How much does a French drain cost? How much gravel should I put down? What size pipe do I need? These questions are common for homeowners who want to install a french drain system.
A French drain is installed around foundations or other areas where water collects. The purpose of a french drain is to prevent moisture from entering walls or other structures.
A French drain costs between $10-$100 per linear foot, depending on the soil type and surrounding conditions. If you live in a flood-prone area, you’ll likely need to add additional materials such as sand and stone.
The amount of gravel needed depends on how deep your french drain needs. Typically, 1″ – 1/2″ of round rock gravel will suffice. Avoid the pea-sized gravel as it creates a small space between the small stones obstructing the flow rate.
To calculate the cost of installing a french drain, multiply the length by the width. For example, if you’re planning on installing a french drain along a driveway, you’d multiply the length (in feet) by the width (in feet).
It would help if you covered the pipe with 3″ of gravel to cover the pipe completely.
What is French Drain? How Much Does it Cost?
A French drain is an underground system consisting of a trench filled with gravel or rocks and a perforated pipe placed at the bottom of the ditch. This type of drain is used to collect surface water runoff and prevent flooding.
We usually install French drains at lower elevation areas where there is excessive rainwater or groundwater collected. Rainwater flows down the grassy area and collects at the edge of the property. If no control measures are taken, this water will eventually overflow onto the road.
When the water overflows, the water starts seeping through the gravel and enters the pipes through its holes. The water enters the French drain and moves further down to the sewer line. The water then travels to the sewer line and empties the city sewers.
The water that seeps into the soil starts settling in the groundwater once the groundwater gets high enough to reach the bottom of the french drain, it again into the french drain to move out from the same outlet.
French drains can help reduce the risk of damage caused by flood waters. They are also used to protect against erosion.
The size of the pipe depends on how much volume of water needs to be drained. Generally, the larger the pipe, the more effective it is. Pipes can range from 4 inches to 12 feet deep.
How Should I Build a French Drain?
To install a French drain, dig a trench around the perimeter of the area requiring drainage. Next, lay down a layer of landscape fabric or geotextile over the entire length of the trench. Then, place a perforated pipe along the center line of the trench. Finally, fill the trench with gravel.
Install the french pipe at the lowest elevation grade, so the water does not sit inside the pipe.
Factors to take into account for calculating the French Drain Cost
The National Association of Home Builders says that many factors are involved in calculating the cost of a French drain installation. These are the property size, soil type, drainage area, and whether it is being done for the new home construction or retrofit work. According to Forbes, the national average cost of a French drain is approximately $5000.
Here are the factors that influence the cost of the French Drain:
Cost of Labour
The average labor cost for installing a french drain ranges from $50 to $100 an hour, depending on how much excavation needs to be done. If there are complications, such as breaking up concrete with a jackhammer, excavation can take longer, increasing the overall project duration. Labor costs increase because of the difficulty accessing the site and the amount of material needed to dig the trench.
Material and Type
In terms of materials, there are several options to consider. You could go with a PVC pipe, which is inexpensive but requires some skill to lay correctly. You could opt for concrete pipes, which are expensive and require professional help. Or you could try one of the many precast systems out there. These come in various shapes and sizes and are generally easy to install. They often include a sleeve that prevents soil from getting into the drainage system.
While perforated pipe costs around $100 to $200, adding a sump pump to your french drain installation can add up to $2000.
Length, Size, and Depth
A French drain’s size, length, and depth are important factors to consider when choosing one. A small, inexpensive drain might work fine for you, but it will only do a little good if it reaches far enough into the ground. You’ll end up wasting money digging holes every few feet along the perimeter of your house.
On the other hand, a significant, expensive drain that reaches deep into the soil could cause problems. The drain could clog and overflow if it needs to be longer to reach the septic tank. And if it extends too deeply into the ground, it could interfere with groundwater flow beneath the foundation.
For an exterior french drain, you may need to pay $10 to $35.
You’ll likely need a grading permit if you plan to dig a hole in your yard. It allows you to excavate soil without applying for a separate construction permit. Sometimes, you may need a storm-water management permit, which helps prevent runoff into waterways during heavy rains.
The average cost of a permit ranges from $50 to $100. It also serves as an official notification about the type of work you will excavate. A local inspector may come over to check if the drain pipe and gravel meet the local codes and if the trench is secure.
Location of the French Drain
As we know, interior drains are labor intensive and thus require more labor work than exterior drains. Along with the required drain size, the location also plays a pivotal role in deciding its cost. Most of the basements require around 100 feet to 150 feet of french drain resulting in an expense of $5000 to $13,500.
- Cost of Interior French Drain
The price range for an Interior french drain is around $60 to $90 linear per sq. foot. 80% of the cost accounts for labor. Adding a sump pump can cost you up to $2500 additionally.
2. Cost of Exterior French Drain
As Exterior french drains are easier to install, you must pay $30 to $50 per linear foot. But if you are located around the wet areas where the soil remains wet, you need to install them closer to the foundation base, resulting in higher costs.
3. Cost of Gravel
To calculate the gravel needed for a French Drain, multiply the length of the trench times the width and depth of the trench. For example, if the trench is 10 feet wide and 8 feet deep, the total area would be 80 square feet. Multiply 10 x 8 80. Divide 80 by 2.2 to determine how many cubic yards of stone are required. In this case, it would be 40 cubic yards.
If you want to know how many bags of rock fill you need, divide the amount of gravel needed by 1.5. So, if you need 40 cubic yards of gravel, you will need 25 bags of rock fill.
Frequently Asked Questions
How should I calculate the French Drain Size?
To calculate the size of a drainage system, multiply all surface area (the total square footage), slope, and average rainfall. It is how we calculated the size of our French drains.
What is the difference between a French Drain and a Sump Pump?
A French Drain is used to collect water that flows through the soil. The water then goes to the lowest point in the house or basement. A sump pump collects the water and pumps it outside.
Where do I put my French Drain?
You can place your French Drain anywhere on the property. However, it’s best placed near the foundation of the home.
Can I save money when installing a French Drain?
Yes, there are ways to reduce the cost of installation.
- You can choose a smaller-sized French Drain instead of a larger one.
- You can use concrete instead of clay.
- You can use a precast drainpipe instead of digging trenches.
- You can use a prefabricated French Drain instead of building one yourself.
- You can use a low-cost material such as plastic pipes instead of metal pipes.
A French drain may appear to be an investment-intensive affair at the installation time. But it prevents water from entering the basement and saves you from costly repairs. It is even recommended to install a French Drain before starting construction of a new home.