The present article explains foundation drainage, its’ importance, advantages, and the types of foundation drainages. Further, foundation drainage is often a DIY work that you can install with some tools.
However, you may also take professional help. The foundation drainage installation steps enlisted in this article shall take you through the detailed installation procedure.
What Is Foundation Drainage?
Foundation drainage is an underground drainage system. It collects the subsurface water into a perforated pipe and drains it into a soak pit or sewer system.
The motive of providing foundation drainage is to protect the foundation from water-caused ill effects. Foundation drainage is a must-have for buildings having a basement built on low-pervious soils. Why? We’ll explain it shortly.
Since a solid foundation is a must-have for a stable and strong house, once the foundation is damaged or exposed to the atmosphere, the house begins to develop cracks, tilt, or settle.
In extreme cases, the houses may collapse or overturn due to foundation instability. In many such cases, water is the main culprit. The soil behavior changes in the presence of water.
The soil loses its’ rigidity, exerts more pressure, tends to settle, and whatnot. Therefore, it is necessary to have foundation drainage that can safely discharge the free-flowing subsurface water.
Why Is Foundation Drainage Important?
International Residential Code (IRC) covers the foundation drainage topic in Chapter 4: Foundation, Section R405. The code states-
“Drains shall be provided around concrete or masonry foundations that retain earth and enclose habitable or usable spaces located below grade.”
The soil backfilled after the construction of the basement is loose. It has more voids, and thus the water easily seeps through it.
Therefore, the basement of a house is most susceptible to the problems arising from water ingress, such as water leakage, mold growth, electrical damage, bad smell, paint discoloration, and peeling-off paint.
Also, the saturated soil exerts excess pressure on the foundation. Hence, posing a threat to the structural integrity of the building.
However, the code emphasizes that a foundation built on well-drained soils doesn’t need foundation drainage. The reason is obvious that the soil is capable enough to allow the water to percolate to the deeper strata without a drainage aid.
Advantages Of Foundation Drainage
There are several advantages of having foundation drainage.
- The basement is dry and leak-free.
- The basement with foundation drainage has more utility than a wet basement.
- The maintenance cost of the basement is lesser.
- Well-installed foundation drainage is maintenance-free.
- It improves the house’s green building rating, e.g., LEED rating.
- Foundation drainage prevents the structure from damage due to water leakage.
- The water stagnation is nil hence no mosquito breeding.
- It increases the property value.
Disadvantages Of Foundation Drain
- The installation of foundation drains requires rework of landscaping.
- The chemicals injected into the soil for plant growth may seep into the water and pollute the stormwater.
- The buried drainage system needs excavation in case of pipe clogging.
Types Of Foundation Drainage
The foundation drainage is of two types based on functionality and positioning.
- French Drain
- Footing Drain
1. French Drain
Henry French of Massachusetts, USA, popularized the French drain in the 1800s. A French drain is installed along the perimeter of the house. Therefore, it is also known as perimeter drain.
The backfilled soil along the house perimeter is backfilled after construction is in a loose state. Therefore, a perimeter drain is necessary to drain off the water flowing through the loose soil.
A French drain contains a perforated pipe that collects water from the soil. A permeable mesh (sock) covers the drain pipe. It prevents the clogging of the drainpipe with soil.
A gravel blanket covers the drain pipe and the sock arrangement that acts as a filter. The biggest-sized gravels are closer to the drainpipe, and smaller-sized gravels are at the periphery. The complete system is buried underground.
Maintain a gradient of 1:50 to 1:100 to the drain.
2. Footing Drain
A footing drain is the drainage system at the footing level and contains a perforated pipe surrounded by porous material. It collects the water at the footing level.
Constructing the footing drain along with the foundation is beneficial. The footing drain has a gradient to drain off the water to the sump pit. Also, an electric motor is installed in the sump pit to discharge the sump water to the sewer system.
Technical Considerations For Foundation Drainage
The depth of foundation drainage depends upon the purpose of water drainage. For example, if the drainage is for surface water only, shallow depth drainage serves the purpose.
Otherwise, for stopping the seepage into the basement, the recommended depth of the drainage is at the foundation level. The minimum depth of the foundation drainage is 1 m. At this depth, the drain collects the maximum volume of the water.
However, in the case of mat or raft foundation, the drainage should be below the raft level. Also, for buildings with basements, the drainage depth should not be lesser than the basement depth.
The drain with slope discharges the water by gravity, and hence no need for a pump. The gradient is directed away from the house and towards the sewer system.
As explained earlier, the foundation drain slope depends upon the volume of water collected and the size of the pipe. For an increase in water volume, the gradient should be steeper, having the same pipe size.
Similarly, upon increasing the pipe size and keeping the volume of water the same, a lesser slope is required. The thumb rule for the slope of a French drain is 1 inch for every 8 feet of length, i.e., 1:96. Say 1:100.
The IRC R405.1 recommends the following points concerning the foundation drainage-
“Gravel of crushed stone drains shall extend not lesser than 1 foot beyond the outside edge of the footing and 6 inches above the top of the footing and be covered with an approved filter membrane material.”
Installation Method of Foundation Drainage
The installation method for a French drain is as follows-
- Mark the proposed layout of the water drain, existing sewer system, and all the levels.
- Verify the proposed layout and connection details with the slopes and levels at the site.
- Estimate the depth, width, and length of the trench and make the drawing.
- Excavate the trench as per the drawing.
- Lay the filter material at the bottom of the trench (thickness > 2″).
- Install the pipe with perforations downs.
- Fill the sides and top of the pipe with the filter material (top and side cover > 6″).
- Connect the pipe with the existing sewer system or sumps.
- Backfill the trench with the soil.
A foundation drain is an essential part of a building, especially in heavy rainfall and snowfall area. The French drain and footing drain are two types of foundation drainages.
Some contractors consider surface drainage as foundation drainage, but that is not true. However, surface drainage is also helpful in draining the water without seeping into the deeper ground.