The number one concern I receive in my pre-inspection interviews relate to foundation movement. There are many factors that can affect a solid foundation. Expansive soils and foundation design are two of the most critical. However there is one common suggestion amoung both design professionals and soils experts that play a vital role in maintaining a healthy stable home.

Drainage.

Poor surface and subsurface drainage can lead to water ponding around your home, leaks in your basement and water seeping into your crawlspace.  Successful drainage requires leading surface water away from the outside foundation wall at the appropriate angle.  What is the correct angle?

According to standard building practices the grade immediately adjacent to the building should be sloped a minimum of 5% (or 3 inches every 5 feet) for at least 10 feet outward from a building foundation or as far as practical. Here is how to measure the slope.

Slope is the ratio of the length of the rise (the vertical change) to the length of the run (the horizontal change). A simple way to measure slope is to use a carpenter’s level placed on a 2×4.

Place the board on the ground along the slope you want to measure and lift the lower end until the board is level.

To determine the rise, measure the distance from the ground to the bottom edge of the board.

The run is the length of the board from the end to where you measured the rise.

Divide the rise by the run to obtain the per cent of the slope. For example, if the rise is 3 inches and the run is 60 inches, the slope is 3 ÷ 60 = 5%.

This entry was posted on Saturday, February 16th, 2008 at 11:09 am and is filed under Foundations. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.