French Drain Dimensions: Everything You Need to Know
Make sure your French drain measures up to the task
Highlights
A four-inch diameter perforated French drain pipe running five to ten feet is the standard size.
A large French drain is necessary for areas that experience heavy rainfall and extreme storms.
Low soil permeability can cause waterlogged soil and slow drainage issues.
Small French drain pipes are more susceptible to clogging and are more difficult to maintain.
When building an effective French drain system, size is the key to success. You’ll want to choose French drain dimensions that are the adequate size for draining away excess water around your home. Otherwise, your water issues might continue and cause further damage to your house and yard.
To choose the right size drainage pipe, you’ll have to consider many different factors, such as how much water needs to drain and the type of French drain. Let’s review French drain dimensions and when to hire a French drain specialist to help with your installation.
What Is the Standard French Drain Size?
A four-inch diameter perforated French drain pipe running five to ten feet is considered standard sizing for most applications around your home. If your home experiences heavy amounts of water accumulation or has very saturated soil, you might need to install a larger diameter pipe. Consult your local French drain installer to determine the right size drain pipes for your needs.
Since French drain pipes are installed almost entirely underground, you’ll only see the opening of the pipe, also known as an exit point. This makes them ideal for anyone who worries about the eye-sore factor that comes with most drains.
French Drain Types
French drains come in many shapes and sizes, but each has the same job—to divert water away from your basement and foundation. Here are the different types of French drains and their common dimensions.
| Type of French Drains | Dimensions |
|---|---|
| Surface French Drain | The trench should be about 18 inches deep and 9 to 12 inches wide |
| Blind French Drain | Grates vary in size |
| Interior French Drain | 4 inches to 8 inches diameter |
Surface French Drain Dimensions
Surface French drains redirect water collecting above the ground in your yard. Homeowners with sloped driveways often use these drains to help with runoff that collects during heavy rain or snow melting.
A small trench needs to be about 18 inches deep and up to 12 inches wide. The exact depth of a French train trench should be determined with the help of your drain installer. A PVC pipe sits in this trench with metal grating above it. Water is collected and directed out to the street or through city water systems.
Blind French Drain Dimensions
Blind French drains are typically called blind inlets. They consist of a pipe that drains water away from the lowest points of your yard. Crushed stone and a drain cover is placed over the pipe to conceal and protect it.
Pipe and drain sizes vary depending on how much water it needs to drain. Drains in low-lying areas prone to flooding need large systems to collect and redirect water. Small household systems for slanted yards don’t necessarily need to be as wide.
Interior French Drain Dimensions
As the name implies, interior French drains are installed inside your homes in low areas like the basement. These drains are pipes installed along the bottom of your basement walls. The pipes are often four to eight inches wide and the length of the basement walls they’re installed into.
Some of these pipes lead to a drainage outlet while others are connected to a sump pump for added efficiency.
Choosing the Right French Drain Size
Picking the right size French drain is important so you have optimal drainage where you need it. Several factors impact the size of your French drain, including the following:
Water Volume
The amount of water to drain away from your home is the most important thing to consider when choosing a French drain size. Make sure that the drain can keep up with the largest amount of water you’re likely to need drained. To figure out how much water it needs to hold, refer to local rainfall totals and other sources of water, such as nearby streams and ponds.
Permeability of Your Soil
Soil permeability (how quickly the ground soaks up water on its surface) is another crucial factor in choosing a French drain size. If your soil is not very permeable, which is common in soils with a lot of clay, a larger French drain is best suited to avoid waterlogging. Consider testing your soil before choosing a French drain size to ensure it aligns with your pipe depth and size.
Site-Specific Factors
You must consider site-specific factors when deciding where to place your French drain. These yard factors include the slope of your property, its layout, and existing natural drainage patterns. Ideally, you want to accommodate the yard’s features and drainage to ensure the installation doesn’t disrupt the natural flow.
Maintenance
You’ll want to build your French drain system with maintenance requirements in mind. Smaller French drains can be more difficult to inspect for damage, clean, and unclog. Debris can easily become lodged inside small drain pipes and may require more frequent professional cleanings.
What to Do if You Have the Wrong Size French Drain
If you have the wrong size French drain, you might still be experiencing issues with waterlogging or other water damage to your home. If that’s the case, you have a few options. You can replace your French drain with a larger-sized one or you can support water drainage by installing a supplemental drainage system.
The best way to know what option suits you best when trying to correct a small French drain is to contact an expert, such as a drainage specialist near you. These French drain pros can help you decide which solution is best, and they can also give you a quote for how much the work would cost.