Flooding French drain

Getting to know French drain systems

You have all kinds of drains in your home; all sinks and tubs have it, and there’s probably a drain near your washer. But did you know that there is a very large drain outside your home? This is called your peripheral drain system or French drain system. If this system does not work properly, the basement or crawl space will become wet or even flooded.

What is a perimeter drain?

A perimeter drain is a device that every home has and is designed to prevent water from seeping into your basement. It is intended to attract water into the soil that has accumulated as a result of heavy rains, melting snow or rising groundwater. It then carries the water away from your home, so it’s less likely to seep through your basement walls. Many years ago, clay tiles were used to divert water, and the name weeping tile remained thereafter. Nowadays, perforated pipes are used instead of tiles. It is also sometimes called a French drain, as this method of drainage was popularized by Henry French of Concord, Massachusetts, in the 1800s.

How does it work?

A perimeter drain, or weeping tile, is a perforated plastic or PVC pipe, which is installed underground, around the perimeter of your home. Perforations consist of thousands of tiny holes or slots that allow water to enter the pipe and be evacuated away from the foundation of the house. The pipe is normally covered with a permeable membrane that prevents earth from entering the pipe. It is then covered with layers of graduated gravel (the widest layers of gravel near the pipe, followed by smaller gravel) and is subsequently backfilled with earth. Gravel allows water to flow to the drainage pipe, without letting dirt and debris clog it. The drainage slab is installed in such a way that it moves away from the house and carries water to the main sewer system.

When a house is built, a certain amount of soil is excavated around the perimeter of the house. Once the construction is complete, this earth is put back in place, making it looser than the intact ground that adjoins the house. As a result, water flows more easily through this floor, which is right next to your basement or crawl space walls. This is one of the reasons why it is important to have a good perimeter drain to evacuate water from your home. Hopefully, when the contractors completed the installation of the perimeter drainage system, they took the time to properly pack the soil into place and make sure the soil tilted away from the house to improve drainage. A good inclination, in addition to a good functioning of the perimeter drains, is absolutely essential to prevent water infiltration. The majority of experts recommend a downward slope of 2.5 to 6 inches over a distance of 10 feet, away from the foundation.

It is then the responsibility of the owner to maintain the appropriate slope. If you’re planting trees, laying new grass, or installing a pool, you could change the way water flows out of the house. If you have unintentionally run water to your neighbour’s property, you could be sued and will be responsible for any costs incurred to correct the situation.

Be on the lookout for symptoms to avoid Flooding French drain

If your drain does not perform its function as it should, there will be signs, such as a much higher humidity level in the basement. It can even lead to mold or rot on the floor and lower parts of the walls. On bare concrete surfaces, you might notice a whitish crystalline powder, a phenomenon known as efflorescence. Eventually, water will seep into the basement between the footing and the base of the foundation walls or through cracks in the concrete slab of the floor.

In the latter case, before concluding that the drain is defective, you need to make sure that the water does not seep in for another reason. The problem can be, for example, a crack in the foundation wall or a defect in the outer sheath of the building (cladding, windows, doors, balcony, etc.). To make sure, it is usually enough to bare part of the basement wall. Another way is to wait for a period of drought and abundantly water the soil near the foundation.

The different problems and causes of French drains

Over time, French drains can become clogged with dirt, roots or other debris and will no longer be able to drain water from your home. If the drain is clogged, water can seep into the wall of your concrete basement because it has nowhere to go. Concrete is not waterproof, so it is very important to keep the water away.

Old houses sometimes feature clay or concrete tiles that degrade, collapse and become blocked with dirt and roots over time. You may need to replace the entire system with a modern plastic slab or, in some cases, you can simply replace the damaged sections.

If the tiles are blocked, but they have not collapsed, it is possible to clean the installation. A professional can dig access points around the basement walls to access and clean the drain. Some old drainage pipes have edges inside that make them impossible to clean. These should probably be replaced.

If you are replacing your system, consider installing a cleaning opening. It is accessed from the surface, so you don’t have to worry if the system needs to be cleaned at some point in the future.

In newer houses, the failure is usually caused by improper installation (counterslope, crushed pipe, insufficient fine gravel, etc.). In areas where the soil is rather sandy and ferrous, drains can also be blocked by reddish mud, iron ochre, if the foundations are exposed to very wet soil (high groundwater or flood zones).

Identify the problem, in order to avoid a French drain flood

The condition of the drain can be checked using a video camera connected to a monitor. For the camera to penetrate inside the drainage pipe, the drain must include external access points (cleaning openings) or be connected to a sump or storm sewer with a check valve. In addition, there should not be too many elbows in the system.

If a camera cannot be inserted into the drain pipe, the solution is excavation. This method is obviously more intrusive, but the advantage is that it allows an evaluation of the entire system, from the outside as well as from the inside.

Preparations for the operation

If only one part of the French drain is blocked, it is possible to restore it. A partial repair or replacement may also be sufficient, for example, on only one side of the building. In this case, the total cost may be only a few hundred dollars.

If the entire system needs to be replaced, the amount of your bill will go up, which can cost you between $10,000 and $15,000, or even more. In such a case, it is essential to obtain a detailed quote from companies specializing in French drain installation that hold a valid permit from the Régie du bâtiment du Québec that complies with the standards in force.

Is your basement damp or flooded?

If you see signs of water infiltration in your basement, consult a professional to have it checked. Getting your French drain repaired before the foundation damage manifests itself will save you a ton of grief and mold-related issues in the long run.