The first question to ask yourself is "Do I really need to build a french drain?". Water drainage in backyards is a common problem, especially in rainy climates like the Northwest. To add to my situation (I live in the Portland, Oregon area) my property is lower than my neighbors yard and therefore all his runoff comes straight into my backyard leaving me with excess water that literally has no were to go. The soil is very "clay" like and water does not drain very well leaving soggy lawns, muddy dirt, and an overflow of water that runs onto my back patio. A few years back I had a primary french drain installed to try and alleviate all the extra water that backed up in my yard and it worked, kind of. After a pretty wet winter/spring last year I had the same issues again with standing water and a very mossy lawn that were direct results from too much water not being able to flow out of my yard. A "french drain" is essentially a trench that gets dug along the most common route where the water is getting backed up. A pipe is laid down under the ground so the water can freely flow out of your yard and into the street or sewer system.
The biggest part of building a french drain is the labor involved with excavating the dirt/lawn that needs to be removed so that the piping can be laid down. The trench of a french drain is usually dug to about 12 to 18 inches in depth and about 6 inches wide (enough room to place the pipe). You need to start the trench where the source of the water is coming into your yard. Then plan the trench depth accordingly so that you can re-route the water. You want at least a 1% grade for french drains so that the mini-slope will carry the water down to it's final destination (the street/sewer). Once the trench is dug you will need to place a special pipe into the length of the hole so that water will escape along the pipe. The piping therefore need to have small holes in it so the water can eventually go into the pipe and out of the yard. The pipe should also be covered with a fabric material so that dirt and rocks can't get into it (only water). The pipe can be surrounded with gravel which will make water flow much easier and the top level above the french drain pipe can be gravel or larger rocks. We chose to put rocks the size of silver dollars on the top level of the french drain so that it aesthetically matched with other features in our yard. If you have a mossy lawn (even in summer months) or standing, muddy water in your yard, think about solving the problem by having a french drain installed. A french drain project can be done in a day if the area involved is no more than say 15-20 feet in length. The materials needed to build a french drain are a shovel, landscape fabric, gravel, carpenter's level, piping, and sand/rocks.
Cost of French Drain:
As we mentioned above, the labor involved with digging the actual trench is were most of your money will be spent unless you are willing to dig it yourself. If you choose to dig the trench, keep in mind that it needs to have that 1% grade or else the water will not flow downward and out of the yard properly. I decided to have the professional landscape team do my entire french drain system so the costs I took on are the full price it would cost from start to finish to build a french drain. I had 2 drains done within a years time so I can give you a good idea on pricing for different length french drains. The first drain measure 18 feet plus another 15 feet in my front yard to get the water out to the street and the total cost was $850. The last french drain that was built in my yard was measured at roughly 25' and cost $625. In both cases it worked out to about $25/foot of french drain that needed to be installed. Labor was the majority of the cost which means you could easily get the job done for much cheaper if you do the digging.
Waterproofing - Basement French Drain:
Plenty of homes have issues with water draining into their basements. The problem is usually gutter spouts that don't take water away from the homes foundation and instead let it buildup outside the base of the house until it slowly drains into the basement area. There is such a thing as a basement french drain in which a drain is placed along the wall where the water is getting in. You first need to get the walls of the basement assessed for water damage but if it's only the floor that is leaking water, then you can have a crew dig a drain along the base of the floor where it meets the wall and force water out of the area much like a french drain in your yard. The difficulty level involved in a basement french drain is much more than a traditional french drain so expect costs to be higher as well.
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