How to Install a Dry Well

We have a downspout that dumps rainwater onto our front walkway, which in winter turns into a sheet of ice. Is there a way to fix this problem?

—Tabby McCarthy, Olanthe, Kansas

Roger Cook replies: A wet walkway is not only a slipping hazard, it contributes to damaging frost heaves that can break apart pavement. If you can’t relocate the downspout, route the water under your walk and out to a dry well buried in your lawn.

What Is a Dry Well?

Roger Cook replies: This perforated, open-bottom plastic barrel, which sits in a hole and is surrounded by stones, captures water coming off your roof, and lets it slowly disperse into the ground. Your walkway will be drier, and your storm drains will be less overloaded.

To determine how many dry wells you’ll need, enter your roof area and soil type into the calculator at NDS, Inc. When you’re ready to start digging, follow the steps. After you’re done, fit your gutters with leaf guards so that the dry well won’t fill up with debris.

6 Steps to Installing a Dry Well

Step 1: Dig the Hole and Trench

Coming out from the downspout, at least 10 feet from the foundation (and 3 feet from any property line), dig a hole about 4 feet deep and wide. With a long-handled shovel, tunnel under the sidewalk and dig a trench 1 foot deep and 6 inches wide that slopes gradually toward the hole. Shovel the soil onto a tarp. Save the sod to patch over the hole.

Step 2: Line the Hole

Line the hole with landscape fabric cut from a 6-foot-long roll. The material prevents soil from clogging the stones around the dry well. Leave enough fabric outside the hole so that you can cover the stones once the dry well is installed.

Step 3: Set Up the Pipe

Buy enough 4-inch-diameter PVC pipe to reach from the end of the downspout to a point 14 to 16 inches into the hole. Also buy an elbow and a downspout adaptor (shown). Remove the existing elbow from the bottom of the downspout. Then, dry-fit the pieces and lay the pipe in the trench. Once you have a good fit, glue the pieces together with PVC cement.

Step 4: Check the Pitch

The pipe should slope toward the dry well ¼ inch per foot of run. A 2-foot level will show a ½ inch gap under one end when held level. Adjust the pitch by adding or removing soil under the pipe. When the pitch is set, attach the adaptor to the downspout using stainless-steel sheet-metal screws, then backfill around the pipe. Trim the opposite end if it’s too long.

Step 5: Install the Dry Well

Assemble the dry well, then use a hammer to knock out all the 1½-inch-diameter drainage holes and one of the 4½-inch ports. Shovel a 6-inch-deep layer of washed, ¾-inch rounded stone into the hole. Set the dry well in the hole and slide the port over the PVC pipe. Center the dry well and fill around it with stone until you reach its top edge.

Step 6: Fit the Overflow Emitter

Using a reciprocating saw, cut a 4-inch hole in the dry well’s lid and put the lid on. Take a length of 4-inch pipe and glue on an overflow emitter, which lets excess storm water escape. Trim the pipe so that the top of the emitter will sit at ground level when the pipe is glued to the lid. Cover the dry well with landscape fabric, and top it off with soil and sod.

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