How deep should you dig a French drain

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.

How wide and deep does a French drain need to be?

The trench should be about 18 inches deep and 9 to 12 inches wide. French drains need to have a slope of at least 1 percent, so the force of gravity will work for you. This means that the drain should slope down a total of at least one inch for every 10 feet of pipe.

Why do French drains fail?

Over time, a French drain may become clogged. Tiny soil and clay granules slip through the pores of the landscape fabric and gradually build up inside the pipe. Another common cause of French drain clogs is root intrusion from grass, shrubs, and trees.

How shallow can a French drain be?

Add a Layer of Topsoil to Drainage Ditch Dig a trench along the outside of your footing. The trench should be at least 2 feet wide, and can be as deep as 6 feet for a basement or as shallow as two feet for a slab-on-grade home.

What size gravel is best for French drain?

Gravel used for this layer is typically 1/2 inch to 1 inch across — the larger it is, the better the water flow and less chance of clogs and blockages. For a French drain without a perforated pipe, opt for even larger gravel, such as 1 1/2 inches across.

Can a French drain catch surface water?

A French drain is a long trench with a perforated pipe surrounded by gravel. French drains control groundwater and a moderate amount of runoff or surface water. A catch basin is a box set into the ground with a grate on top. Catch basins control large amounts of runoff and surface water but do not control groundwater.

How deep should drain pipes be buried?

Maintaining a depth of 12 to 18 inches is best for drain pipes, but the depth of the pipe may vary in order to maintain a downward slope, which is critical for proper drain functioning.

Are French drains worth it?

French drain systems are incredibly effective because, unlike typical surface drains, they collect water over the entire length of the drain as opposed to one dedicated area. The force of gravity helps to guide water along a reliably smooth path to a desired discharge point.

What is better than a French drain?

If you have a negative sloped yard (which slopes toward your foundation), a surface drainage system is a better choice than a French drain. Sloping of more than 1”-1-1/2” on a 10′ run can result in excessive amounts of water seeping beneath your house.

Can a French drain go uphill?

In a French drain, accumulated water flows naturally down an ever-so-slightly-sloped pipe. As long as you have gravity, you’re good to go. … If, however, your property is completely flat or a portion of your drain runs uphill, you’ll need to pump the water or run your pipe across an adjacent sloping property.

Article first time published on

How much gravel do I need for a 100 foot French drain?

How much gravel do I need per foot of French drain? You would need around 0.72 cubic feet of gravel per foot length of French drain for a typical French drain width of 10 inches and a depth of 12 inches if you’re using a 4″ drain pipe.

How many years does a French drain last?

Properly installed drains use advanced plastic sheeting called geotextile to protect the drainpipe from a blockage. French drains can last decades before needing maintenance. If your home requires a sump pump, a high-quality model will last around ten years before needing replacement.

Can I use river rock for French drain?

Hard rocks such as granite or river gravel prove viable options for a French drain because they won’t break down over time as much as other rock varieties, such as sandstone and limestone.

How deep underground is a sewer line?

Sewer lines on private property can be as shallow as 18–30 inches deep or as much as 5–6 feet deep. In areas with cold climates, the pipe will be buried deeper to prevent freezing in the winter.

How deep should rainwater pipes be?

According to ‘The Department of the Environment’, they recommend that pipes should be buried at least 600mm (two feet) underground. At this depth, the soil acts as a natural insulator and prevents them freezing.

How much water can a French drain handle?

Generally, a French drain should drop at least one percent in depth for every 100 feet of length.

Can you put topsoil over French drain?

The simplest drain is a classic French drain, which is nothing more than a trench filled with coarse stone or gravel. … The drain can be left open or, if aesthetics are a concern, can be covered with a couple of inches of topsoil and sod.

Does French drain Need outlet?

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.

How do you grade a French drain?

A French drain needs a slope of no less than 1%. That means from the highest point of the drain field all the way to the drain exit, the system should slope at least 1 inch for every 8 feet of length.

What's better French drain or trench drain?

While French drains deal with water that’s underground, trench drains divert excess water away from the surface. … These drains are great for managing excess rainwater and stormwater in concrete areas such as parking lots, sidewalks, and driveways.

When should a French drain be installed?

When you have a problem with surface water, such as a soggy lawn or a driveway that washes out.
If water is getting into your basement.
If you’re building a retaining wall on a hillside.

How much does a French drain usually cost?

According to Fixr, the average French drain costs $4,500. An exterior drain located fairly close to the surface could cost as little as $1,000, or $25 per linear foot on average. Drains installed under your basement floor could cost $2,000 or more. Expect to pay $60 to $70 per linear foot for installation.

How do you Trench a drain for a yard?

Dig a trench that is 18 inches deep and 9–12 inches wide. Lay water-permeable landscaping fabric in the trench, followed by 3 inches of gravel. Lay your perforated drain pipe in the trench, cover with an additional 3 inches of gravel, and cover the drainage ditch with rocks, soil, or stones.

Should a French drain have standing water?

French drains are designed to collect rainwater and channel it downhill. If surface water is standing in low areas of the yard that are supposed to flow into your French drain, you have a drainage problem. If the low areas of your yard are as firm and dry as higher spots, then your French drain is working as expected.

Does every house need a French drain?

If you are a homeowner with a wet basement or a moisture-laden yard, you can likely benefit from a French drain. … Any issues with surface water along your property should also spur the installation of a French drain. If your driveway washes out, it is a clear sign you need a French drain.

How do you divert water on a slope?

Construct a French drain.
Build a rock drainage ditch or swale.
Terrace the hillside to stop soil erosion.
Build a berm or mound that redirects water.
Plant the slope with trees or grass to soak up floodwater and hold soil in place.

How do I get rid of standing water in my garden?

Landscaping. One of the best ways to deal with standing water is to change the topography of the garden. Water will naturally flow downhill, so if you can create a lower point in the garden next to the external drainage system, you can channel the water away. A berm is another great way to prevent standing water.

Can I use pea gravel for French drain?

Do NOT Use Pea Gravel, Pea Pebble, Pea Stone When Building a French Drain. When building a French drain, you want to use a coarse rock that has been screened and washed. The rock that you see in this French Drain is 3/4″ and larger. You end up with large voids that’ll move far more water.

Can you use landscape fabric for French drain?

The best type of fabric for a drainage project such as a drain field or french drain is non-woven geotextile landscape fabric. If you’re project requires high strength and also good drainage then a high end combination woven fabric could be suitable for your application.

How far from the house should a French drain be?

How Close Should a French Drain be to the House? A good rule of thumb is to install french drains 3 feet from the house. Make sure to measure around the porch, patio and deck.