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Interior of a foundation drain sump pit and pump as viewed from the top

Foundation Drains


Purpose of a Foundation Drain

Diagram showing outside forces on a foundation

Wet soil affects the foundation with more lateral pressure than dry soil.  To mitigate the forces from water buildup in soil, geotechnical engineers design the foundation with a way to collect water that seeps in around the foundation, which is the foundation drain. 

 

The foundation drain consists of a perforated pipe around the foundation (below the basement floor elevation), which collects water that has seeped into the soil.  As water seeps into the soil around a foundation, the water is collected in the pipe and discharged into a sump pit, where it is pumped to the outside by a pump.

 

If you have them, the small drainage inlets at the bottom of your window well are typically connected to the foundation drain pipe.

 

For additional basic information on foundation drains, refer to the Foundation Drain Components.  

Foundation Drain Design

If you have a foundation drain and a sump pump in your home, it was specified in the soil report by the geotechnical engineer.  You should be able to find a cross-section drawing of your foundation in your home's soil report.  If the detail does not show a pipe, you may not have a foundation drain around your foundation.


Foundations are addressed in Chapter 18 of the International Building Code (IBC) and Chapter 4 of the International Residential Code (IRC).

Sump Pump Components

Pipe Trench

The crushed gravel and geofabric filter the water entering the pipe.  In a properly functioning foundation drain system, the water flowing through should be minimally cloudy.

Cross-section diagram of a perforated foundation drain pipe with gravel wrapped in geo-fabric like a

Common Foundation Drain Conditions

The design of a foundation drain system is generally standard in the engineering industry.  It consists of a perforated pipe wrapped in gravel and filter fabric (geo-fabric), somewhat similar to a burrito. 

 

The foundation drain collects water that seeps in from the soil through the geo-fabric and gravel, which act as a filter and convey the water to the sump pit through the pipe.  A foundation drain system can have more than one sump pump.

 

If installed correctly with gravel and geo-fabric, foundation drain pipes should be relatively clean and the flowing water relatively clear.  In addition, if sloped correctly and constructed with the proper type of pipe, there should be no compressed sections or low points with standing water.

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BLOCKED PIPE

Soil and debris in the foundation drain pipe impede the proper flow of water.  Soil and debris can be deposited into the pipe during construction by improper construction methods.  Also, soil can enter the pipe after the backfilling of the foundation if the gravel and geo-fabric are not correctly installed.   This is typically due to the actions of the contractor and can be a construction defect.

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PIPE SLOPE

Pipes with insufficient slopes can be problematic.  However, just because there may be low or flat spots in the foundation pipe system does not always mean the system is not functioning properly.

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PIPE DEFORMATION/DAMAGE

A compressed, crushed, or broken pipe can be caused by one or more of the following:


  • Improper type of pipe used.

  • Damage to the pipe after installation. 

  • Damage to the pipe during soil backfill operations.


These types of conditions are often the result of the contractor's means and methods and are common in construction defect claims.


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