How do I know if my French drain is clogged?

Common signs of a clogged French drain include standing water above the trench after rain, saturated soil near the drain line, water surfacing along the trench during storms, and little to no flow at the discharge outlet. If your basement or crawlspace moisture problems have returned after being resolved by the drain, clogging is a likely cause.

How long do French drains last before they fail?

A properly installed French drain with clean washed aggregate, appropriate geotextile fabric, and correct slope can last 15–25 years or more. However, drains installed without filter fabric, with unwashed gravel, or in heavy clay soils may begin failing in as little as 2–5 years due to sediment clogging.

Can a clogged French drain be repaired without digging it up?

In some cases, yes. If the clog is limited to the pipe interior, high-pressure jetting through cleanout access points can clear sediment and root intrusion. However, if the gravel bed surrounding the pipe is saturated with fine soil particles, the aggregate must be excavated and replaced for the system to function properly again.

What type of gravel is best for a French drain?

Clean, washed, angular crushed stone in the 3/4-inch to 1-1/2-inch range (ASTM #57 or #2 stone) is ideal. The aggregate must be free of fines—dust, sand, and clay—that would reduce void space and accelerate clogging. Avoid pea gravel, unwashed pit-run gravel, and round river rock.

Should French drain holes face up or down?

For subsurface groundwater collection, perforations should face downward (4 and 8 o'clock positions) so water rises into the pipe from below while minimizing sediment entry from above. For surface runoff collection through a gravel bed, perforations facing upward or to the sides can work, but proper geotextile filtration is essential regardless of orientation.

Why is my French drain not draining water after heavy rain?

The most common causes are a clogged pipe or gravel bed, a blocked discharge outlet, insufficient slope, or the system being overwhelmed by a water volume it wasn't designed to handle. Start by inspecting the discharge point for obstructions, then check cleanouts for standing water, which indicates a downstream blockage.

Why French Drains Fail: Clogging, Sediment & Bad Installs

Discover why your French drain is clogged or not working. Learn the top causes of failure—sediment, poor installs, bad grading—and how to fix them. Expert guide.

By Low Point Labs

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