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Proper Site Drainage for Residential Buildings

Many homeowners are unaware of how much slope (grade) is needed around a house foundation. This is an important issue, because if land grading is not done properly, runoff can be directed toward your foundation. This unwanted water can eventually compromise its integrity.

If the ground around your house is completely flat or, worse yet, slopes down toward the foundation, you could easily develop a drainage problem at some point (assuming that you do not already have one). So how can you determine if your home “makes the grade?”

How Much Slope Do You Need in Land Grading Near Foundations?

If you own a home, you may eventually find yourself having to do some land grading near your house’s foundation to correct drainage issues. Poor drainage resulting water pooling near the foundation often stems from having insufficient slope away from the foundation. To do land grading properly, you must first know how much slope you need to have away from the house foundation.

The consensus seems to be that a good slope to aim for when grading land extending out from a house foundation is about 6 inches for the first 10 feet (that translates to a “slope” of 5 percent). Many professionals grade land successfully using a lesser slope than that, but those who wish to be on the safe side err on in the direction of greater slope.

But how do you find the slope of a stretch of land, to begin with (so you will know if the slope needs to be adjusted)? Rather than boring you with a fancy formula with “x” and “y” in it, used to determine slope, let’s take more of a hands-on approach to land grading.

To find the slope away from your foundation, you will need:

  • Some string (at least 12 feet long)
  • 2 stakes (we will call them “A” and “B”), and something to pound them into the ground
  • A string level (that is, a type of level designed to fit on a piece of string)
  • A tape measure

Do You Already Have the Correct Slope?

Using the above supplies, take the following steps to determine if sufficient slope currently exists:

  1. Tie one end of the string loosely around stake A.
  2. Pound stake A into the ground right near your foundation
  3. Slide the string down stake A, so that it rests at ground level
  4. Tie the other end of the string loosely around stake B.
  5. Now measure out 10 feet down the slope from stake A, and pound stake B into the ground there (if there is excess string, just wrap it around stake B). The string between the stakes should be fairly taut, but still adjustable.
  6. Slide the string up or down stake B, so as to make it roughly level.
  7. Put the string level on the string, at about the mid-point between the stakes.
  8. Now adjust the string up or down on stake B, so as to make it exactly level.
  9. Measure the distance from the string on stake B to the ground. Is the measurement 6 inches or more?

Do You Need to Re-Grade the Land?

The slope measurement you just took will determine whether or not you need to re-grade this land:

  • If the measurement is 6 inches or more, you have a perfect slope — no need for land grading here.
  • If not, you will need to re-grade the land by adding fill near the foundation and tamping it down; after which you can check the new slope by repeating the steps above.
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