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Question DetailsAsked on 6/8/2015

How much should french drain installation cost?

we have two low areas in our backyard from several years of hard downpours where a tree roots are not allowing the water to drain properly and water continues to accumulate where now the water levels are getting too HIGH and close to our back door.

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1 Answer


A french drain would be almost a last resort - generally, for a low-maintenance and weather-proof solution, you are better off filling (berming if necessary) from the foundation (leaving 4+" clearance from top of foundation wall AND from bottom of siding) or excavating a swale in the yard to drain.

You started off saying 2 low areas, but then said water levels are getting too high and close to back door, so unless the area buy the back door is low and can be filled (like with 3/4" minus crushed stone) without getting near top of foundation level, it is really a case of the surrounding grade being too high relative to the house, so a drainage swale sounds like the solution, to connect the low spots and drain away from the house. At the major tree roots, to protect them, you can use a hose with jet nozzle to tunnel under the roots to connect the swales on each side, putting in a piece of culvert or several pieces of side-by-side drain pipe (depending on amount of water to be handled) to go under the root while still keeping it covered with dirt to protect it. Using staggered flat patio pavers to make one or more openings for water to flow through also works, as do CMU's (concrete foundation blocks) on side to so openings line up.

If you go with fill near the house to keep the water away, it needs to be from typically 3-6 feet wide (border width around house) with the wider dimension if your natural soil is fairly permeable, should be compacted and not free-draining material so it does not act as a big sponge, and of course should drain away from the house at a slope of at least 2% and preferably 5% or more, and NOT trap water against the house. Preferably, both the surface you place it on and the finish grade should slope away from the house to minimize the amount of rainfall that soaks into the ground near the foundation.

Contractor for relatively minor fill, regrading, swale, etc would be a Landscaping contractor. Excavation if talking many, many truckloads of material or many feet of excavation. Of course, don't forget utility locates before digging.

Answered 4 years ago by LCD

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