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FRENCH DRAINS: INSTALLATION AND BENEFITS

What exactly is a french drain and how it can help to keep my foundation safe? Those and many more questions regarding french drains will be explored today.


As the name clearly states it, a french drain is a type of drain installed on a home’s exterior, that helps prevent water from entering the house and therefore damaging the foundation. Known by alternate names like filter drain, trench drain and rubble drain, this system consists of a trench that is dug around the perimeter of your house. A perforated pipe is then put at the bottom of the trench. This pipe, which is generally made of PVC, has small holes along its length to allow water to enter. The pipe is then covered by a layer of gravel, which allows water to flow easily. A filter fabric is placed on top of the gravel to prevent fine particles of soul from clogging the gravel and pipe.





Then the trench is backfilled with soil, covering the aforementioned fabric. This backfill must slope away from the foundation and towards a designated drainage point, ensuring that water will flow away from the foundation. 


Once the rains start and rainwater accumulates around the foundation and soil, it seeps into the french drain through the gravel and perforated pipe, then flowing along the pipe and away from the foundation and preventing it from impacting the soil beneath the foundation. Remember that water and moisture are some of the worst enemies of a foundation, so the best we keep them at bay, the better.


One of the good things about french drain is that they can be of great help to both slab on grade and pier and beam foundations alike. For concrete slab foundations it will help prevent cracks as it will minimize hydrostatic pressure from being placed on the slab, as well as eliminating heaving as excess water could also force the slab foundation upwards. In the case of pier and beam foundations, the french drain can avoid water damage in crawlspaces. By stopping water from pooling, you will be effectively fighting rot and mold. And by keeping excess moisture at bay you protect your floors from sagging and squeaking.


Besides from being effective to prevent accumulation of water from entering your home and its structure they can also control soil erosion effectively and when done correctly they can last up to 30 years. And besides, if taken into account when landscaping, it can provide an interesting and beautiful visual than can enhance your green spaces.


Now, let’s say that you are convinced. You want to install a french drain. There are certain mistakes that you have to avoid at all costs when installing a french drain. And the first one is not taking into account utility lines. Ignoring something so simple can bring about so many problems. It is vital to determine where the utility lines are running before starting to dig. Not only you can cause damages that will be costly to repair, but it could also prove quite dangerous if you hit any gas or power lines. So the best thing to do here is to call utility companies as well as regional authorities before proceeding. They can give you the necessary guidance on how to proceed with digging the trenches as well as alternative methods and solutions to work around installed utility lines.


Pipes for french drainage are meant to be perforated, so water can filter through. These perforations will draw water away from your home and to the designated place where it will be dispersed. When placing the pipes you have to make sure that the perforations are pointing downwards as, with the help of gravity, this will provide the best drainage possible.


During the installation process it is imperative to perfectly line the trench with the drainage fabric. This fabric will separate debris and dirt from mixing and allowing water to flow freely down the trench. It will also act as a filter, will help prevent weeds and roots from growing into the drain and stabilizing the soil around the drain to prevent erosion. If you fail to perfectly line the trench with the fabric then all of this will fail.


But is not only a matter of lining up the fabric, but of choosing the right type of fabric as well. Woven geotextiles are fabrics made out of synthetic fibers that are woven to create a durable, porous material that is excellent for soil separation and filtration. Then there are non-woven geotextiles that are made by bonding or needle-punching synthetic fibers together. They pretty much serve the same function as the woven geotextiles. There are also other fabrics that are made exclusively for drainage applications. These are manufactured to allow efficient water flow while preventing soil from intruding into the drainage systems.


Another mistake that is relatively common to find in french drain installations is a a lack of a positive drain slope. A drain pipe needs to be set at an angle so that water will flow and drain properly. A positive slope ensures gravity will do its job and naturally distribute rain water to the drain lines. Without a slope the water will not drain and will cause pooling, which in turn can attract tree roots that will block the water, negating the purpose of the system itself. And a negative slope will simply make it impossible for water to flow. At all.


Using an incorrect drain rock type will also defeat the purpose of your french drains. Clean, natural rounds stones are the best for this as they allow water to flow better. This gravel layer serves as the main waterway to prevent pooling. Avoid pea gravel, as it creates slower flow rates due to its smaller size. Also, avoid crushed rock which might clog the inlets. The bigger gravel, the better the flow of water. Typically half an inch to one inch across this gravel will also prevent blockages. Remember, rocks that are smooth to the touch are the best for french drains.


One very important tip is that the french drain should be installed below the frost line as this will ensure optimal performance throughout the entire year, as snow and freezing temperatures will not be able to cause obstructions that freezing/thawing cycles could bring about.


You must also keep in mind that french drains are not made for catching water coming down the gutters as this can lead to it getting clogged up with debris, so for this we recommend installing a catch basin for better rainwater management, helping catch leaves and debris coming from the gutters, preventing them from entering the french drain and clogging it.





Now, what of the mounds of excavated soil that you have laying around now that the french drain has been installed? Well, whatever you do, do not return the soil to the excavated area. The whole point of the drain is that the ground was not draining properly and putting the soil back can cause the system to clog. 


Having explained what french drains are, how they work and how they help keep your foundation safe, remember that the best way to achieve the best results when installing these systems is by calling us, your seasoned professionals. We will make sure to plan your french drainage system carefully, choosing the best and most suitable materials, and always using the quality and commitment to our job that have been iFix’s defining trait since our conception.

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