Learn everything you need to know about French drains. Bisson Expert explains the purpose of French drains, the different types of drains, and the signs to watch for to effectively protect your house’s foundation.
As a homeowner, understanding the different components is essential not only for proper maintenance but also for protecting your investment and ensuring your peace of mind.
In fact, when you understand the purpose of the various components of your property’s structure and are able to recognize the warning signs of a potentially dangerous situation, you can act quickly and thus prevent the worst from happening.
French drains are not widely known among the general public. However, 60% of basement humidity problems are linked to poor drainage (source: SCHL). that’s why French drains are so important!
What is a French drain?
A French drain is a drainage system designed to protect your foundation from humidity and water infiltration, especially when water tends to accumulate on the ground surrounding your house. The French drain can be connected to a catch basin in the basement, where a sump pump is installed to remove excess water, or it can be directed directly to the sewer system.
Depending on the layout of your building, one or the other of these configurations will be chosen:
- Exterior drainage, installed around the foundation by excavation.
- Interior drainage, installed beneath the basement slab at the perimeter of the foundation walls.
External drainage
Internal drainage
How does a French drain work?
A French drain uses gravity to draw water away from the house. It consists of a rigid, perforated pipe made of polychlorinated vinyl (PVC). These perforations allow water to enter the pipe, which is installed underground around the perimeter of the house. At least 12 in (about 30 cm) of crushed stone is added on top, covered with a geotextile membrane to prevent soil and sediments from seeping in.
What is the purpose of a French drain in a house?
A French drain is designed to protect a house’s foundation from water infiltration and flooding by collecting and diverting water that accumulates around the foundation footings.
If you’d like to learn more about the many tips available to help keep your foundation dry, feel free to check out our article on the subject.
video of the entire process
French Drain: Quebec Regulations and Requirements
In the province of Quebec, all houses built since 1955 must be equipped with a French drain. If you live in an older house, it’s quite possible that a French drain was never installed. You can consult a foundation specialist to find out for sure.
Things to know about older houses
Sometimes a house may not have a drain, may have a broken terraccotta French drain, or a clogged or outdated French drain. Check with your local municipality to learn more about regulations and local requirements. This will help you ensure that your property complies with all regulations.
Types of French drains
There are several types of French drains in Quebec. These include rigid PVC drains (BNQ), flexible PVC drains (agricultural drains), and terraccota clay drains. Here is a detailed description of the advantages and disadvantages of each of these options.
[ 1 ] Rigid PVC Drain (BNQ)
The rigid PVC drain (BNQ) is made entirely of plastic, both inside and out, which gives it excellent strength and the longest service life of any available option.
In addition to its exemplary strength and performance, this pipe is equipped with cleaning ports, which greatly facilitate its inspection and maintenance.
| Pros of Rigid PVC Drain | |
|---|---|
| Strength and durability | 
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| Optimal water flow |
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| Easy to clean and maintain |
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| Resistance to iron-rich soil |
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| Suitable for Quebec’s climate |
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| BNQ certification |
|
[ 2 ] Corrugated Plastic Drain (Agricultural)
Before the advent of PVC pipe, the corrugated plastic drain—also known as an agricultural drain or “Big ‘O’”—was contractors’ top choice due to its ease and speed of installation. Thanks to its flexibility, it allows for seamless connections to the corners of the house.
It is still permitted under the building code, but iron orchre is impossible to remove, and its fragility makes it impossible to extract roots without breaking it.
[ 3 ] Terracotta Drain
Terracotta drains have not been used in Quebec since the 1970s.
Since they lack any mechanism to prevent roots and soil from infiltrating, these French drains are now rather outdated and usually need to be replaced with a newer type of drain.
Lifespan of a French drain and signs to watch for
In general, and based on our fieldwork, a French drain lasts between 30 and 40 years. However, certain situations can shorten its lifespan. Even in a new construction, many factors can cause the French drain to deteriorate or reduce its effectiveness.
A clogged French drain
It’s very common for particles to accumulate in a French drain. These minerals, grains, and dust come from the soil and the water flowing around it. If the amounts are significant, they can even clog the drainage system after just a few years.
Fortunately, drain installation has improved with advancements in modern construction, and several steps are now taken to protect new drains.
An improperly installed French drain
Unfortunately, some builders haven’t quite mastered the art of installing French drains. It’s common for new drainage systems to be installed incorrectly or to lack sufficient crushed stone.
If you have any doubts, a camera inspection of the drain can reveal whether the levels are correct or if certain sections may have been crushed or bent. Sometimes the drain is simply not installed at the correct depth. The junction between the footing and the foundation wall is more likely to allow water to seep through, which will accumulate in the drain. You will then notice the junction between your interior concrete walls and floors becoming damp or even soaked during heavy rains.
A French drain at the end of its lifespan
Finally, it’s important to note that French drains have a limited lifespan depending on their components and the surrounding conditions, just like any other building material. Replacing a French drain is part of the routine maintenance required for a property.
On the other hand, if your soil is sandy or there is significant vegetation, the lifespan of the French drain may be reduced. In areas prone to iron-rich soil, iron particles in the soil quickly clog drainage systems. These systems must then be replaced with chimneys that allow for regular cleaning.
Frequently Asked Questions (FAQ)
Q : How can you tell if a French drain is defective?
R : Signs that a French drain may be defective include constant dampness in the basement, water seepage after rain, mold, efflorescence, or a sump pump that is not functioning properly.
Q : What is the lifespan of a French drain?
R : A French drain lasts between 30 and 40 years on average, depending on the material used and the quality of the installation. PVC pipe is the most durable material among the three types of French drains available.
Q : How do I know if my drain needs to be cleaned?
R : You can perform a camera inspection through the access ports of your French drain to determine whether cleaning is needed.
Need a French drain? Trust Bisson Expert
A new French drain is a sound investment for your property, as it will help keep it in good condition and prevent serious problems. If you think your home’s French drain needs to be replaced and would like to get a quote, we’re here to help.
At Bisson Expert, we’ve been working on foundations for over 70 years. We use the best methods for installing French drains and can advise you based on your specific needs. Our experienced team is here to listen to you and help you regain your peace of mind.
An effective drainage system, combined with foundation waterproofing, is the best combination for protecting your property and your belongings.