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Getting Your French Drain Right The First Time


by Gabby Hyman
Repair-Home Columnist

Mon ami, French drains have nothing to do with a European country. They were devised by Massachusetts resident Henry French in 1859 as a means of routing surface water away from farm structures. Regardless of your heritage, or the historical lineage of your home, you should know that French drains--installed properly--are a sound way of protecting your basement and foundation from water damage.

According to National Building Inspectors, poor drainage accounts for between 80 and 90 percent of all home foundation woes. Free-standing water can also encourage mold and wood rot. If your downspouts aim at your outside walls, or if your soils don't naturally slope away from your dwelling, a French drain may be the easiest way of preventing seepage. French drains are simply trenches filled with rocks (many prefer lava rocks), gravel, and perforated piping.

French drain installations make a prudent home improvement project and can be installed by homeowners, but if you're baffled by the process you may want to call in a home or landscape contractor. Your biggest expense will typically be contracting for digging labor. The trench should go in at least two feet below your substructure soil level. Digging the trench too close to the house can complicate your problems.

A good rule of thumb is moving the drain one foot off the wall for each foot down you dig; for a four-foot deep drain, build it four feet from your walls. You'll need at least a 1 percent grade or the drain will become a French pond. The piping must terminate at a lower point than where the pooling water source originates or the entire gravity-feed theory won't work.

French Drain Piping and Fabric

Original French drain designs had their problems with clogging with sand and silt. That's why many contractors recommend using slotted pipes with the perforations or slots facing downwards. The perforations are large enough to pass minute sand particles and keep things moving.

Four-inch slotted PVC or plastic pipe can do the trick. You should cover the pipe with filter fabric or landscapers cloth (between your gravel and soil) to protect your pipes from clogging. The fabric or cloth will absolutely extend the life of your French drain. Be sure to lay in at least a foot of washed gravel above the piping before you backfill the trench.

About the Author
Gabby Hyman has created online strategies and written content for Fortune 500 companies including eToys, GoTo.com, Siebel Systems, Microsoft Encarta, Avaya, and Nissan UK.