By: Christopher Brooks
Although a quality sump pump is perhaps the single most vital component in a below-grade waterproofing system, it cannot do its job unless an efficient drainage system is in operation. Below-grade drainage systems vary with manufacturers and can offer different benefits.
The foundation supplies the base for your entire home and transmits the load of the structure to the supporting soil, according to Keith Reifke, national sales manager for Form-A-Drain, manufactured by CertainTeed Corp. (www.certainteed.com), based in Valley Forge, Penn.
"Because the foundation and basement are surrounded by soil, water can leak or seep into a home through cracks or holes, or through mortar between blocks," Reifke said. "The system functions as the footing form, perimeter drainage system, and radon evacuation system — where needed — all in one product."
This system represents an evolution in the way concrete footings are constructed. Unlike wood or metal forms, Form-A-Drain stays in place after the pour, eliminating the time and labor required to strip, clean and load forms, as well as install the drain tile.
"This not only reduces the labor cost on the job, but also creates an opportunity cost," Reifke said. "That is, the time saved by not having to strip forms and lay drain tile is time that can be devoted to another job. The system is manufactured to precise standards, eliminating the "crowning" common to forming lumber."
Alternative to pipe
Drainage performance makes Form-A-Drain a useful alternative to perforated pipe. "The lineals have one slotted wall that allows water to enter into the two channels and exit through installed drain outlets," Reifke said. "The drainage system is ideally located below the foundation wall and parallel to the footing — never below it. Level placement means high and low spots are eliminated, allowing improved water flow through the smooth interior surface of each lineal channel." Strong, rigid construction minimizes the possibility of failure due to a collapsed or crushed drain system. Because it forms a complete loop around the foundation, simple adaptation can help vent harmful radon gas.
Davis Carman, general manager of American Wick Drain Corp. in Monroe, N.C. (www.americanwick.com), said failure to provide proper drainage for an underground wall will always result in a build-up of hydrostatic pressure. American Wick Drain Corp. manufactures Amerdrain sheet drain and protection board, and Akwadrain strip drain.
"The load on an undrained wall is often double that on a properly drained wall. Without drainage, the wall would have to be built much stronger with the resultant increase in cost and weight," Carman said. "Hydrostatic pressure is the driving force for seepage of water through the wall into the interior of the structure. In addition, high hydrostatic pressure often shortens the life of waterproofing materials.
An undrained or poorly-drained basement wall and slab can result in a multitude of problems ranging from structural failure of the wall to damage to building contents from high humidity levels. Unprotected exterior waterproofing can be damaged, break down or even disintegrate over time. Damp walls can transmit interior heat into the surrounding soil.
"The installation of Amerdrain sheet drain adjacent to the wall and slab intercepts and collects ground water before it reaches the structure," Carman said. "The sheet drain reduces the hydrostatic pressure load on the walls and slab, which may permit a less expensive structure."
Sheet drain also acts as a protection board for waterproofing and helps to keep moisture from entering the basement, as well as reducing heat loss into the surrounding soil. Akwadrain strip drain is used at the bottom of the wall to carry water collected by the sheet drain for discharge to an outlet or sump.
Joseph Boccia, president of Boccia Bros. (www.bocciabros.com) in Long Island, N.Y. said the most effective, efficient method to eliminate basement flooding is draining the soil under and around the basement envelope. Boccia Bros. manufactures the Hollow Kick Molding system, a linear through floor drainage molding installed where the basement floor slab abuts the interior side of the foundation wall.
"This is achieved with a subfloor drainage system and a floating slab detail that conceals and protects the opening from the possibility of clogging and promotes the free flow of water," Boccia said. "No basement can be considered completely impervious to water seepage unless it has been protected. Thankfully, there are guaranteeable solutions to remedy a flooding basement and render it free of accumulation of water."
Basement seepage sources
Boccia said it's important first to consider the several sources that cause basement seepage:
- Cracks in the concrete floor slab and concrete foundation walls.
"Almost everyone who knows anything about concrete knows that it is subject to cracking for a number of reasons," Boccia said. "Walk along any sidewalk and note the lines in the concrete pavement. The lines are either control joints placed to control where the cracks may eventually occur or expansion joints, which are complete separations of the walkway and could be considered designed cracks."
- Cracks or debonded joints of block, brick or stone foundation walls.
"The mortar that is placed between the units the foundation wall may be constructed of and holding it together may eventually fail," he said. "There is a life expectancy to almost everything, including mortar. In addition, the same forces that create cracks in concrete acts on a masonry wall with similar results."
- Terminations of the floors and walls.
"Typically the basement would be constructed in three different units or pours," Boccia explained. "After the excavation, a concrete footing is installed. A separate foundation is then placed on top of the footing and a separate concrete floor is subsequently installed to complete the basement area. The result is a non-monolithic structure. At each junction between these three units or pours there is a separation. The most typical problematic separation is referred to as the cove, where the basement slab abuts the foundation walls."
- Penetration through the floors and walls.
"Lolly columns that pass through a basement floor slab and conduits that pass through foundation walls will result in a natural path for water seepage," he said. "A waterproof bond between the concrete or masonry and a dissimilar material will rarely exist."
- Porous concrete or masonry.
"Cement is not a waterproof material," Boccia declared. "Water may permeate the concrete or masonry barrier of the basement area via capillary action. It is possible that water could enter into the basement at any location, depending on the porosity of the cement and saturation of the exterior sub terrain."
- Below grade foundation sill plate or foundation windowsill.
"If the top of the foundation wall, commonly referred to as a sill plate is at an elevation that is below the elevation of the adjacent grade, water could flow over the top of the foundation wall during periods of flooding. If the basement windowsill is in a window or area well that accumulates water and creates a fish bowl effect, water will penetrate the window."
Hollow Kick Molding
According to Boccia, Hollow Kick Molding directs water through the floor and into the drain tile pipe, eliminating the possibility of water accumulating on the floor. "It also ensures proper air displacement, which will free the water flow through the sub slab piping. In simpler terms, it removes water at an elevation below the floor and foundation. Therefore, the basement does not become submersed in water and hydrostatic pressure is reduced."
Site requirements may necessitate the use of different drainage systems, depending on various factors such as water table and terrain. For your next job, check out the variety of drainage components that manufacturers offer. CH
Based in Bucks County, Penn., Christopher Brooks writes about the home for consumer and trade magazines.