Dig a trench from the place in your yard that needs drainage to your chosen outlet. Check for underground utility lines and pipes before digging. The trench should be about 18 inches deep and 9 to 12 inches wide. least 1 percent, so the force of gravity will work for you.
Add and compact 3 inches of coarse drainage gravel in the trench. Place the perforated pipe on top of the gravel in the trench.
The minimum cover required when the drainage system is in a traffic area with drainage pipe diameters from 100 mm through 1200 mm (4”-48”) must have at least 0.3 m (12”) of cover over the pipe crown, while 1500 mm (60”) pipes must have at least 0.6 m (24”) of cover.
All drainage pipes should be placed on the gravel bed in the trench. PVC drainpipe, if used, should be placed in the trench with the holes facing down.
Typically, French drains are 18 to 24 inches deep, but they can be as shallow as 8 inches deep. However, they can be deeper if you live in an area with heavy rainfall and high water tables.
Without the gravel and the fabric, however, the drain can clog up with sand and soil over time. We're sorry, there seems to be an issue playing this video.
A professional can install an exterior French drain around two to three feet underground so it can move surface water away from your home and property.
A French drain installation is widely recommended to utilize a 4-inch perforated pipe according to industry standards, the velocity requirements of the water flow, and the potential connections for downspouts.
Clay soil has poor permeability, meaning it doesn't allow water to pass through easily. In such cases, the effectiveness of a French drain may be limited as the water may struggle to drain away from the area efficiently. French drains may not be suitable for areas with high water tables.
If installing the drain involves diverting a stream or affecting a wetland, you likely need a permit to move forward. Generally, a small French drain on your property that doesn't change the flow of runoff entering and exiting your yard won't need a permit.
Swales: A Natural Solution
They're a great option if you're looking for a more natural, eco-friendly alternative to French drains. A swale is typically lined with grass or vegetation that helps slow down and absorb water.
Installing a French drain costs $500 to $18,000, with a national average of $9,250. On average, you can expect to pay $10 to $100 per linear foot, or between $500 and $5,000 to have a 50-foot French drain installed.
8 cons of French drains
May require regular maintenance. Care must be taken not to hit utility lines when digging for installation. Installing them may involve digging up your yard or even pavement. If the pipe gets clogged, it can be difficult to find and fix the problem area on your own.
Distance from Foundation
A general rule of thumb is that a french drain should be installed around three feet away from the foundation of a home, but this can vary depending on individual landscaping factors such as where the water is pooling and where gutters are already aligned.
One of the most common pipe materials used to create a French drain is plastic because of its durability. There are two frequently chosen pipe variations: corrugated and PVC. Both are lightweight, but corrugated pipe can be flexible, while PVC is stronger and more rigid.
Aside from what we've listed here, the difference between a French drain and a trench drain is that a French drain is used for water that is underground while a trench drain diverts excess water from a surface.
Make sure you excavate the correct pitch (or slope) of your French Drain installation so that water drains into a sump, catch basin, or other drainage feature. There should be a 1-foot drop (sloping downward) for every 100 feet of pipe.
A French drain is a great solution for a wet basement or below-grade space, but, just like any other type of drain, French drains are susceptible to clogging. Soil and debris tend to build up inside the pipes, eventually stopping water from flowing.
Traditionally, you would fill it with gravel, but you may wonder if you have any alternatives. Could you instead fill it with sand? Yes, you can use sand instead of gravel for your French drain when your project calls for it. It is less effective than gravel, but it can get the job done.
A properly designed French drain system does not require an outlet. The water will simply soak into the soil as it flows along the perforated pipe. In fact, a French drain doesn't require an inlet on just one end either. You can construct the drain to accept water along its length, and disperse it underground.
The depth of the trench should be at least 18 inches to allow room for: A gravel base, Drain pipe, Rock gravel, Topsoil.
Know Your Digging Dimensions
A French drain needs to be surrounded by gravel in order to filter out silt and prevent clogging the drain pipe. Pre-drilled PVC pipe and flexible drainage pipes are commonly found in a 4” diameter. You will want at a minimum a 6” wide trench for a 4” pipe.