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Drywells Help Keep Basements Dry

House Doctor | Gary Dymski

May 18, 2000

YOU SHOULDN'T HAVE to worry about water in your basement every time there's a heavy rain. And you might not have to break the savings account to keep your basement dry.

It won't be easy, but if you have a strong back for some minor excavating, there's a good chance you'll be able to employ a couple of effective "waterproof" techniques that could keep household items from floating in the basement after a heavy rain.

The success of each application -- building a drywell for your gutter downspouts and creating a proper grade for your foundation -- relies on your already having a sound roofing system, including gutters and downspouts, and a basement free from cracked walls and floors. Your roofing system is important because it's designed to divert rainwater away from the house; a system with dried shingles, rotted wood and sagging gutters isn't likely to do its part in keeping your basement dry.

Before there's a repeat of last month's heavy rainfall, visually inspect your roofing system. If it appears sound-that also means no worn shingles-consider one of the following methods of waterproofing.

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Building a drywell. This sounds more difficult than it really is. A drywell is a temporary underground storage area for excess water as it percolates into the earth, and this one will be for rainwater from one or more downspouts. You can build your drywell the old-fashioned way, digging a hole and stacking cinderblocks or cesspool stones in a circular fashion. However, the best method for a do-it-yourselfer is to purchase a specially designed plastic chamber for stormwater drainage. The smaller of these plastic chambers (there are three sizes) can hold about 122 gallons (more than 16 cubic feet) of water.

Among the manufacturers of plastic chambers for stormwater drainage and septic tanks are Infiltrator Systems Inc., in Old Saybrook, Conn. (888-335- 3884; www.infiltratorsystems.com); and Cultec Inc. in Brookfield, Conn. (203-775-4416; www.cultec.com).

"Plastic drywells are lightweight and much easier to use than the alternatives," says Hank Carlson, owner of Andrew Carlson & Sons Inc., a maker of precast concrete products in Kings Park.

Carlson sells both plastic drywells and the more conventional precast concrete drywells. The small concrete drywells for residential use are 2 feet high and come 4 feet, 6 feet and 8 feet in diameter. Carlson says heavy construction equipment is needed to set a precast concrete drywell in place, and it's backbreaking work to stack cesspool blocks. One or two persons can carry and set the plastic chambers in place, Carlson says, and the price is right, too; about $100 for the 122-gallon chamber.

No matter which method you choose, using plastic or building a drywell out of stone, you'll have to bury the drywell in your yard, probably at least 10 feet away from your foundation and in a reasonably straight path from the downspout.

Try using one plastic chamber for a problem downspout, and if the drainage doesn't improve, you can double the capacity by adding another chamber. (The chambers can be connected with end caps and drainage pipe.)

If you build your drywell with blocks, a well size of 6-foot or 8-foot diameter is the wiser choice. This should be large enough to handle the stormwater from the roof of a small home. Cesspool blocks are 8 inches high, 4 inches wide and 16 inches high and heavy; get some help when stacking them. Also, stagger the blocks when stacking so the top stone falls in the middle of the two stones beneath it, sort of in a herringbone pattern.

The outside walls and bottom of the drywell, plastic or stone, must be surrounded by crushed rock or gravel, so dig your hole at least a foot or two wider than the diameter of the well. (In the case of installing a plastic chamber, follow all manufacturer's instructions.)

It's also necessary for the drainage pipe, which links the downspout to the drywell, to lie on a bed of crushed rock.

Once the well is in place, you can assemble your drainage pipe. Use 4- inch solid polyethylene drainage pipe, which is specifically designed for such jobs. It's available at most home centers in 10-foot lengths and is easily cut with a hacksaw. Pieces are snapped or glued together and fit snugly into elbows and couplings. Design the run so the drainage pipe reaches the downspout slightly above the ground. Finish the run at the foundation with a downspout adaptor, which is made to connect the downspout to the pipe.

Be sure to fit all drainage pipe couplings and elbows together before gluing.

In the case of a stone drywell, use a piece of slate covered with roofing paper as a lid, then cover with soil and relandscape the area. You also should know the location of the drywell in case there are problems or if you sell the house.

Improving the foundation grade. The ground around your house should slope slightly away from the foundation and be free from pockets where surface puddles can form.

If you have a basement wall, however, that seems to be leaking, lining the grade outside the house with plastic sheeting and landscape rock can help divert water away from the wall.

Again, you'll need to do some digging. Clear an 8-foot-wide area along the length of the problem exterior wall. Dig just a few inches deep and line with a sand bottom. Grade the sand so it slopes away from the foundation, then line the area with sheets of 6-mil black plastic. The plastic should start about 2 inches above the foundation wall. (Rolls of plastic sheeting are available at home centers and nurseries.)

Cover the plastic lining with a 2- to 4-inch layer of the crushed rock. This combination of plastic sheeting and rock will send rainwater to drain farther away from the foundation.

Because the finished area should slope a minimum of 6 inches at 10 feet from the foundation, the amount of sand and rock you use will vary. You probably won't want this rocky display in your yard, so you can cover it with more sand, soil and sod. This final layer of soil and sod should hide the plastic that was exposed along the foundation.

Before covering the area, wait through a couple of heavy rains to see if the basement area stays dry.