project-guides · 6 min read
French Drain Guide
Everything you need to design, size, and install a residential French drain.
A French drain is a perforated pipe wrapped in washed rock and filter fabric. It collects subsurface water and carries it to daylight or a collection point.
The stack, top to bottom
- Soil or sod cap (optional).
- Filter fabric folded over the top.
- 3/4" washed drain rock backfill.
- 4" perforated pipe, perforations down, sloped 1% minimum.
- 3"–4" bed of drain rock.
- Filter fabric lining the trench.
Warning
Skipping the filter fabric is the single most common failure mode. Silt migrates into the rock and stops the drain within a couple of seasons.
Frequently asked questions
- How deep should the trench be?
- 12"–24" deep is the residential range. Deeper if you're intercepting a specific saturated layer.
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