Ande lives in Puyallup and wrote to me with a very common problem. Many homeowners have to deal with it in places where there’s abundant rainfall for many months during the year.
When it rains, Ande’s backyard turns into a swamp and her crawl space floods.
Each spring, I receive hundreds of emails from readers who have water leaking into their basements and crawl spaces. Most have soggy yards as well.
You’d be surprised at the amount of water that falls onto your roof. If the footprint of your house is around 1,600 square feet, a rainstorm that dumps 1 inch of rain will create more than 1,000 gallons of water falling off the roof. This rainwater needs to be piped to municipal storm sewers or to the lowest part of your lot.
Problems like the ones Ande described are caused by three things:
• 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.
Any soil that touches your home must slope away from the foundation. If your home was built on a mountain peak, water would naturally flow away from each side of your foundation. You can achieve the same effect on a flat yard by making sure the top of your foundation walls are at least 18 inches higher than any ground within 10 feet of the foundation.
Most building codes suggest that the slope of the ground should fall at least 6 inches in the first 10 horizontal feet from the foundation. (This is a minimum standard; I think more slope is better.)
Once you have the ground sloping away from the foundation on all sides, it’s necessary to slope your yard so water flows to the lowest point of your lot. This will take care of the surface water. Then it’s 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 with air. Gravity then pulls the water down, then sideways.
If you find that this subsurface water is moving downhill toward your home, you need to intercept it before it makes it to your foundation and redirect it away from your home.
I believe the best way to intercept subsurface water is to dig a trench about 6 inches wide and 2 feet deep. I like to put about 1–2 inches of clean rocks in the bottom of the trench. These rock should be the size of large green grapes. Be sure you don’t include any sand or smaller pieces of rock.
Next, place a perforated 4-inch pipe on top of the gravel and fill the trench to the top with the same grape-sized gravel. When water flowing through the soil hits the gravel, it will drop down and finds its way into the drain pipe.
As the ground slopes away from your home, the drain pipe can eventually pop out of the ground. During rainy periods, you’ll see enough water flowing out of the pipe to fill a 5-gallon bucket in a minute or two — water that would otherwise be in your crawl space.
Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.