How to Properly Install a French Drain
Step 1: Locate the Problem
Locate where the water issues are and a viable exit. Before installing any drainage system make sure you can't solve the problem with gravel, extra dirt, or a basic trench.
Once the problem area is located, scout out a viable path where you can move the water. You will want to move the water away from any structure and be aware of possible erosion at the exit point.
Step 2: Get Approval
Before moving forward be sure the drain will not adversely affect any neighboring properties, as well as check up with your city and county laws for permitting laws. Once approved call 811 to mark off any underground utilities.
Step 3: Check the Slope
In order for the water to properly drain you will need a slope of at least a 1% (1 foot down per 100 feet). If the property does not have a natural slope you will have to dig the trench to be sloped.
In order to check the natural slope, drive a stake into the ground on each end of where the drain will be and then attach a line level.
If the property has no natural slope and the exit point is higher or level to where the drain is going you have a few options; either lead the french drain into a dry well and end it there or lead the drain into a dry well and insert a sump pump to remove the water on the positive slope.
Step 4: Get the Supplies
Once you have come up with a plan order your supplies. You will need to figure out how many feet of piping you will need and whether or not you will be using corrugated piping or PVC piping. You will want to use Perforated piping (piping with holes in it.) Corrugated piping typically comes in 10', 25', 50', and 100' pieces while PVC piping will come in 10' sections. Make sure to calculate how many fittings you will need and we recommend you buy a few extra. Then calculate how much gravel you will need. You will need to surround the entire pipe with 2" of gravel (piping is typically 4"). Finally you will need to buy a high quality landscape fabric to encase the entire pipe and the gravel.
Also decide if you are going to use any solid piping, sometimes the french drain covers a certain area and then you can use a solid pipe to move the water over a further area.
Step 5: Dig the Trench and Install the Drain
For a 4" pipe you will want to dig the trench 8" wide and 10-12" deep for anywhere the french drain is going. For just solid piping you only need the trench the width of the pipe. Once the trench is dug check the slope by using the stake and line method or pour water in it and see if it reaches the point you want the water to exit. Once the slope is correct lay the landscape fabric with 2" of gravel and spread evenly. Then lay the perforated pipe holes down and check the slope one last time. Finish the drainage system by filling the rest of the trench with gravel 2" all around leaving 2-4" left on top. Fold over the landscape fabric to completely encase the pipe and gravel and then fill the the remainder with soil, mulch, sod, or seed with soil.
Step 5: Enjoy your Dry Area!