Foundation, Concrete and Earthquake Engineering

Foundation Drain System

Most homes built today have foundation drains to drain the water gathered around the bottom of the foundation away from the foundation to prevent it from leaking into the basement. The term foundation drain is frequently referred to as a French drain as they operate on the same principle, a ditch filled with gravel or stones that will provide a path for water to be diverted. Most basements that have water leakage problems are associated with the drainage system. The typical problems associated with drainage systems are that they are inadequate or the drainage system becomes clogged at the outlet.

The foundation drainage systems in modern construction consists of four inch perforated PVC pipe that is placed at the bottom of the foundation and covered with stone and fabric to catch the water and divert it around the house to a storm sewer or disposal area. 

Perforated PVC pipe in coarse filter mediaThe slope of the drainage pipe and outlet must be sloped downward to insure that the water runs away from the foundation. Although there are several techniques to installing foundation drains they all are designed to divert the water away from the foundation to keep the inside of the basement dry.

Appropriate backfilling and grading around the foundation is critical to for the system to work properly. The foundation backfill material should be either sand or gravel to allow the water coming of the house to drain down the foundation wall to the drainage system. In addition, the ground surface must be sloped away from the house so as much water as possible will run away from the house. The recommend slope of the finished grade is a 10 degree slope away from the house for approximately twenty feet from the foundation.
A typical solution for foundation drainage
French drain
 If the water is not drained away it will build up until there is sufficient hydrostatic pressure (water pressure) to force the water under the footing and up into the basement along the floor outer seems.
It is absolutely critical to check the drainage system outlet periodically to insure that it is not clogged. If the system becomes clogged the water will backup in the drainage system and around the foundation and eventually leak into the basement. If you have a foundation drainage system installed and water appears in your basement it is most probably caused by the drain system outlet being clogged. Removing the clog will immediately remedy the problem.


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