed gravel bed wrapped in filter fabric, built to let groundwater seep in along its whole length. A downspout line is solid pipe with no perforations, because the last thing you want is roof water leaking out beside the foundation. Connecting a downspout straight into a French drain is a common mistake—it floods the gravel bed with far more volume than it was sized to infiltrate.

A properly built French drain lasts decades; a poorly built one clogs within a few years. The difference is almost entirely filter fabric and aggregate. Fabric has to separate soil from the gravel bed so fine particles can't migrate in and silt up the voids, and the aggregate has to be washed and correctly graded rather than screenings that pack tight. Root intrusion from nearby trees and inadequate fall are the other two failure modes. We install with fabric on all sides of the bed, washed aggregate, consistent slope to the outlet, and a clean-out so the line can be serviced later.