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Linear French Drain Illustration

By Tim Carter
©1993-2008 Tim Carter
Summary: Here is a diagram for installing French drain systems around your home. The linear French drain design is simple. The slope of the soil around the home is very important to keep in mind.

Related Terms:  French drains, French drain design, trench drain

! ! ! See Author's Notes at Bottom of Column ! ! !

 

 

 

 

 

 

 

 

 

 

 


Author's Notes:

You may wonder if my advice is worth anything. Well, read what Jim Sanders wrote to me when he was at the end of his rope:

"Hi, I just wanted to write to give you the results of my "Trench Drain". I have had a wet crawlspace for 15 years. Water would fill the crawlspace at times, so we actually had to drill weepholes at the base so that it would enter the basement and eventually, the sump pump.

I have tried everything. Several contractors said that the only thing we could do was to bring the water into the house via drainage tile and let it enter the sump pump. That would work, but because I live on a 6' elevation, there is no reason that I should have water problems. It became like clockwork...when it rained, we would rush home from the lake or wherever we were vacationing so that we could be prepared to start the backup generator, in case the power failed. We even had our alarm company put a sump alarm on our system, so they could notify us if we had a power failure. Battery backup was not an option, because sometimes we loose power for days and during any rain, our sump would run every 7 minutes...just like clockwork.

I found your site and read the article on the trench or French drain. At first, it sounded a bit like "holistic healing" to me. I failed to understand why a 2 ft. deep trench, 4 ft. away from the house would do any good. How could this simple thing correct an extreme water problem that has plagued me for years, cracked my foundation, settled my garage floor and ruined almost every vacation?

The Linear French Drain trench running from the house. PHOTO CREDIT: Jim Sanders
I decided "what the heck". I had to dig by hand using a trenching spade and a pick-axe, because the builder back-filled our property with brick and blacktop. It took quite a bit of time. Because the ground level varies so much on that side of the house, I was not able to achieve exactly 2 ft. deep. It varied from 18" to 30" in spots, but the slope was downhill. The trench is about 80 ft. long. At times, I thought about filling it all in, because I just didn’t believe that it would work.

I stoned it, put tile in, and filled it with #1 round stone. I socked the pipe just for safety measure and I also used geotext fabric on top, so I could cover with dirt and grass. I also ordered some clay and pitched from the house to the drain.

After a short rain, water is running away from the house. PHOTO CREDIT: Jim Sanders
Result? For the last month, we have had 7 or 8 torrential rains, the worst of which was last night. It rained so hard, that our lawn washed out in spots because of the high clay content. Our sump pump, that normally ran every 7 minutes during and after rain, has not turned on for 4 weeks. The silt at the bottom of the sump well is now dry and cracking. Our crawlspace has not shown a trace of water or even moisture.

Since I couldn’t see correcting the foundation cracks or the garage floor settling and tilting until I corrected the problem's source, I waited to see if the trench drain worked first.

This week, I had a company come in and perform sort of a "mud-jacking" technique on the garage floor, which worked perfectly. Also, during the past few weeks, I parged the cracks in the foundation.

A dry sump pump. PHOTO CREDIT: Jim Sanders
I just wanted you to know how this worked. I stressed for many years over this issue and the solution was nowhere near as difficult as I thought it would be.

As a side note, I went to the end of the drain tile during a hard rain to see what was happening. Water was running out of the drain tile in about the same exact volume that it previously ran out of the weepholes in my crawlspace. This winter will be interesting, because last year, the ground next to the house was so saturated that during a thaw, my sump would run constantly. I'm guessing that the ground between the trench and the house will probably be drier now going into this winter."

- Jim Sanders, Upstate area - New York







Comments

Ruben Loioco
27 Nov 2007, 13:18
I represent my client in buying this house with drainage problem in Los Angeles and I need to have an expert to answer few questions for me and my client, can you address me to someone to give us an estimate to resolve this problem please 310-642-7653 xt 128

Ruben
Jeffrey Ogno
04 May 2008, 13:34
My modular home sits on a full poured concrete basement. The 5 acre site is all bank run gravel. There is a stream 175 feet from the back of the house.
Two summers ago we had very bad rain, and the stream level was very high. That next morning our basement floor heaved up and split from one end to the other, allowing 5 feet of water to enter the basement. There was only puddles on the ground outside, this water came from under the home. The stream never overflowed. What kind of drainage can you recommend to overkill this problem and ensure it never happens again?
Thank you
Jeff
danny
19 May 2008, 16:37
When installing a french drain should the holes in the pipe be up or down. I have heard both ways.
Roger
20 May 2008, 09:00
Danny,

In Tim's column - http://www.askthebuilder.com/B175_Soil_Drainage_Solution_French_Drain_Syste ms.shtml - he states that the holes must be down. Check out the column for his reasoning.
Ruhi
01 Jun 2008, 11:08
How far the french drain should be positioned from the foundation walls? Would be OK to have it away, say 10-12 from the foundation as long as there is enough slope away from the house towards to drain? Thanks.

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