Keeping Basements Dry by Larry Diamond

Author:Larry Diamond
Language: eng
Format: epub
Publisher: Storey Publishing, LLC
Published: 1978-03-25T16:00:00+00:00

Foundation Drains

Materials needed: drain pipe (PVC, flexible, or ceramic), felt paper (for ceramic pipe), pea gravel or crushed stone

Perimeter foundation drains should be installed after the walls have been treated. Drain pipe or drain tile comes in three types: PVC (polyvinyl chloride), flexible molded, and ceramic. The type you choose will depend on the price and on how much you wish to support the petrochemical industry. In any case, the pipe comes in standard 4-inch diameter size. PVC is perforated and comes in 10-foot lengths, the molded flexible pipe comes in rolls of up to 250 feet, and ceramic pipe comes in 4-foot lengths.

Lay the pipe on a 3-inch bed of pea gravel or crushed stone. If ceramic pipe is used, place the sections ¼ inch apart and wrap the joint with an 8-inch strip of felt paper. This keeps soil and silt from clogging the joint while allowing the water to get under the paper and into the drain.

Install PVC pipe with the perforations facing down, to minimize silting. Flexible pipe needs no special treatment.

Because the purpose of installing perimeter drains is to carry the excess ground water away from the building site, you need to be concerned with where the runoff will go. If permissible in your locality, you can run the water off into a storm sewer. If you live in the country and the house is on a slope, you can simply run the pipe from the low end of the foundation to the surface some point below the house. If your lot is level and local building codes prohibit connections to storm sewers or if no sewer is nearby, then there are at least two alternatives to consider.

One is the construction of a dry well or modified leach field. These are subsurface water-collection points that allow for normal absorption into the soil at a distance from the house. The second alternative is to connect the perimeter drain to a sump and then pump the water to the surface (see the section on interior drainage and installation of sump pumps).

For dry wells there is no rule of thumb concerning the proper size. A “dry” well simply holds the water until the soil can absorb it naturally. If your soil is heavy, the well will drain more slowly and you will need a larger well. The opposite is true for sandy soils; the same size house will need a smaller well. Before installing a dry well, it is recommended that a soil engineer or representative from the SCS be consulted. A percolation test should be performed to determine the rate of absorption, and you will need an estimate of the maximum expected water flow from your drainage system. The dry well can then be constructed based on the maximum rate of flow and the soil absorption rate. A well that is too small could back up your system resulting in a flooded basement — which is what you are trying to prevent!

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