French drain with drainpipe. (Courtesy: Pioneer International at flickr.com)
In previous articles I have discussed the problem of poor drainage and discussed in general terms what you
French Drain with pipe and landscape fabric. (Courtesy: Kllisk at flickr.com)
can do to alleviate the problem. Alternatives that were discussed included the creation of a rain garden or a French drain system.
I have discussed in more detail the creation of a rain garden. In this article I will discuss the construction of a French drain system.
What is a French Drain?
Before going into any detail concerning the planning and construction of a French drain system, there should be a definition of what a French drain system is.
A French Drain System is a small downward sloping ditch filled with rocks or gravel and a PVC pipe that channels water from a location where you don’t want it to another location where you do.
The drain includes:
· A trench of about 12-inches wide and 18-inches to 24-inches deep.
· A 4-inch diameter perforated plastic drainpipe.
· Washed drainage gravel.
· Porous landscape fabric.
There is an online website that offers a calculator that will assist you in determining how much gravel should be used in your particular drain. The drainpipe is necessary to collect the extra water. The landscape fabric is present to prevent silt and roots from entering into the drainpipe.
Planning a French Drain
Although constructing a French drain is not a difficult undertaking, it is imperative that you plan out the project before starting.
The first thing you need to do is check with the local authorities to find out if you need a permit to perform excavation work on your property. In addition, call DigSafe (888-DIG-SAFE (344-7233) and ask the local utility company to send out a representative to mark the route of their facilities on your property.
Next, determine the best place to locate the drain. The concept of a French drain is to catch the excess water at a high point and channel it to a lower point. So consider an area of your lawn that follows this topography. Experts say that the drain needs a down slope of 1 percent.
Some measuring may have to be done to assure that the location you select has that 1 percent slope. You could hire a surveyor to confirm this or you can do it yourself using two wooden stakes, a line level and twine and perform the measurement as follows:
1. Drive one stake into your lawn where the top end of the drain will be and tie the string to it.
2. Place a stake where the bottom end of the drain will be and loosely tie the string to it.
3. Use the level to level the string. Adjust the string as necessary to achieve proper level. Once level is achieved, tie the string tightly.
4. Measure the slope. The drain should slope one foot for every 100 feet of its length. Once set, move the string on the slower stake the proper amount and it will then serve as a guide for the proper grade.
Experts who have constructed such ditches advise that you also consider putting the trench along the edge of your property where digging would be relatively easy. Make sure that the route of the trench does not run through an area of the lawn that is often used by members of the family or where it might affect a planned home improvement.
Constructing the French Drain System
French Drain with gravel. (Courtesy: Jon Haupt at flickr.com)
Now comes the most demanding part of the project –- constructing the drain. Obviously, a hole needs to be dug. You can dig it yourself using a shovel; you can rent a trenching tool, which is a walk-behind trenching machine that can be used to cut up to 18-inches deep and 24-inches wide; or you can hire a backhoe and operator, who can dig a deep and wide trench quickly. Cost of renting a trenching tool is about $125 to $200 a day. Cost of hiring a backhoe and operator ranges from $300 to $1,500.
Here are instructions for constructing the drain:
· Dig the trench.
· Line the trench with the landscape fabric. The fabric needs to be wide enough to extend beyond the top of the trench about one-foot on both sides. Temporarily pin the extra fabric in place with nails or landscape fabric pins.
· Pour two to three-inches of gravel into the trench.
· Lay the drainpipe with the drain holes facing down.
· Cover the drainpipe with gravel up to the top of the trench.
· Fold the extra landscape fabric over the gravel.
· Lay soil over the fabric and apply grass seed or lay out sod.
