What a French Drain Actually Costs in Union County, and the Six Things That Move the Number

Nobody wants to ask what it costs. Everybody wants to know. So here is the honest version, with published figures you can check yourself and an explanation of why three quotes for the same yard can differ by a factor of four without any of them being dishonest.

We are not going to publish our own rates on a blog post. What a job costs depends on your ground, your access, your outlet and what is already buried out there, and a number pulled off a page you read in February is worse than no number at all. What this post will do is tell you what the published national ranges are, what moves a quote up and down, and how to tell a real number from a guess.

The published ranges

HomeGuide's cost research puts an exterior yard or curtain drain at $10 to $35 per linear foot, with typical installed yard drainage projects landing between $500 and $8,800. Interior basement perimeter systems run far higher, at $40 to $85 per linear foot and $4,000 to $17,000 installed. Crawl space systems sit between the two, roughly $2,000 to $8,000.

Those are national figures. They are a sanity check, not a quote. If somebody hands you a number well below the bottom of that range for a real excavated drain, something has been left out — and it is usually the outlet.

The six things that actually move the number

1. Length, and where the water has to go

Not the length of the wet patch. The length from where water collects to a place it can legally and physically leave. A twenty-foot wet spot at the bottom of a lot with no fall might need a hundred and forty feet of pipe to reach daylight. That single fact is the most common reason a quote surprises somebody.

2. Depth, and what the depth does to the spoil

Every extra inch of depth is more excavation, more stone, and more soil to take away. Excavated soil does not fit back in the hole it came out of — it swells by roughly a quarter — so a deep run generates a pile somebody has to load and haul.

3. Access

Whether a machine can reach the work changes the price more than almost anything else. A backyard behind a six-foot gate with a retaining wall on one side is a wheelbarrow job. The same trench in an open side yard is an afternoon with a mini excavator.

4. What is already buried

Irrigation lines, invisible fence, gas service, a septic field, the power feed to a shed somebody added in 2009. North Carolina law requires three full working days' notice to utility owners before digging, and the locate tells you about the utilities — it does not tell you about the irrigation the last landscaper installed without a drawing.

5. Restoration

The trench is the middle of the job, not the end. Sod, seed, straw, replacing a section of walkway, resetting a bed. On a finished lawn, restoration is often a bigger line than the pipe.

6. The outlet

If there is a low point on your property where water can daylight, the job is straightforward. If there is not, you are into a pumped system, a dry well, or a negotiation with a neighbour, and all three cost real money. Ask every contractor where the water is going to come out, and go look at that spot with them. If nobody can show you the outlet, nobody has designed the job.

Why three quotes disagree

Most of the time it is because they are not quoting the same job. One is a surface swale, one is a perforated pipe in stone, one includes a catch basin at the downspouts and a solid line to daylight. They look similar on paper and they are different pieces of work with different lifespans.

Ask each one, in writing:

• How many linear feet, and of what — perforated or solid?

• What stone, what size, and is it wrapped in geotextile?

• Where does it outlet, and what is the fall from inlet to outlet?

• What happens to the spoil?

• What restoration is included?

• What is the warranty, and what voids it?

Six answers turn three incomparable numbers into three comparable ones. If you want the full version of that exercise, the Drainage Estimating and Materials Takeoff is a blank worksheet for the whole takeoff — it has no prices in it, deliberately, because the figures are yours and your market's.

The number nobody quotes

Here is the arithmetic that should frame the whole decision. One inch of rain on a square foot of roof produces about 0.623 gallons. A 2,000 square foot roof in an ordinary one-inch rain sheds roughly 1,247 gallons. Divided between four downspouts, that is about 312 gallons out of each one — five bathtubs, delivered in an hour, a few feet from your foundation.

Against that, the cheapest fix in home ownership is a downspout extension. Before you price a drain, price the thing upstream of it. We have watched a great many expensive proposals become unnecessary because somebody moved water twelve feet further from the house for the cost of a length of pipe.

If this is your yard

Water in the same place after every rain is a solved problem, and the first visit is about finding your outlet, not selling you pipe. We work in Waxhaw, Weddington, Marvin, Wesley Chapel, Indian Trail, Matthews, Monroe, Mint Hill, Stallings and south Charlotte. Call 980-280-7638 or use the drainage page to ask for a look.

Every guide we have written is sorted by symptom on the Start Here page.

Who wrote this. Alex Purdy owns Carolina Terrain LLC in Waxhaw and holds North Carolina Landscape Contractor Licence CL.1872, the NCSU Stormwater Control Measure Inspection and Maintenance Certification (#5970), and NDS Certified Drainage Contractor status. He is not a Professional Engineer and not a Registered Landscape Architect. Nothing here is an engineered design, a legal opinion, or a substitute for either.

Sources

• HomeGuide, French drain cost research — published ranges for exterior, interior and crawl space systems, and the material and labour components behind them

• North Carolina 811 — three full working days' notice to utility owners before digging

• Roof runoff arithmetic — 0.623 gallons per square foot per inch of rainfall; the rest is multiplication you can repeat

Rules and published figures change. Everything here was checked when this was written. Before you rely on any of it for a permit, a purchase or a build, confirm it with the agency that issues it.