French Drain Inspection

Trench minimum 12" wide and 18-24" deep. Perforated pipe with minimum 1% slope. Pipe holes face down. Gravel bed above and below pipe.

1. Verify trench depth — minimum 18" for landscape drains, deeper for foundation drains

2. Check pipe slope — minimum 1% (1" drop per 8 feet)

3. Verify perforated pipe has holes facing down (collects groundwater from below)

4. Check gravel bed — minimum 2" of clean gravel below pipe and 4" above

5. Verify filter fabric wraps the gravel (prevents soil from clogging gravel)

6. Check pipe diameter — 4" minimum for residential

7. Verify clean-out access points at bends and every 100 feet

- Pipe holes facing up (collects surface water instead of groundwater)

- Insufficient slope — water sits in pipe

- No filter fabric — soil migrates into gravel and clogs system

- Trench too shallow

- No clean-out access

- Wrong gravel type (must be clean, washed stone — not crusher run)

French drain must have a positive outlet. Daylight outlet, dry well, or connection to storm system. No dead-end drains.

1. Verify drain has an outlet — must go somewhere (daylight, dry well, or storm system)

2. Check outlet is lower than the inlet (positive drainage)

3. Verify outlet is protected from animal entry (rodent screen)

4. Check dry well (if used) is properly sized for the expected water volume

5. Verify no dead-end pipe segments

6. Check that outlet does not discharge onto neighbor's property

7. Run water into the system and verify it exits at the outlet

- No outlet — drain fills up and becomes useless

- Outlet higher than inlet — water backs up

- Dead-end pipe — creates standing water

- Dry well undersized — overflows during heavy rain

- Discharge onto neighbor's property

- Outlet blocked or buried