Water always flows downhill, and by the easiest route possible. That’s the basic concept behind a French drain, a slightly sloped trench filled with round gravel and a pipe that diverts water away from your house.
By the way, a little research established that the name, French Drain, doesn’t come from the country of origin. However, from a certain Henry French, a judge and farmer in Concord, Massachusetts USA, who promoted the idea in an 1859 book about farm drainage.
How a French Drain Works
French drains provide an easy channel for water to flow through. Water runs into a gravel-filled trench, then into perforated pipe at the bottom of the trench. Water travels freely through the pipe, which empties a safe distance from the house. The trench bottom should be sloped to the direction you want water to flow.
When You Need a French Drain
- · When you have a problem with surface water
- · If water is getting into your basement
- · If you’re behind a retaining wall on a hillside
If Your Problem is Surface Water
Install a shallow french drain. Also called a curtain drain, it extends horizontally across your property, directly uphill of the area you want to dry out. It intercepts water and channels it around the water affected area. This type of drain doesn’t have to be very deep. Where the drain passes through areas with trees or shrubs, switch to solid pipe (not perforated) to reduce the risk of roots growing into the piping and clogging it.
If Water is Getting Into Your Basement or foundation
Install a deep French drain. Also called a footing drain, it runs around the perimeter of the house at the footing level and intercepts water before it can enter your basement or foundation. It’s easy to install during house construction, but much more difficult and expensive to add later. If you have tall basement walls, you may have to dig down quite a ways to access your foundation footing. Also, there are probably landscaping, decks, and walkways that will have to be ripped out in order to install the drain, adding to the cost. If there’s not enough slope for your drain system to work, you may need to pipe the collected water to a sump in the basement, where a paddle pump can lift it and send it to a drain system.
Install an interior French drain. An interior French drain intercepts water as it enters your basement through your walls — it’s the surest method of keeping your basement dry and a better option when a footing drain is not possible. However, if you have a finished basement, you’ll have to work under interior walls in order to install the system.
A channel need to be cut around the perimeter of your basement floor, chip out the concrete, and install perforated pipe all the way around. The water flows to a collection tank or sump in the floor, and a paddle pump sends it out to the nearest drain. The channel is patched with a thin layer of concrete.
If You’re are behind a Retaining Wall on a Hillside
If you’re behind a retaining wall on a hillside, a French drain is a must, behind the first course of stones or blocks. Otherwise, water moving down the hill will build up behind the wall and undermine it. In Malta, most cases that I come across are a result of nonexistent French drain. The cheapest and best solution is to plan and carry out the works before building your dream home. The pipe should rest on the same compacted gravel base or concrete footing that supports the wall. To protect the drain from clogging with silt, drape geotextile across the base or footing and up the slope before adding the pipe and drain gravel. Near the top of the wall, fold the cloth over the top of the gravel, and top with several layers of washed aggregate.
The following videos show water build-up of a property behind a retaining wall.