How to Install a French Drain, Step by Step

Quick answer: A French drain is a gravel-filled trench with a perforated pipe that collects groundwater and moves it away from your house. To install one: dig a trench with a 1% slope (1 inch of drop per 8–10 feet), line it with filter fabric, add gravel, lay perforated pipe holes-down, cover with more gravel, wrap the fabric over, and top with soil or stone. Expect $10–$50 per linear foot DIY, or $50–$100 installed.

When You Actually Need a French Drain

French drains solve water that arrives underground — soggy lawn zones, water pressing against a foundation, or a basement that seeps at the wall-floor joint. If your problem is roof water, fix gutters and downspout extensions first; that’s a $50 fix that solves half of all “drainage problems.”

“Half the French drains I’m asked to quote aren’t needed — the house just has downspouts dumping at the foundation. Extend those first. If the yard is still wet a week after rain, then we talk about digging.”

— Victor Salazar, Owner, Drylock Basement Systems

Step-by-Step Installation

• 1. Call 811 before digging — utility locating is free, and required.
• 2. Plan the run and outlet — water must exit somewhere legal and downhill: daylight on a slope, a dry well, or a storm drain where permitted. Never onto a neighbor’s lot.
• 3. Dig the trench — typically 12–18 inches wide, 18–24 inches deep, maintaining a consistent 1% slope. Check with a level on a straight board.
• 4. Line with non-woven filter fabric — leave enough overhang to wrap the top later. This is what keeps the drain from silting shut.
• 5. Bed with 2–3 inches of washed gravel — ¾-inch clean stone, never fines or pea gravel that compacts.
• 6. Lay perforated pipe, holes facing down — water enters from below as the trench fills. Rigid PVC outlasts flexible corrugated pipe.
• 7. Cover with gravel, wrap, and finish — gravel to within a few inches of grade, fold the fabric over, then topsoil and sod (or decorative stone for a visible drain).

Costs and Lifespan

Frequently Asked Questions

How deep should a French drain be?

18–24 inches for yard drainage; foundation drains run deeper, at footing level. Depth matters less than maintaining continuous slope to the outlet.

Do the pipe holes face up or down?

Down. Groundwater rises into the pipe from the gravel below — holes-up drains only capture water after the trench is already saturated.

Why do French drains fail?

Silt. Skipping filter fabric (or using cheap woven fabric) lets soil migrate into the gravel and clog the system within a few years.

Keep reading: the warning signs of foundation damage and what to check before finishing a basement.

The post How to Install a French Drain, Step by Step appeared first on House Logic.