Q&A / 

Water Drainage Tips

DEAR TIM: Spring is here and so are the incessant heavy rains. I have several places near my house where water ponds. This can't be a good thing for my house, as I constantly am battling water in my basement and part of the house that has a crawlspace under it. My lot isn't really that flat, so I'm at a loss as to what's going on. Do I have to call a professional to solve this issue, or can I just add soil to fill in the low spots? What are my options? Marion R., Evansville, IN

DEAR MARION: While I don't have accurate statistics to support my feelings, I suspect you're in a vast majority of homeowners who have varying degrees of poor drainage issues on their land or near their homes. You're correct in assuming that ponding water is not a good thing for houses.

This standing water next to the building is unacceptable. It can cause many different problems. There are several ways to solve the problem. Photo Credit: Tim Carter

This standing water next to the building is unacceptable. It can cause many different problems. There are several ways to solve the problem. Photo Credit: Tim Carter

My college degree was in geology. I gravitated to two disciplines within geology: geomorphology and hydrogeology. Geomorph, as we students affectionately called it, is the study of the Earth's surface features. Hydrogeology is the study of ground or subsurface water, or at least that's what we focused on the three years I was a geology student.

If you think about the Earth on a very large scale and take into consideration gravity, you quickly discover that Mother Nature is doing her best to constantly carry all soil, rock, your house, your car, your possessions and you down and into the oceans. She's a very patient woman, but she's also got a split personality as her evil twin is constantly building mountains where two crustal plates crash into one another. This is why the Earth has dry land that we build upon.

What does all this have to do with the water at and around your home? Simple. If you could look at a topographic map of your lot before it was developed, and in many locations these old maps are available, you'd see that your lot was shaped differently than it is now.

Your builder, or possibly the subdivision developer, undoubtedly moved dirt on your lot to prepare it for building your home. This process disturbed the natural slope of your lot as virtually no undisturbed land is perfectly flat. Almost all land has some natural fall to it that's caused by natural erosion. When you do encounter marshy land, it's because of some temporary geomorphological process. Lakes are a great example. You can find marshes next to lakes. Realize that lakes are temporary geological features. Mother Nature is constantly trying to fill lakes in.

Adding soil to the low spots is usually not a good method to fix poor drainage problems. Ponding water on your lot tells me that you don't have low-slope culverts surrounding your house like a moat surrounds a castle. These depressions, or culverts, should have been created by the builder so surface water always flows around your house to the towards the lowest spot of land on your lot.

To provide great drainage around your home, you should always have the ground slope away from your home. The building code used to require that the ground should have 6 inches of fall in the first 10 feet of horizontal run away from your home. That can be confusing to some.

All it means is that within 10 feet of your foundation, the ground should slope at least 6 inches. This change in elevation could happen within a foot, meaning it would be a very visible slope very close to your foundation walls.

The builder should have then created an artificial channel around and away from your home that also has a slope to it. The water flowing away from your foundation would enter this channel and then flow, by gravity, completely around your home. There should never be any ponding in this shallow channel. A slope of at least 1/8 inch per foot is required. More slope is better if you can tolerate it on your lot.

Surface water is but one challenge around your home. You also need to deal with subsurface water that flows through the soil towards your foundation and crawlspace walls. You can capture and divert this subsurface water by digging a narrow trench in the center of the artificial channel around your home.

This channel should be about 2 feet deep and 6 inches wide. The bottom of the trench should be parallel with the top of the artificial channel until it gets around your home. The trench extends past your home towards the lowest point of your lot. Once the trench passes your house, the slope can be reduced so the pipe eventually pops out of the ground.

You install a 1 inch layer of rounded gravel that's the size of large acorns into the bottom of the trench. Perforated drain pipe is laid on this gravel. The entire trench is then filled with the rounded gravel. This system readily collects subsurface water before it attacks your home. Water will flow from the end of the drainpipe where it eventually breaks through the surface of the ground.

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Want a step-by-step procedure on installing a Linear French Drain? Tim's Linear French Drain Video Series DVD shows you how to keep your basement and crawl spaces dry. CLICK HERE or on the image below to order Tim's DVD.



9 Responses to Water Drainage Tips

  1. Useing the perforated. pipes do you put the holes on the bottom or top. In a heated discussion about this I say holes on top need an expert to get an answer.

    • You're wrong. Holes on the bottom. Your way the water has to build up nearly FOUR inches to get into the pipe! Plus, rounded gravel can easily CHOKE / CLOG the holes when the trench is backfilled.

  2. Dear Tim; Thank you for your. Quick response and I will have to admit to my husband those awful dreaded words, I was wrong, I sure do hate to eat crow lol again thanks. I definitely will use your website again.

  3. Hi Tim, when you say there needs to be a slope of 6" over 10ft, does that slope need to be soil only or can I use rock? In my case, there is a rock bed that extends two feet out from my house, which then turns to grass, but there is hardly any slope to any of it. So, I was hoping to add rock on top of the existing rock to create the recommended slope in the first two feet. I feel like that is too easy to be right, but am not sure! Thank you!

    • Janet, the rock doesn't count especially if water runs right through it and disappears! Grade refers to SOIL. The soil needs to slope DOWN a minimum of 6 inches in the first 10 feet away from your home. Most houses do NOT meet this requirement to their detriment.

  4. Hi Tim, thanks so much for the quick reply! That was the answer I was afraid of, but I wanted to know for sure before I went to all the extra work. ๐Ÿ™‚ thanks again. Great website!

  5. Hi Tim,

    I need advice building a storm drain system. I'm going to dig a trench and run PVC alongside of a long exterior wall where three downspouts deposit water at different points. I will connect those downspouts to the buried piping which will lead to a dry well away from the house. My question is this: if I'm afraid of non-downspout water (so, just rainfall) pooling in the same area, would it make sense to make that piping perforated and backfill with gravel in order to make a French drain? Or would that defeat the purpose of having the pipes serve as a channel to the dry well for the downspout water (would it would exit through the perforations rather than continue to the dry well)?

  6. Hi Tim. Love all the information from the blog. Very informative. Question in regards to external sump pump. We are building in area that has high water table. The builder has advised that we should install an external sump with a French drain before he starts on the footings and then the weeping tile would be installed after that. This is what he had to do with another home in the area after lengthy delays because of the groundwater and rain this spring. It seems a little redundant to me. I can see how it would help them dry out the area to do footings etc but not sure long term if that's something that's required. The French drain/external sump is apparently my cost and a significant one at that. Any insight would be appreciated. Jeremy

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