Laying the foundation for a dry basement

Inspector's Eye

Waterproof with piping, sump pumps, but also find cause of water

March 24, 2002|By Dean Uhler

A letter from Edwin Leimkuhler of Baltimore described an offer from a waterproofing contractor to install a black, slitted, corrugated plastic tubing around the perimeter of his basement.

He was told, however, there was a danger of it becoming clogged with an accumulation of dust and dirt. Another company proposed using rigid plastic pipe with holes in the underside of the pipe. He wants to know whether there is any important difference.

What Edwin is describing is the essential component of a typical basement waterproofing system - a drain tile or "French drain."

The potential for clogging by dust, dirt and, primarily, fines - very small soil particles - is a major consideration with a drain tile. However, the choice of pipe, corrugated or rigid smooth-wall, is probably not critical - the pipe just has to be perforated, to allow water into it, and strong enough to prevent collapse.

What is of utmost importance to prevent clogging is the manner in which the pipe is installed. To prevent fines from entering and clogging the pipe, it should be installed in a bed of graded stone (pea gravel or crushed rock) and surrounded by a layer of filter fabric.

The interstices between the stones will provide multiple paths for water to flow into the drain pipe, and the filter fabric will prevent fines from washing into the pipe. The fabric can be placed around the entire bed and can be installed as a sleeve around the pipe as well. The placement of filter fabric around the bed should be considered essential; without it, the soil surrounding the bed of stones can easily ooze into and clog the spaces between the stones.

Kathy Crosby of West Baltimore asked about waterproofing proposals for the basement of her mother's townhouse.

The basement has developed a water problem in the past year, which she said is ruining the brick foundation wall. Kathy has checked the rain gutters and found no obvious defect. One contractor who looked at the problem said the water is probably coming in because the foundation is worn where the neighbor's downspout used to discharge water next to it (until Kathy fixed it last year).

The contractor proposed fixing the foundation with concrete or installing a sump pump system for $1,900. A waterproofing company proposed putting in a sump pump system for $2,700. Kathy is asking whether these proposals make sense.

The estimates for a waterproofing system (sump pump and French drain) are not excessive, but it is also important to make sure that drainage problems at the exterior of the house, which may be the underlying cause of a wet basement, have been identified and corrected.

Waterproofing systems are an imperfect solution - they keep the water off the floor, but often don't stop it from causing other problems, including possible foundation damage. And since drainage problems at the foundation exterior are often the underlying cause when a water problem develops in a formerly dry basement, it is entirely possible that correcting them could succeed in drying out the basement without incurring the expense of a waterproofing system.

Kathy's repair of the neighbor's downspout by installing an extension was an important repair. Other possible sources of water that should be corrected include paved walkways or patios that have settled or broken. A pavement that has settled at the edge nearest the house may drain large volumes of water toward the house's foundation. Or a cracked pavement may allow water runoff to infiltrate the ground close to the foundation.

Pavements with either condition should be repaired or replaced. Similarly, depressions in the soil surface within a few feet of the house can cause runoff to pond and soak into the ground near the foundation. Dense topsoil should be added as needed to create a slight down slope from the house extending at least three feet out.

Fixing the foundation, as proposed by one of the contractors Kathy consulted, may be helpful but is unlikely to be a complete solution. The foundation wall was probably never truly waterproof and repairing the concrete won't make it so - unless, in addition, a drain system is installed at the foundation exterior - a very major undertaking.

Inspector's Eye

Dean Uhler has been a home inspector for more than 12 years and is president of Baltimore-based Boswell Building Surveys Inc. Uhler is a member of the American Society of Home Inspectors (ASHI) and is the treasurer of the Greater Baltimore Chapter of ASHI.

Questions, with name, address and daytime telephone number, about homes and home inspections can be faxed to 410-783-2517, e-mailed to or mailed to Inspector's Eye, Second Floor, 501 N. Calvert St., Baltimore, Md. 21278-0001.

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