Sunday, August 7, 2011

French Drain

French drains are a time proven system for eliminating excess water. The earliest forms of French Drains were simple ditches, pitched from a high area to a lower one and filled with gravel. These were described and popularized by Henry French in his book Farm Drainage. Today, specialized drain tiles are designed with perforations or holes to admit water. To prevent clogging gravel is placed around the perimeter of the drain tile to give water a path to the drain tile as well as filter soil particles. With the development of geo-textile fabrics, gravel can now be surrounded with this fabric greatly enhancing its ability to filter soil. A French drain can be covered over with sod after installation, making them less conspicuous.

Over time the term French drain has developed numerous definitions and has been applied to many different products. It has gotten to the point that any piping that is buried in the ground is now called a French drain.

As explained in his book, Farm Drainage, "a trench is cut in the cellar-bottom, two feet from the wall, a foot deep at the farthest corner from the outlet and deepening towards it, round the whole cellar, following the course of the walls. In this trench, two-inch pipe tiles are laid, and carefully covered with tan-bark, and the trenches filled with the earth. This tile drain [is] connected with the outlet drain 18 inches under ground, and the earth levelled over the whole.”French Drains were originally designed for basements or cellars. The idea behind it was to decrease moisture which in turn improved air quality in the home. These are the same issues we have today and the same methods to solve these issues are used and approved by building codes.

With every simple design comes copy-cats looking to make a buck. Today the market is full of extruded plastic versions like “drain tracs”, “water conduits”, “drain guards” and the like. Many are trying to make a simple process more difficult, so that they can charge more money. Well sometimes a design works so well that we should stick with it. That is why building codes and engineers prefer simple perforated pipe surrounded with clean gravel and covered with geo-textile fabric. The only difficult part is the layout and the labor.

There are plenty of cautions and concerns when installing a French Drain system. One needs to be careful of its placement around footings in basement waterproofing applications. Too low can cause undermining of the footing and too high will not remove water from beneath the slab. Proper slob is also a large concern. Many companies try to cut costs by placing drain systems on top of footings. Once you realize that the foundation contractor went to great lengths to keep his footing flat, you will understand that water cannot run down hill if there is no hill. Be very careful of this type of modern day “french drain”.

French drains are very effective and time proven. When installed correctly and applied to correct situations they can handle vast quantities of water for many years.