In most places where underground water is a concern, foundation footing drains are mandated. If footing drains are placed correctly, groundwater will not collect outside the basement walls, protecting the interior space from flooding. We’ll talk about both brand-new and updated bases. In new construction with a complete basement, the walls below grade must be coated with waterproofing to prevent water from seeping in. Concrete masonry unit foundations also need a coat of cement plaster before waterproofing can be applied. A “cant” is built using mortar or a prefabricated fiber material at the external footing of the foundation wall. A cant, typically a triangle, directs water away from the foundation wall and into the footing drains.
For the footing drain to reach daylight, the excavator hired by the contractor must dig a “tail” ditch from a foundation corner to a level lower than the footing. This could be a few feet or a hundred or more. Water can easily flow down the tail ditch because of its downward slope. The excavator will now spread a layer of three-quarter inch gravel around the perimeter of the foundation, a distance of about twelve inches. After being leveled by hand, the stone should sit about five inches lower than the finishing height of the internal basement floor. This gravel does not require compacting. The contractor then runs a closed circuit of four-inch PVC pipe along the edge of the concrete footings, connecting 90-degree elbows where needed to reach the corner of the tail ditch. There, a Tee fitting is installed so that pipes coming from opposite directions can be linked, and a third pipe can escape the tail ditch through the space left. The PVC pipe used to enclose the footing features two parallel sets of holes. When finished, these holes should be pointing down. Do not listen to those who advise you to expose the holes so water can “fall into” them. As a result, the pipe quickly became clogged with sand, silt, and dirt that washed down from above. When water accumulates around a building’s base, it will see the pipe’s holes on the ground and enter. Since water always finds the lowest place, drainage pipes should be built so that water flows downhill. Thanks to the tail ditch, water can still drain to the daylight end of the footing drain pipes, even if it is not perfectly level. It’s the easiest way to get what you want. If water has a line to follow, it won’t have to force its way through a porous foundation wall or floor.
After the pipes have been laid, they are covered with another four or five inches of gravel. Once the pipe is finished, it is hidden from view. After the gravel job is done, a protective layer is laid on top using felt paper, hay, or red rosin paper to keep the dirt out as much as possible. PVC piping with no perforations is used for the tail ditch. Perforated flex pipe is an alternative to solid PVC pipe. It’s a bit lighter and comes in 100-foot rolls, but it’s more challenging to shape well against walls. A reliable flex pipe option is also available for the tail ditch. Remember that the footing drains can become useless if heavy rocks are placed on top of them during the backfilling process of the foundation.
Adding new drains to an existing water problem foundation is a labor-intensive project. It takes a skilled hoe operator to dig around an already-standing structure.
Over-excavation is often necessary to create stable earthen slopes where people can operate safely because the ground is typically unstable due to damp soils. If there is no waterproofing on the walls, the foundation must be scraped and power washed.
After the foundation is repaired and waterproofed, the drain pipe installation is the same as for a brand-new basement.
The Helpful Constructor
Software for Building Inspection and Code Enforcement (BICES)
Pete has been a building inspector for more than 30 years and has worked in both the public and private sectors. He has experience in both the office of building design and the field of construction in the Eastern United States, having worked on a wide range of projects from schools to treatment plants, individual residences, and condo projects to major residential landscaping projects. Wagsys LLC, which he co-founded in 2006 with two other building inspectors, developed software for city departments such as building inspection, planning, and zoning.