A flooded basement is definitely not a pleasant experience for homeowners, and as a result, a number of methods have been developed in an effort to prevent flooding. One such option for preventing basement flooding is the installation of an interior French drain. A countless number of basements have been retrofitted with French drains due to their relative low cost and the consistent, reliable flood control they provide. However, it's important to understand a few factors that will make a French drain installation the best it can possibly be; below is what you should know if you are considering installing a French drain in your basement:
Drain pipe material choices
A French drains contains pipe, known as "tile", that collect water and carries it to a sump. In most circumstances, a four or six-inch diameter pipe is suitable for use in a residential interior French drain, though you are likely to find other sizes in-use. There are several options to choose from when it comes to drain pipe materials and types, though the most popular choices are made from polyvinylchloride (PVC) and high-density polyethylene (HDPE). Below is an explanation of each type of pipe and a few advantages each can offer:
- PVC pipe – this type of pipe is commonly used in a variety of plumbing applications, including water supply lines and sewer lines. Installed in a French drain, PVC pipe is structurally-strong, fast-flowing and can be cleaned with rotary plumbing tools. In addition, PVC pipe is easily worked by hand, and there are numerous fittings commercially available for making simple "fit and cement" connections.
- HDPE pipe – specifically designed for use in drainage applications, HDPE pipe is usually sold in corrugated, flexible sections. It can be purchased with pre-drilled drain holes, and its flexibility allows it to be readily conformed to various curvatures and slopes without the need to use fittings. In addition, HDPE pipe is less expensive per-foot than PVC, so it is an affordable option for most homeowners.
Foundation design and construction
Most homes with a basement are built upon a foundation that rests upon a separate concrete footer. In this instance, the footer also supports the vertical walls. However, some foundations are poured as part of a one-piece (monolithic) construction process. That means the concrete floor of the basement also serves as a footer for the walls.
If your home's foundation is monolithic, then you need to be cautious when installing an interior French drain; breaking through the basement floor for the purpose of installing a trench may create a structural breach. Such a breach could significantly weaken and damage your home's structure. Always consult with an architect or engineer before breaking through a monolithic floor to see if it is safe or if you need to explore other alternatives for drainage.
While not strictly necessary, a flange that directs moisture pushing through the basement walls can contribute to a well-functioning French drain. Flanges are installed next to the basement walls, and they are either integrated with a specially-designed drain tile or added to the overall system. Flanges eliminate the concern about water failing to reach the drain tile and pooling and stagnating behind or beneath the tile.
Filtering and aggregate choices
A French drain rests within a bed of some type of aggregate material, usually gravel, that serves to support and protect the pipe. In addition, the gravel serves as a filter for trapping soil and sand particles that work their way into the basement through seepage.
An inappropriately sized gravel can lessen the effectiveness of a French drain; if the gravel is too large, the water will not be adequately filtered as it works its way toward the drain tile. Conversely, gravel that is too small will become clogged with particles, and it could prevent the water from draining properly, if at all. No one gravel size is best for every situation, so you will want to discuss your options with a qualified installer who can help you make an informed decision.\
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