Updated · Make This Useful
What is a French drain, and what should a drainage quote include?
A French drain is a gravel-filled trench with perforated pipe in the bottom, wrapped in filter fabric or a sock, that catches groundwater and surface water along its whole length and carries it downhill to an outlet. A solid drain pipe, the kind run from a downspout, only moves water from one end to the other. Ask the contractor to mark the route, depth and outlet on a sketch with the quote.
Where does a French drain go?
Across the path the water takes, on the uphill side of the wet spot, so it catches the water before it gets there: along the high edge of a soggy lawn, or beside a foundation wall that seeps. The outlet has to sit lower than the trench, where the water can spread out, run into a dry well, or reach a storm drain if the city allows it.
University of Minnesota Extension describes one set back from and parallel to the top of a bluff, catching water before it reaches the slope. A backyard works the same way: the trench goes where the water comes from, the outlet where it can leave without making a new wet spot, with rock around it so the discharge doesn't cut a gully.
Do I need a French drain or a downspout pipe?
Find the source first. Water off the roof belongs in a solid pipe from the downspout to an outlet away from the house; UMN uses non-perforated pipe wherever water only has to be carried. A French drain catches water moving through or across the ground, which a downspout pipe can't. Tie a downspout into a French drain and the roof water leaks back out through the perforations along the trench.
Watch the yard during a long rain before anyone digs. Water pouring off one roof corner points to the gutter and downspout. A soggy strip below a neighbor's slope points to a French drain. If you have both, ask for two separate lines, and send photos or a short video taken while it is raining.
Does a French drain fix a wet yard?
When water is moving toward the wet spot and there is somewhere lower to send it, yes. A low spot with nowhere downhill to drain needs regrading, a dry well or a pump; a French drain that ends in a flat yard just moves the puddle. Core aeration won't dry it out either: University of Maryland Extension says aeration alone can't solve soil saturation.
Ask where the outlet sits compared with the wettest point, and how much fall the pipe has along the route. If the plan needs a pump, get its power supply, discharge point and upkeep written into the quote. Then ask what you should see after the first heavy rain, and what the contractor will do if the spot stays wet.
What should a French drain quote list?
The route and length on a sketch, trench depth and width, the pipe (perforated, rigid or corrugated), the filter fabric or sock, the gravel, and the outlet with rock to stop erosion. Then the work around it: marking utilities before digging, hauling away the dug soil, and putting the lawn, beds or pavers back. Ask for a price per foot of trench too, so a route change gets priced on the spot.
Keep the final sketch with your house papers. Whoever digs the next fence post, plants a tree or runs an irrigation line needs to know where the pipe is.
Frequently asked questions
How deep should a French drain be?
Deep enough to catch the water you have. A shallow trench catches runoff across a lawn; catching groundwater before it reaches a basement wall takes a deeper one, and UMN notes that a deeper drain intercepts more groundwater. Get the depth and the fall to the outlet in writing.
Do French drains clog?
They silt up when soil washes into the gravel and pipe. The fabric wrap or sock is there to stop that, and UMN calls for wrapping the entire perforated length. Ask for a cleanout, so you can flush the pipe later.
Do I need a permit for a French drain?
Ask the city before the outlet empties into a street gutter or storm drain, and keep the discharge on your own property, away from the neighbor's lot. Ask the contractor who pulls any permit and whether it is in the price.
Sources
- University of Minnesota Extension: Stabilizing shoreland property · Checked
A French drain as a narrow trench of free-draining sand or gravel with perforated pipe wrapped in fabric or a filter sock; deeper drains intercept more groundwater; solid pipe and rock at the outlet.
- University of Maryland Extension: Maintaining an established lawn · Checked
Aeration relieves compaction but can't solve soil saturation.
Check what your quote includes
Keep the work, extras and total together. Prepare the questions you want answered before booking.
Check my quote