Installing a dry well
First off, even if you have a tough drainage
problem, use a dry well only as a last resort. Ideally the
ground around your home should slope between 1/2
and 1 in. per foot away from the foundation for at least
the first 6 ft. If you don't have this much slope, the standard
3-ft. extensions for downspouts probably won't do much
good. Water from a severe storm can really add up fast—a
1,000-sq.-ft. roof will shed about 620 gallons of water during
a 1-in. rain, or about 103 gallons per downspout if you have
six downspouts. That's a lot of water dumped right next to the
First, try longer (6-ft.) downspout extensions. Make them
removable so you can move them when you mow your lawn.
The next best solution is to install an underground drain
using plastic drainage pipe. Basically, it's the drainage pipe
portion of the illustration that runs at a downward
slope until it reaches daylight, rather than the dry well. The only
catch with this system on a flat lot is whether you actually
have a low area where the drainage pipe can come out. And,
of course, it takes a lot of digging!
As a last resort, consider running the underground pipe to
a dry well that's at least 20 ft. from the foundation. This
will hold much of the water until it can naturally seep into the
Keep in mind the limitations of a dry well. You probably
can't size it large enough to hold more than a portion of a
heavy rainfall. If your subsoil is heavy clay, drainage will be
slow. And once the dry well fills, the water will fill up the
drainage trench back toward the house and potentially cause
more leakage. An overflow tube added to the dry well (not
shown) or a slotted grate on the catch basin will help
relieve this problem.
To begin, find the downspout nearest the spot where water
enters your basement and install a 6-ft.downspout extension
and elbow. Center a small catch basin
at that spot. Then mark the dry well location and
drainage pipe path and dig the trench and dry well hole.
Make the trench about 12 in. wide to contain the 4-in. pipe plus 3 to 4 in. of surrounding crushed
rock (1-1/2 to 2 in. diameter). Slope the trench downhill at
least 1-1/2 in. every 10 ft. Make the dry well hole about 8 in.
wider in diameter than the plastic well to allow space for at
least 3 to 4 in. of crushed rock.
We purchased a sump liner with heavy-duty lid for our
dry well. Before installing it, remove the cutout for the 4-in.
tubing and drill 1-in. holes every 8 to 12 in. so water will
escape and percolate into the surrounding soil profile. Wrap
landscape fabric completely around the sump liner and pull
a fabric sock over the tubing to keep out silt (both products
are available at home centers).
Finally, install all components and backfill with rock. Close
the holes and trench with dirt. Don't forget to use screens on
your gutters and a screen inside the catch basin to keep leaves
and debris out of the tubing and dry well.