Storm Water Drainage

Poor drainage resulting in leaky basements often stems from having insufficient slope away from the foundation. To do land grading properly, you must first know how much slope you need 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’s 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’ll 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’ll need

  • String (at least 12 feet long)
  • 2 stakes, and something to pound them into the ground
  • String level
  • Tape measure

How Much 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’s 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’ll 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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