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of Home Improvements

*French Drains*

How to build a French Drain outside your home

It's the water you can't see that can destroy your foundation. Pitch or tar used to waterproof exterior walls at the time of original construction often deteriorate in 3 to 5 years leaving the walls unprotected against the tremendous hydrostatic pressure of a high water table, underground streams or capillarity.

An excess of water around footings may undermine them causing damaging settlement of the foundation. If you have water puddling in your yard or areas that get washed out every time it rains you need to establish a drainage system. The simplest and most common is referred to as a French Drain. Getting the water to go where you wish is essential for improving yard drainage; the grade will facilitate your efforts. It is essentially a trench with a perforated pipe surrounded with gravel and pitched toward another part of your property. The ideal French drain leach field would be an out-of-the-way area with sandy soil, through which the water could seep into the ground harmlessly. Its not a difficult a project to figure out, its just a lot of digging.

Make yourself a plan

How are you going to dig your trench? You really don't want to dig it twice. Size of the trench will vary depending on your property, distance to travel, and pitch needed. Six to twelve inches wide should be plenty for most situations. Depth will be relative to your landscape and getting proper pitch. There must be enough pitch so that the water will flow in the right direction. While digging it's a good idea to keep checking to make sure you maintain the proper pitch.

Make sure that your trench will not disturb someone else property
Check with your local utility company before you start a digging operation. The ideal French drain leach field would be an out-of-the-way area with sandy soil, through which the water could seep into the ground harmlessly.

Getting the water to go where you wish is essential for improving yard drainage; the grade will facilitate your efforts.

Check yourself as you go.

For instance, if the trench for the French drain is to be 100' long and the grade 1%, then by the time your trench is 50' long, it should be 6" deeper than where you began excavating.

The digging is the most labor-intensive part of installing French drains. The trench will slope down toward the area where you've determined the water will be re-routed. Trench width will depend on the magnitude of your moisture problem. Bigger moisture problems call for wider trenches. Small trenches are often dug to a width of 5"- 6". Its better to have a trench that's too big than too small.

The Gravel Base

Before applying gravel, line the trench with landscape fabric to keep dirt out of the gravel.

Add a gravel base to the trench a couple inches thick. Insert a perforated drainpipe 4 to 6 inches in diameter, wrapped in a landscape filter fabric. It's a good idea to insert a few tees up to the surface in the event that you may have to clean out the pipe one day.

Fill the remainder of the trench with gravel to about 4 inches below grade. Cover the gravel with tarpaper and fill to grade with topsoil and seed. Gravel should be appox ¾ to 1 inch. Make sure that gravel surrounds all sides of the drainpipe.

I prefer to have the drainpipe connected to a drywell. The size would have to be determined by how much water you need to dispose of. A couple of cesspool rings is not uncommon. You may have to have someone install this for you. It's an additional expense but it's worth it, because it works.

French drain in the basement

A trench is dug around the perimeter of your basement next to the foundation walls the same way that the outside trench is dug. Twelve inches deep and twelve inches wide should be sufficient.

Start in 1 corner of the basement and pitch the pipe towards an opposite corner where the water will run into a sump pump pit. When water reaches a certain height in the pit it is automatically pumped out of the house.

Water pressure from a rising water table takes the path of least resistance. So it goes into the drain instead of your basement.

A small percentage of basement water problems are the result of underground water levels. When the water table rises above the level of the basement floor, the water is constantly applying pressure, trying to get in.

Serious basement water problems caused by high groundwater levels require serious prevention measures. Drains can be installed around the inside perimeter of the walls, and sump pumps can be installed to actively pump the water outside. These fixes may keep the house from floating away, but the presence of water in the basement, even as it is being drained or pumped away, is still going to raise the humidity in the air.

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