Get to know French drain systems


You have all kinds of drains in your house; all sinks and tubs have them, and there is likely a drain near your washer. But did you know that there is a very large drain outside your home? This is called your peripheral 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 all homes have and is designed to prevent water from entering your basement. It is intended to attract water to the soil that has accumulated as a result of heavy rain, snowmelt or the rise of groundwater. It then carries water away from your home, so it is less likely to seep through the walls of your basement. Many years ago, clay tiles were used to divert water, and the name weeping tile remained after that. Nowadays, perforated pipes are used in place of tiles. It is also sometimes called a French drain, because 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 house. Perforations consist of thousands of tiny holes or slits that allow water to enter the pipe and be drained away from the foundation of the house. The pipe is normally covered with a permeable membrane which prevents soil from entering the pipe. It is then covered with layers of graded cut gravel (the widest layers of gravel near the pipe, followed by smaller gravel) and is then backfilled with soil. The gravel allows water to flow to the drain hose, without letting dirt and debris clog it. The drainage slab is installed in such a way that it moves away from the house and transports the 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 construction is complete, this earth is put back in place, making it looser than the intact soil that adjoins the house. As a result, water flows more easily through this soil, which is right next to your basement or the crawlspace walls. This is one of the reasons why it is important to have a good perimeter drain to drain water from your home. Hopefully when the contractors have finished installing the perimeter drainage system, they have taken the time to properly pack the soil in place and make sure the soil tilts away from the house to improve drainage. Proper inclination, in addition to proper 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 owner’s responsibility to maintain the proper slope. If you are planting trees, laying new grass or installing a swimming pool, you could change the way water flows from the house. If you accidentally leak water to your neighbor’s property, you could be prosecuted and will be responsible for all costs incurred to correct the situation.

Be on the lookout for symptoms to avoid French Drain Flood


If your drain is not performing as it should, there will be signs, such as a much higher humidity level in the basement. This can even cause mold or rot on the floor and the bottom of the walls. On bare concrete surfaces, you may notice a whitish crystalline powder, a phenomenon known as efflorescence. Eventually, water will infiltrate into the basement between the footing and the base of the foundation walls or through the cracks in the concrete slab in the floor.

In the latter case, before concluding that the drain is defective, you must make sure that the water does not infiltrate for another reason. The problem may be, for example, a crack in the foundation wall or a defect in the building’s outer sheath (siding, windows, doors, balcony, etc.). To ensure this, it is usually enough to expose part of the basement wall. Another way is to wait for a dry spell and water the soil abundantly near the foundation.

The different problems and causes


Over time, French drains can be clogged with dirt, roots or other debris and will no longer be able to drain water from your home. If the drain is blocked, 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 have 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 tile, or in some cases you can simply replace the damaged sections.

If the tiles are blocked but have not sagged, the installation can be cleaned. A professional can dig access points around the walls of the basement to access and clean the drain. Some old drainage pipes have ridges inside which 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, failure is generally caused by improper installation (counter-slope, crushed pipe, insufficient fine gravel, etc.). In areas where the soil is rather sandy and ferrous, the drains can also be blocked by a reddish mud, ferrous ocher, if the foundations are exposed to very humid soil (high groundwater or floodable areas).

Identify the problem, to avoid a French Drain Flood


The drain status can be checked using a video camera connected to a monitor. For the camera to enter the drainage pipe, the drain must have external access points (cleaning openings) or be connected to a sump or a storm sewer with a non-return 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 whole system, from the outside as from the inside.

Preparation for the operation


If only one part of the French drain is blocked, it can be restored. A partial repair or replacement may also be sufficient, for example, on 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 on your bill will go up, possibly costing you between $ 10,000 and $ 15,000 or more. In such a case, it is essential to obtain a detailed quote from companies specializing in French drain installation who hold a valid permit from the Régie du bâtiment du Québec and comply with the standards in force.

Is your basement wet or flooded?


If you see signs of water infiltration in your basement, consult a professional to have it checked. Having your French drain repaired before damage to the foundation occurs will save you a ton of grief and long-term mold problems.