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Case Study - Crawl Space Banner

Case Study - Crawl Space

Rainwater was seeping down into the soil and entering the crawl space of this single family residence. The result was a very wet crawl space with mold on the beams and subfloor. The design we decided on was a French drain with a moisture barrier.

The crew has excavated a trench whose depth is well below the elevation of the crawl space floor. The white material between the trench and the house is a very thick plastic membrane that will help direct any water flowing laterally across the trench to the bottom where it can enter the pipe. Filter fabric is being readied in the yard before it is installed on the yard side of the trench to keep the surrounding soil from entering into the system and mixing with the gravel backfill.

The gravel backfill is almost complete. The filter fabric lining the trench will be folded over on top of it, totally enclosing the system. Note that the downspout is connected to a pipe as well. In this application, we wanted to remove the roof water from the area as quickly as possible, so it was connected to solid pipe which sloped to the street. It is important that it not be connected to the perforated French drain pipe, because that would unnecessarily introduce roof water to the surrounding soil that is supporting the foundation. Typically, it is best to allow the roof water with its tree and roof debris to flow out of the downspout, and onto a splash block where it can leave most of the debris behind before it flows into a nearby catch basin.

This photo shows the cutouts at the curb for this system. A pump had to be used for the deep French drain protecting the crawl space, and its 2” PVC discharge pipe is the smaller of the two holes in the curb. Rather than increasing the workload on the pump by connecting the downspouts to it, because the water in them originates at a higher elevation (the roof), it can be piped directly to the street. The larger hole in the curb is the downspout discharge pipe outlet.

The system is complete. The gravel backfill has been brought to the surface and the pump lid (which needs to be cleaned off) has been installed. Note the metal edging retaining the gravel near the plants.

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