Reviewed by Mike Sutton
Updated April 13, 2023
You’ve got all kinds of drains in your house: every sink and every tub has a drain, plus the one that’s probably next to your washing machine.
But did you know that there is a very important drain located outside your home? This is known as your perimeter drain or weeping tile system. If your perimeter system isn’t operating properly, you’ll end up with a wet basement or crawl space.
Here, we’ll explain what perimeter drains systems are, how they work, and what homeowners should know about them.
A perimeter drain is something that all houses have, and it is designed to prevent water from seeping into your basement. It is intended to attract water in the soil that has either accumulated from heavy rains, melting snow, or from rising groundwater. It then carries the water away from your house, so it is less likely to seep in through your basement walls.
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.
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.
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.
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.
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.
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.
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:
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Perimeter drains are underground, out of sight and out of mind. Many homeowners don’t even think about them until something goes wrong.
However, you should have an inspection done periodically, especially if you’ve noticed water stains on your basement walls or pooling water near your foundation, as mentioned above. You can hire an inspection company to stick a camera into the perimeter drain, to see if it’s functioning properly or identify blockages.
Sometimes cleaning may be all that is necessary, rather than a repair or total replacement.
Unfortunately, aging systems may be beyond simple maintenance; you may need to replace them with a modern, well-built perimeter drain system.
“Using quality materials is, first and foremost, our biggest tip,” says Sutton. “[We use] drainage tiles with more holes per linear foot, [and] we line the trench with non-woven geotextile fabric. This allows the water to get through to the pipe openings and keep dirt from entering the pipe.
“We only use a sock when the stone is crushed stone, which can create smaller rock fines that end up blocking the holes that allow water to seep into the pipe.”
Installing a new system with the right materials and design will make future maintenance a lot easer. For the most part, you’ll only need to periodically clean it out. If your system is designed right, you’ll be able to clean it out yourself.
“Having a clean-out access is one way to make sure you can flush the line with either high pressure water line or garden hose,” says Sutton.
Insurance companies will want to know if you have had any water in your basement. They may also ask about the condition of your foundation. A cracked foundation puts your basement at serious risk of water damage, and of course, damage by mould if the water damage isn’t addressed right away. Making sure your perimeter drain is working properly is one of the many things you can do to help waterproof your basement.
Some home insurance policies cover certain types of flooding. But, be sure to read your policy or talk to your insurance agent to fully understand what types of water damage are covered and what types are not.
Some policies cover rising ground water, while some won’t. Seeping of water into the basement is almost never covered by insurance, so it is even more important for you to take the proper steps to prevent it.
Removal of mould is another cost that is not normally covered by home insurance. The cost to clean up the resulting mess and make any necessary repairs will be coming out of your own pocket.
Accordingly, you may want to spend some money now to make sure your perimeter drainage system is in good repair and is working properly. Or, you could be facing even larger expenses later to repair any water damage to your home, as well as damage to property in your basement, that is not covered by home insurance.
Ultimately, though, the cost to maintain a working perimeter drain system is much less than the damage that can result from a broken system.
Always get a home insurance policy which provides the broadest form of water damage coverage possible, and be sure you know what is covered and what is excluded before anything happens.
Perimeter drains or weeping tiles can last for decades.
If properly installed, you can expect to have a problem free basement for a very long time. Older clay weeping tiles tended to deteriorate, and become clogged with soil and tree roots, but even these systems lasted for many years.
With modern materials, you can expect an even longer lifespan for your perimeter drain system.
The cost of installing a new perimeter drain system varies, obviously. The volume of soil that needs to be moved is one major factor. The quantity (and quality) of the materials are also important. Plus, there’s the cost of labour—installing a perimeter drain system is a time consuming process, one that most homeowner’s aren’t equipped to do themselves.
“A rough estimate is $65-$80 per linear foot, which will include all labour, materials, and soil removal,” says Sutton.
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About the expert: Mike Sutton
Mike Sutton is the owner of French Drain Man Canada, which has been building de-watering systems in Canada since 2019 for both residential and commercial builds. FDM Canada is the distributor of French Drain Man Products manufactured in the US, designed to move water quickly and efficiently.
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