How to Build a Dry Well for Yard Drainage That Works

Your downspout dumps 1,500 gallons onto the same patch of lawn during a one inch storm, and that patch stays soggy for three days while the basement wall next to it weeps. A dry well for yard drainage can take that water underground and let it soak away slowly, but only if the soil can actually absorb it. Get that part wrong and you have buried a very expensive bucket.

I have designed drainage for residential lots for fourteen years, and dry wells are one of the tools I recommend least often and most carefully. Here is how to decide whether one fits your site, how to size it, and how to install it so it still works in ten years.

What a dry well for yard drainage actually does

A dry well is an underground chamber or pit filled with stone that collects runoff from a downspout, a driveway or a low spot, then lets it seep into the surrounding soil over hours. It does not make water disappear. It stores a storm's worth of water temporarily and gives the ground time to take it.

Common forms are a plastic chamber with perforated sides, about 50 gallons each and around $80 to $150 at supply yards, or a gravel-filled pit wrapped in filter fabric. Both work. Chambers hold more water per cubic foot because they are mostly empty space, while a gravel pit holds roughly 30 to 40 percent of its volume as water.

Test your soil before you dig anything

This is the step most homeowners skip, and it decides everything. A dry well in heavy clay will fill during the first storm and stay full for a week.

1. Dig a hole 12 inches wide to the depth where the bottom of the dry well will sit, usually 3 to 4 feet.
2. Fill it with water and let it drain completely to saturate the surrounding soil.
3. Fill it again to 12 inches deep and measure the drop every hour for four hours.

Also check your water table. If you hit standing water in the test hole during a wet season, a dry well has nowhere to drain. It needs at least 2 feet of unsaturated soil below its base.

How to size a dry well

Start with the roof or paved area draining to it. One inch of rain on 1,000 square feet produces about 623 gallons. For a 1,200 square foot roof section, a one inch storm sends roughly 750 gallons to the downspout.

Many local codes ask you to hold the first inch, or a 10 year storm, whichever is set by your jurisdiction. If you have no requirement, design for one inch as a sensible minimum.

Now convert. A gravel pit stores about 2.5 gallons per cubic foot with 33 percent voids. To hold 750 gallons you need about 300 cubic feet of stone, which is a pit roughly 8 by 8 by 4.7 feet. That is a lot of digging. Plastic chambers shrink this: fifteen 50 gallon units hold the same volume in a far smaller hole.

In soil that drains 1 to 4 inches per hour, the well empties between storms and you can size closer to the minimum. In marginal soil, add 50 percent and plan an overflow.

Installing a dry well step by step

1. Call before you dig. Mark utilities first; our guide to calling 811 and reading the utility flags explains the wait times and paint colors.
2. Locate it at least 10 feet from the foundation and downhill from it, 10 feet from property lines, and well clear of septic fields and wells. Check local setbacks, which can be larger.
3. Excavate to the tested depth. Keep the bottom level and do not compact it; you want it open and absorbent.
4. Line the sides and top with non-woven geotextile fabric. Leave the bottom unlined in most soils so fines do not clog a membrane exactly where water needs to exit.
5. Set the chamber or fill with 1.5 to 2 inch clean washed stone. Never use crusher run, which packs solid.
6. Run 4 inch solid pipe from the downspout at a slope of at least 1/8 inch per foot, ideally 1/4 inch.
7. Add a pop-up emitter or overflow at the surface so that when the well is full, water exits onto lawn away from the house instead of backing up the pipe.
8. Cap with fabric and 8 to 12 inches of soil, then seed or sod.

Put a leaf filter or a cleanout at the downspout. Shingle grit and leaves are the main reason dry wells clog within five years. A $25 inline filter basket is far cheaper than digging the whole well back up.

Why a dry well is often not the first fix

Online, a dry well is presented as the default answer to a soggy yard. I push back on that. In most of the wet yards I visit, the real problem is grading. The soil around the house slopes toward it, or a low spot was created when the lot was built. Burying a chamber does not change any of that, and surface water from the neighbor's lawn still flows into the same spot.

The cheaper, longer lasting fix is usually to restore a slope of 6 inches over the first 10 feet away from the foundation and extend the downspout. We explain that in grading a lot so water moves away from the foundation. A dry well is a good second layer when you have a concentrated source, like a large roof valley, and decent soil.

It is also not a substitute for a French drain when groundwater is the issue. If water is seeping up rather than flowing on top, read why French drains fail within two years before choosing either.

Frequently asked questions

How deep should a dry well be?

Most residential dry wells are 3 to 5 feet deep, depending on volume needed and soil. The base should sit at least 2 feet above the seasonal high water table. Deeper is not better if it pushes the bottom into wet or clay layers.

How long does a dry well last?

A well-built dry well with a leaf filter and fabric-wrapped sides usually works for 20 to 30 years. Without a filter, sediment can clog it in 5 to 10 years. Open the cleanout every spring and flush out debris.

Do I need a permit for a dry well?

It depends on your town. Many jurisdictions regulate dry wells as underground injection or stormwater features, especially if they take driveway runoff. Check with the local building or stormwater office before you dig.