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Ask the Builder: Drain swampy yards and stop wet basements

June 4, 2022 Updated Sat., June 4, 2022 at 9:26 a.m.

Water flowing through the soil creates a swamp in the backyard of this home and many others in the neighborhood.  (Tribune News Service)
Water flowing through the soil creates a swamp in the backyard of this home and many others in the neighborhood. (Tribune News Service)
By Tim Carter Tribune Content Agency

Ande lives in Puyallup and reads my weekly column in her newspaper. She’s got a very common problem. In fact, tens of thousands of people suffer from it in places where there’s a lot of rainfall for many months during the year.

Ande’s backyard turns into a miniature Okefenokee Swamp when it rains. Her crawlspace also floods. She asked for my assistance in solving the problem. Fortunately, my college degree is in geology with a focus in hydrogeology – the study of groundwater.

Each spring, I receive hundreds of emails from homeowners who are suffering from water leaking into basements and crawlspaces. Most have soggy yards, as well. The good news is that in almost all cases, you can solve these problems with moderate effort and minimal expense if you can do most of the work yourself.

I do lots of phone coaching with homeowners, and in a majority of cases, the builder caused most of the problems. The three biggest pain points are:

• Roof water is dumped onto the ground next to the house.

• The ground has not been sloped away from the house foundation.

• The lot was improperly graded before the house was built, impeding drainage of surface water to the natural lowest spot.

You’d be surprised at the amount of water that falls onto the roof. If the footprint of your house’s roof is close to 1,600 square feet, a rainstorm that dumps 1 inch of rain will create just over 1,000 gallons of water falling off the roof.

The last thing you want to do is dump all this water onto splash blocks at the base of downspouts. This water needs to be piped to municipal storm sewers or the lowest part of your lot where water would have drained naturally before your home was built.

The soil that touches up against your home must slope away from the foundation. If your home was built on a mountain peak, by default all the water would slope down and away from each side of your foundation. You can achieve the same thing by making sure the top of your foundation walls are at least 18 inches higher than any ground within 10 feet of the foundation.

The building code suggests the slope of the ground should fall at least 6 inches in the first horizontal 10 feet away from the foundation. This is a minimum standard. More slope is better.

Once you have the ground sloping away from the foundation on all sides, you do what’s necessary to slope your yard so water flows to the lowest point of your lot. This takes care of all surface water. It’s now time to deal with the water flowing through the topsoil.

When it rains, water flows into the topsoil and occupies the space previously taken up by air. The water then is pulled by gravity down and then sideways. Many soils have a clay component, and as you go deeper into the soil, the denser the clay becomes. This is why in the Midwest, South and many other parts of the U.S., it’s easy to create a pond. The clay soil acts like a giant pottery bowl.

If you know that this subsurface water is moving downslope toward your home, you have to intercept it before it hits your foundation. You redirect this water around your home and send it on its way to the ocean. That’s where all water wants to end up if given the chance unless you live in the Great Basin in the Southwest or similar locations in the world.

The best way to intercept the subsurface water is to dig a 6-inch-wide trench about 24 inches deep. In most situations, this gets you into the dense clay subsoil. I like to put about 1 or 2 inches of clean rock in the bottom of the trench. This rock should be the size of large green grapes. Be sure there’s no sand in the rock or smaller pieces of rock.

I then put a perforated 4-inch pipe on this gravel and then fill the trench to the top with the same grape-sized gravel. Water flowing through the soil hits this gravel, immediately drops down and finds its way into the drain pipe.

The trench might be L- or U-shaped as it goes around your home looking for daylight. As the ground slopes away from your home, the drain pipe will eventually pop out of the ground if you keep the bottom of the trench level or have a very slight fall to the drain pipe of ⅛ inch per foot In wet periods, you’ll see enough water flow out of the pipe to fill a 5-gallon bucket in a minute or two.

Subscribe to Tim Carter’s free newsletter at askthebuilder.com. Carter now does livestreaming video at 1 p.m. weekdays at youtube.com/askthebuilder.

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