French drain depth: About 8 inches to 2 feet deep should be sufficient for many water-diverting projects, though related systems, such as those built around foundations and sub-ground living spaces, as well as the bases of retaining walls, may be deeper.
8-10” deep is good for a French drain. I suggest using a filter fabric to cover the pipe with holes. This will keep dirt from going into the pipe and clogging it up. As long as the the ditch and drainage pipe have fall (not under 1/8 inch per foot) then you should be good.
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.
A French drain needs to be surrounded by gravel in order to filter out silt and prevent clogging the drain pipe.
Tip #3: Place French drain below the frost line.
A properly installed French drain will begin at the depth of the base of the perimeter beam and is installed with a 1% minimum slope (1 inch in 8 feet). This is usually below the frost line.
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.
Line the Drain With Membrane to Minimise Blockage
Once your French drain is installed, maintenance is essential. Don't let it get blocked or you could end up with a moat around your building: great if you're looking to protect it from invaders – and not so great if you're trying to fight damp.
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.
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.
If you want to connect the French drainage system to the gutter downpipes from your home, consider using a 4-inch pipe rather than a 3-inch pipe. In heavy rain or bad weather, 3-inch pipes may not be able to cope with the amount of water that comes out of the downpipes flowing through them.
Contractors also prefer to work with a PVC French drain pipe. Despite its tough surface, it can easily be cut with a conventional handsaw. It's also easier to set the pipes at the proper slope and keep it in place.
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.
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.
Despite the design's best efforts, French drains get clogged by dirt, debris and silt. They do need to be cleaned out regularly – about once per year – to ensure that they continue to direct water away from the building's foundation. The best way to clean a French drain is mechanically, using an electric snake.
Connect with local French drain experts to help with your project. Installing a French drain yourself is possible but labor-intensive and time-consuming. Call 811 a week or two before you start your project to get your buried utility lines marked.
You'll likely need a permit since this project may require soil grading to avoid drainage issues. Repairing your floor may be more cost-efficient than replacing it if grading is necessary. No permit may be required to hang drywall on exposed wooden wall studs in your garage.
Yes, you should wrap the French drain's gravel-filled trench with a permeable filter fabric. This fabric helps to prevent soil and debris from clogging the drain while still allowing water to enter the system.
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.
Interior French drains are meant for waterproofing the basement or draining your crawl space. They cost more because contractors must tear out the basement floor (most often made of concrete), install the drain, and then repair it.
French drains are best suited for properties with moderate to severe water drainage issues, particularly in areas with heavy rain or poor soil drainage.
Use Natural 1-1/2" round rock for best drainage. Washed rock is ideal. Avoid small pea gravel as the spaces in between stone is smaller minimizing flow rates. Avoid Crushed Rock (minus) that compacts and has "fines" that will clog pipe inlets.