Water pooling against your foundation or in low spots? A French drain fixes that. Enter your trench dimensions to get the gravel, perforated pipe, and landscape fabric quantities for the job.
Trench Dimensions
ft
in
in
Scenario: You're installing a 30 ft French drain with a 12-inch wide, 18-inch deep trench.
Result: You need about 1.7 cubic yards of gravel, 32 feet of perforated pipe, and 120 sq ft of landscape fabric.
Calculate the trench volume: length x width x depth (all in feet), then divide by 27 for cubic yards. A 30-foot trench that's 1 ft wide and 1.5 ft deep needs 30x1x1.5/27 = 1.67 cubic yards, minus the pipe volume.
At least 18 inches deep for yard drainage. For foundation drains, dig to the bottom of the footing. The drain should slope at least 1% (1 inch drop per 8 feet of length) toward the outlet.
4-inch perforated PVC or corrugated drain pipe is standard for residential French drains. The holes face downward so water seeps into the pipe from the gravel, not from above. Use solid pipe at the end for the discharge run.
Yes. Wrap the entire trench with landscape fabric before adding gravel. This prevents soil from silting into the gravel over time, which would clog the drain. Use a heavy-duty non-woven fabric, not the thin weed barrier type.
Want to learn more before you start your project?
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