French Drains

A French drain is a trench filled with gravel and a perforated pipe that collects water moving through the soil and channels it to a lower point away from your home. Installed around a foundation, it's one of the most effective and affordable ways to prevent water from reaching your basement or crawl space in the first place.

When You Need One

Flooding and foundation moisture problems are often the result of sloped ground directing water toward your home rather than away from it. If your property sits downhill from a neighbor's lot, heavy rain can send groundwater rushing onto your property. When the soil can't absorb it fast enough — which is common with the Triangle's clay-heavy soil — that water pools against foundation walls and eventually finds its way into a crawl space or basement. A properly installed French drain catches that water at the source and carries it to a safe discharge point before it becomes a problem indoors.

How a French Drain Is Built

The parts are simple and the details are what decide whether it still works in ten years:

• Slope. The trench falls continuously toward the discharge point. A drain that runs flat, or dips somewhere along its length, holds water instead of moving it and silts up from the low spot outward.
• Filter fabric. Wrapped around the gravel so fine soil cannot migrate in. Its absence is the single most common reason a drain that worked for two seasons stops working in the third.
• Washed stone, not fill. Clean angular gravel keeps the voids open. Cheaper unwashed material carries the fines that clog the pipe.
• Perforated pipe, holes down. Counter-intuitive to most people, and correct: water rises into the pipe from the gravel bed below rather than falling into it from above.
• A discharge point that actually discharges. Daylight on a downslope, a dry well, or a sump pit. Ending a drain somewhere the water has nowhere to go relocates the puddle rather than removing it.

Yard Drainage vs. Foundation Drainage

These get conflated and they solve different problems. Yard drains catch surface water — the low corner that stays soft for days, the patch of lawn that will not grow, runoff arriving from a neighbouring lot. Foundation drainage deals with water moving through the soil against your foundation walls, which is what ends up in the crawl space.

A property can need one, the other, or both, and the inspection is largely about telling them apart. Putting a yard drain in the low spot does nothing for a foundation taking on groundwater, and a footing drain does nothing for a lawn that will not drain.

French Drain Repair

Drains fail quietly. The symptom is usually that water is back where it used to be, and the cause is almost always one of a short list: silt has filled the gravel bed because there was no filter fabric, roots have found the pipe and grown into it, the pipe has been crushed by traffic or settlement, or the discharge end has been buried, blocked, or landscaped over.

Whether that is a cleaning, a section replacement, or a rebuild depends on which of those it is. It is worth diagnosing rather than assuming — a blocked outlet is an afternoon, and a bed full of fines is a new drain.

French Drain Services

• Yard drains — an economical way to prevent moisture problems before they start, catching surface water in low-lying areas of your yard
• Drain extensions — keep water from pooling against foundation walls and entering the crawl space by extending drainage further from the home
• Crawl space drains — installed alongside a sump pump to ensure water inside the crawl space is directed to a catch basin and pumped out
• Repair and replacement of existing drains that have silted, crushed, or lost their outlet

French drains are frequently paired with a sump pump so that any water the drain collects has somewhere to go — the drain does the collecting, the pump does the removing. Where the water is already under the house, that pairing plus encapsulation once the space is dry is the complete answer rather than any one of the three.