French drain installation for Jersey City yards and side yards

A French drain is a gravel-filled trench with a perforated pipe at the bottom. Water in the soil follows the path of least resistance, and loose gravel is far easier to move through than packed clay or old fill. It seeps into the trench, drops into the pipe through its holes and runs by gravity to an outlet. The trench intercepts water before it reaches the place you don't want it, usually a foundation wall or a low patch of lawn.

This is outdoor work, and it's different from an interior drain system, which sits under the basement slab along the inside of the walls and feeds a sump. An exterior drain stops water out in the yard; an interior drain manages water that has already reached the foundation. Many wet basements need only one of them, and some need both. Our interior versus exterior guide lays out how we decide.

The two drains also behave differently in our soils. On the Palisades ridge, where rock sits close to the surface, water moves sideways along the rock and through the soil toward a foundation, so a trench on the uphill side of the house can catch much of it before it arrives. On low, filled ground near the Hudson, the water table itself is often the problem, and an exterior trench can only lower it so far. When that's the case, we tell you an interior system is probably the better spend.

Jersey City lots are small. A side yard between a frame house and its neighbor in the Heights or Greenville can be barely wider than the concrete walk that runs its length, with roof water pouring off both buildings into it. That narrow strip is often where a basement wall takes its worst soaking. A shallow French drain along the walk, or beneath it, catches that water and moves it to the front or rear instead of letting it pool against the house.

Rear yards behind rowhouses bring their own puzzles: fences, sheds, patios, old trees and almost no slope at all. We work by hand where machines won't fit, carry soil out through the side gate or the house, and protect floors along the way. In Bergen-Lafayette and other neighborhoods with rowhouses and two-family homes, a well-placed drain, sometimes paired with regrading the yard, turns a muddy yard into one you can use the week after a storm.

We cut the trench to a depth and slope set by where the water is and where the outlet sits, usually somewhere between knee and waist deep. The trench is lined with a non-woven filter fabric that lets water through but keeps fine soil out of the stone. Clean, washed gravel goes in the bottom, then the perforated pipe with its holes facing down, then more gravel, and finally the fabric is folded over the top before soil or stone goes back on.

That fabric wrap is what keeps a French drain working for many years. Without it, silt slowly fills the gaps between the stones and clogs the pipe, and the drain quietly stops draining. We also pitch the pipe evenly, with no dips where water and sediment can sit, and add a cleanout at the high end so the line can be flushed with a hose later on.

• Non-woven filter fabric wrapped around the whole trench
• Washed gravel above and below the pipe
• Rigid perforated pipe laid with the holes down
• Steady fall from the high end to the outlet
• A cleanout riser at the high end for flushing

A French drain is only as good as the place it empties. Water collected along the trench has to leave the property or go somewhere the ground can absorb it. On a sloped lot, the pipe can run out to daylight at a lower spot in the yard. On flat lots, which describes most of Jersey City, that's rarely possible, so we send the water to a dry well, a buried chamber that lets it soak into the ground slowly, or to a sump with a pump that lifts it out.

We won't build a drain that empties against a neighbor's wall or back toward your own foundation. Where the soil already holds water near the Hudson and Newark Bay, a dry well may fill and stay full, and a pumped outlet makes more sense there. We walk the yard with you, look at where your leader drains already run, and settle the outlet before any digging starts.