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Grading and Drainage Around a Slab Foundation

Grading and Drainage Around a Slab Foundation

Improper grades prevent water from flowing away from the foundation. Proper grading and drainage of the soil adjacent to the foundation can be critical to the performance of the foundation and to avoid water penetration problems. The ground adjacent to the foundation should be graded such that there is positive drainage away from the foundation wall. Surface drainage should be diverted to a storm sewer or other approved point of collection. Lots should be graded so as to drain surface water away from the foundation. The grade away from a foundation should fall a minimum of 6-inches within the first 10-feet.

Grade clearance - There should be at least a 4-inch slab exposure where masonry veneer is used and a minimum of 6-inches where non masonry siding is used. A grade clearance of at least 1" is needed at flatwork such as patios or porches.

Trees that are too close to your foundation can cause damage to the slab. At least here in southeast Texas where there is a great deal of gumbo clay soil. That soil is expansive and swells when it gets wet and shrinks when it gets to dry.

If a tree’s limbs reach to, or over the house, it is likely that it’s roots reach under the foundation. A tree or trees that draw water from under the slab will cause the soil to shrink and settle which will allow most foundations to settle and possibly crack.

Diagram courtesy of www.cesinspect.com 

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