Everything You Need to Know About Basement Waterproofing
Use gutters, a drainage system, and interior waterproofing to keep your basement dry
Heavy rain and melted snow runoff can come in through cracks or leaks in the foundation, where it can warp floorboards, rust appliances, and turn finished rooms into mildewed messes. Fortunately, regrading or rerouting can correct most drainage problems.
Outdoor Waterproofing Basics
To prevent water from leaking through your foundation, gutters are your first line of defense. While gutter-and-downspout systems protect your house from precipitation, they can also compound drainage problems by concentrating roof runoff at a house's corners, close to the foundation. When clogged gutters overflow, water can pool around your foundation. So be sure to remove any leaves and debris left over from winter, then install leaf guards to keep them clear.
To carry water away, attach a sloped leader to each gutter and guide water at least 10 feet from the foundation. Alternatively, downspouts can dump directly into an above- or underground catch basin. In that case, runoff should be carried through a solid drainpipe to a dry well—an in-ground perforated tank that collects water and lets it seep into the ground. High-impact plastic dry wells are easy to handle and work efficiently on small drainage problems. Larger pre-cast concrete drywells require machinery for their installation but will handle larger volumes of water.
Houses without gutters often have problems caused by water splashing against the foundation. In this case, a collection system should be installed at the roof's drip line. Dig a V-shaped trench, line it with thick plastic and lay in a perforated pipe, pitched toward a drywell or outlet pipe. Then cover the pipe with landscape fabric to keep out dirt and fill the trench with stones to allow water to leach through topsoil and into the pipe.
Regrading the ground closest to your foundation can also help. Clear away plantings and gently build up the soil to slope away from the foundation. The 10 feet of ground closest to the house should slope at least six inches downward at an incline of at least ¼ inch per foot to keep water from draining improperly. Simply add soil, raking it smooth, until the grade is highest at the house's perimeter.
Drainage System Options
There are two types of drainage systems, surface and subsurface. Surface drainage works well for clay-based soils, while subsurface drainage is generally best suited to soils of high sand or silt content. The typical surface system consists of swales—shallow open trenches—leading to one or more dry wells that empty into a deep runoff trench dug in the lowest corner of the yard. Open trenches are the most effective way to intercept and carry away excess water puddling on the ground's surface.
Subsurface drainage systems consist of several French drains that carry off water from poorly drained areas through collection pipes linked to a deep runoff trench dug in the lowest corner of the yard. Ideal places to put French drains are the bases of slopes, along retaining walls, or any other area where water tends to collect.
To build a French drain, dig a sloped 3-foot-deep trench to carry water away from the area to be drained. Line the trench with landscape fabric to keep surrounding soil out and keep the gravel porous so that water flows easily. Then, install a 4- or 6-inch perforated drain line at the bottom of the trench, and backfill it with 4 inches of gravel. Cover it with drainage-friendly topsoil. Your entire system of drainpipes should connect to a 6-inch solid collection pipe that goes all the way down to the runoff trench.
Interior Waterproofing Measures
There are several steps to internal waterproofing, the first of which involves sealing cracks and holes in the concrete walls of your foundation with hydraulic cement. The cement will expand inside the fissures and create a water-tight seal. Then, apply a coat of waterproof masonry cement to your basement walls. This will seal the pores of the concrete and stop moisture from seeping through. These efforts combined with proper above-ground drainage will do a lot to prevent moisture from coming through the walls.
Sump pumps equipped with a battery-backup system will continue to run even if the electricity goes out during heavy flooding. The rechargeable battery will operate for 7 to 10 hours before recharging is necessary. The batteries should be replaced every 2 years. Alternatively, water-powered sump pumps rely on water pressure, not a rechargeable battery, to keep pumping during a blackout.
A water-powered sump pump will run virtually forever, as long as there's water pressure. However, this system is only suitable for homes connected to a municipal water supply, not a well pump. Another complementary internal drain system is the French drain. However, installation of this drain type will require a professional installation and may be costly.
Taking It One Step Further
Other tips include labeling the water main shutoff valve so everyone in the family knows how to find and close it in case of an emergency. Also, ensure that your appliances like a washing machine, are draining into the appropriate drains. Additionally, installing a water leak detector is useful for alerting you that there's a leak. Whole-house leak detectors use wireless transmitters that detect and then automatically shut off the water in the event of a leak. Or, try a programmable auto-shutoff leak detector that’s designed to measure the amount of water continuously flowing, and will turn off the flow at a set interval.