There are several ways a french drain system can be installed in a basement. Some systems rest on the footing, others below the floor, or even outside. These systems aren’t always interchangeable, and conditions specific to your basement should be the determining factor when choosing what type of system is best for you.
French drain systems have been around for centuries and have evolved over many decades. We will cover what a french drain is as it pertains to basement waterproofing.
The interior of the basement or crawlspace has a trench that goes around the perimeter of the foundation walls. In the trench should be a perforated pipe, and should be back filled with clean crushed stone. This will allow rising ground water to filter up through the stone and enter through the holes in the pipe.
On cinder block foundation walls, weep holes should be drilled into the bottom row of blocks. Plastic poly drain or a cove base drain is placed along the foundation wall, between the wall and the floor. This directs the water from the weep holes down into the system. Concrete is then poured over the stone and up against the poly drain to cap the system.
Any foundation wall cracks that develop and leak, water will also have the ability to pass down through the poly drain or cove base and into the drain system. The french drain system should be pitched slightly to a sump pit with an adequate sump pump to handle the maximum amount of water flow the system can experience.
This type of french drain system uses a patented rectangular pipe with cove base that rests on the footing, about 4″ to 6″ below the floor. Ideal for situations where hydro static pressure in the walls are a problem and you have little to no water table.
These systems are more economical then other systems and with little to no water table will perform just as well as systems that have deeper trenches. If you do have a water table against your foundation floor a standard system will perform better. Vapor transmission and hydro static pressure against your concrete floor can leave your basement feeling damp and giving off a musty odor.
This is the system we most commonly install. We use 3″ perforated PVC pipe set 7″ to 9″ deep and placed next to the footing. These are robust systems that handle hydro static pressure in the walls, and drop the water table below the concrete floor.
In some cases, it may be that a deep system is the best choice. These systems are at least 8″ to 12″ deep. We use 3″ or 4″ perforated PVC placed next to the footing. These systems perform identically to our standard system while lowering the water table that much more.