What is a perimeter drain system?
A perimeter drain is a system designed to move excess water away from the foundation of a house. Perimeter drains collect ground and surface water, and carry it a safe distance away from the building, preventing it from seeping into the basement. All homes have perimeter drain systems; without them, water from heavy rains or melting snow would accumulate near the foundation, eventually seeping in and causing significant damage.
Perimeter drains are also known as weeping tiles or French drains. Though actual clay tiles were once used to divert water, the “tiles” name has stuck even though tiles are no longer used. Perforated pipes are much more common nowadays. The “French” designation comes from Henry French of Concord, Massachusetts, who popularized the drainage method in the 1800s.
How do perimeter drains work?
A perimeter drain includes a plastic or PVC perforated pipe installed underground, around the perimeter of the house.
The perforations consist of thousands of tiny holes or slits that allow water to enter the pipe, and drain away from the foundation. The pipe is often covered by a mesh permeable sock which helps to prevent soil from getting into the pipe.
It is then covered by layers of gravel of graduated sizes (largest close to the pipe, followed by smaller gravel), and finally backfilled with soil. The gravel allows water to flow towards the drainage pipe, without allowing dirt and debris to clog it up. The weeping tile slopes away from the home and carries the water towards the main sewer system.
When a house is constructed, a certain amount of dirt around the perimeter of the home is excavated. Once construction is finished, this dirt is put back into place, making it looser than the untouched soil next to it. Therefore, water runs more easily through this soil, which just happens to be right next to your basement or crawl space walls.
This is one of the reasons it’s so important to have a good perimeter drain to get that water away from your house. When the contractors finish installing a perimeter drainage system, they should firmly tamp the earth into place, and ensure that the soil slopes away from the house to improve drainage.
Proper sloping, in addition to properly functioning perimeter drains, is vital in preventing water seepage. Most experts recommend a downward slope, away from the foundation, of 6 to 15 centimetres over a distance of 3 metres.
But the drainage system itself needs to be sloped, too.
“We dig a French drain 14 inches wide by 14 inches deep,” says Mike Sutton of French Drain Man Canada. “When we build a system, we have a starting point which is higher in elevation, maybe 12 inches deep instead of 14 inches to create some slope. Gradually, we drop down to wherever the discharge point of the system is.
“Many people build systems with no discharge point and simply lay the pipe in the ground hoping for the ground to absorb the water eventually. That works over longer periods of time, yet can lead to issues when heavy rains and snowmelts occur.”
When a home is originally constructed, the builder is responsible for ensuring the proper grading is achieved and will need to pass an inspection by a surveyor for the municipality, province, or state. It then becomes the homeowner’s responsibility to maintain the proper grade. If you plant trees, lay new sod, or put in a pool, you could be changing the way water drains away from the home.
If you’ve unintentionally caused water to run towards your neighbour’s property, you could be facing a lawsuit and will be responsible for any expenses to correct the situation.
What should you do when something goes wrong?
Deteriorating tiles
Older homes sometimes have clay or concrete weeping tiles, which do tend to deteriorate, collapse, and become blocked with dirt and roots as they age. You may need to replace the whole system with modern plastic weeping tile, or in some cases, you can simply replace the damaged sections.
Blockage
If your perimeter drain system is plugged, you may be able to have the system flushed. A professional can dig access points around the basement walls to access the drain and clean it out. Some older drain pipes have ridges on the inside which make it impossible to clean. These would probably need to be replaced.
Think about replacements
Perimeter drains are usually installed with a layer of gravel placed on top of the system, before the dirt is filled back in. This usually serves to prevent clogging. However, if the system is clogged up (and flushing doesn’t work) there’s not much you can do besides having the pipes replaced.
Install a clean-out port
If you are replacing your system, consider having a clean-out port installed. This type of port can be accessed from the surface, so there is no digging up to worry about should the system need cleaning at some point in the future.
Disconnect from the sewer system
Some older homes were constructed with the perimeter drainage and weeping tile connected directly to the sewer system, which is not designed to handle large volumes of runoff. If your home’s weeping tile or perimeter drainage system is connected to the sewer, you may be at risk of contributing to an overload of the system, which can cause water backups. You may want to consider disconnecting your home’s drainage from the sewer system.
A couple of indicators of a drainage problem are:
- Water stains on your basement walls. These are an indication that something is wrong and could be followed by serious flooding if you don’t take action.
- Puddles close to your home’s foundation: This is often a sign that your yard is not properly sloped away from your home, or that your downspouts are not directing water from the roof far enough away.
