How to Compare Three Drainage Quotes That Do Not Match

You asked three contractors for a price on the same wet back yard. One came back at a figure, one came back at roughly double, and one came back at four times the first. Nobody is necessarily lying. In our experience they are usually quoting three different jobs, and the quotes do not say so anywhere.

This is not a list of questions to ask on site — we have written that one already. This is about the piece of paper afterwards, and how to lay three of them side by side so the comparison means something.

Why the numbers diverge

Five things account for nearly all of it.

• Different systems. A surface swale, a perforated pipe in stone, and a full catch-basin system with solid line to daylight are three different pieces of work with three different lifespans. On paper they can all read as "install drainage".

• Different lengths. One has priced to the edge of the wet patch. One has priced to an actual outlet a hundred feet further on. The second is the real number.

• Restoration included, or not. Sod, seed, straw, resetting a walk. On a finished lawn this is frequently a bigger line than the pipe.

• Spoil handling. Excavated soil swells by roughly a quarter and does not go back in the hole. Somebody has to load and take it away, or it becomes a new mound in your garden.

• Risk priced in, or left out. Rock, an unknown buried line, a wet-weather delay. Some contractors carry it, some will come back with a change order.

The normalising table

Copy this onto one page and fill a column per quote. Most of the confusion resolves itself once the three are on the same grid.

• System type — swale, perforated in stone, solid line, catch basins, or a combination

• Total linear feet — and of what diameter

• Perforated or solid — and where it changes from one to the other

• Stone — size, washed or not, quantity if stated

• Geotextile — included, and what type

• Number of inlets or basins

• Named outlet — where exactly does the water come out

• Fall from inlet to outlet — stated as a measurement or a percentage

• Spoil — hauled away, or spread on site, and where

• Restoration — sod, seed, straw, hardscape repair

• 811 locate — who calls it and when

• Permits — who is responsible for establishing whether any are needed

• Warranty — duration, and what voids it

• Exclusions — read this line twice

• Payment schedule

Any row you cannot fill from the written quote is a question to send back by email. The answers arriving in writing are worth more than the answers on the phone.

What a good quote looks like in writing

It does not have to be long. It has to be specific. A quote we would be comfortable receiving ourselves names the system, gives lengths and materials, names where the water comes out, and says what is excluded.

Two sentences that tell you somebody has actually walked the job:

• A named outlet, with its location described rather than implied.

• A stated fall or slope, rather than "runs downhill".

Two sentences that tell you they have not:

• "Install French drain in rear yard" with a single number and nothing else.

• Any quote with no exclusions at all. Every real job has them.

The five things worth checking on any quote

1. Does the length make sense against the outlet?

Measure roughly from the wet area to wherever the quote says the water will discharge. If the stated footage is far shorter than that distance, the pipe is ending somewhere the paper does not mention.

2. Is there a stated fall?

One percent is the practical minimum for a solid drain line and it is unforgiving of sloppy work. Two percent is the target. Over fifty feet, two percent is twelve inches of drop; over a hundred feet, twenty-four. A quote with a number here is from somebody who brought a level.

3. Is the geotextile specified?

A non-woven needle-punched fabric wrapping the stone is what stops soil migrating in from the sides and below. Without it, a functioning drain becomes a muddy trench full of rock in about four or five years. If fabric is absent from all three quotes, ask all three why.

4. Where does the spoil go?

A hundred feet of trench a foot wide and eighteen inches deep produces something close to seven cubic yards of loose soil. "We will spread it out back" means a new low spot is being created somewhere. Ask where.

5. What is excluded?

Rock excavation, irrigation repair, unknown buried utilities, hardscape repair, permits, wet-weather delays. Exclusions are not a red flag; a contractor who has thought about the job knows what could go wrong. Silence on all of it is the red flag.

The comparison that actually matters

Once the three are normalised, the question is rarely "which is cheapest". It is which of these three has been designed, and which two have been guessed. A designed job has an outlet you can walk to, a fall somebody measured, and a materials list that follows from those two facts.

If exactly one quote has those things and it is the most expensive, you have not found the expensive quote. You have found the only real one, and the other two will cost more in the end because the work will be done twice.

If none of the three has them, none of them has designed the job, and the cheapest is as good a bet as any — which is a genuinely reasonable conclusion to reach, as long as you reach it knowingly.

One more thing worth asking

Ask each of them what they would do if the answer were a downspout extension and an afternoon of regrading. A great many wet yards in this county are fixed for a fraction of what a trench costs, because the water was being delivered to the wrong place by the roof rather than arriving through the ground.

The contractor who tells you that, and loses the bigger job by saying it, is the one to hire for the job you actually need.

If you want the underlying arithmetic — stone volumes, fabric widths, spoil with swell, fall over run — the Drainage Estimating and Materials Takeoff is the blank takeoff sheet, with no prices in it. The figures are yours and your market's; the method is what makes three quotes comparable.

If this is your yard

If you are holding three quotes that do not agree, we are happy to be the one that names the outlet and states the fall. 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

• Trade practice on fall — 1 percent practical minimum and 2 percent target for solid drain lines; the drop is run length times 12 times the percentage

• Spoil swell — excavated soil commonly swells about 25 percent; volume is trench cross-section times length times 1.25

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

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.