Grading Around a Foundation

The establishment and maintenance of proper grading around a foundation are essential. Drainage problems around a foundation can be due to the grading not being adequate at the time of construction, site changes by the owner, or maintenance problems.

Flat grading (less than 5% slope) prevents water from properly flowing away from the foundation and allows water to seep into the foundation backfill material, resulting in the settlement of the backfill. In addition, water can affect soil that is sensitive to wetting leading to foundation damage

The grading at the front of these townhomes is too flat. The area around the foundation should drop down 12” in the first 10 feet. This problem is attributed to site grading (elevations) that did not match the engineer’s design.

The optimum slope away from a foundation is 12 inches vertical drop for the first 10 feet (10%). In cases where ten feet of distance is not available, for example, where houses are very close together, 6 inches vertical drop for the first 5 feet (5%) may be used.

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The Foundation "Protective Zone"

Engineers refer to the 10 feet around a foundation as the "protective zone." The industry standards and criteria dictate that precautions are taken during the design and construction of grading in this "protective zone " to ensure proper drainage.

The slope around a foundation must be steep enough to quickly divert water away from the foundation.

Sideyard with adequate ground slope and gutter extensions properly installed to divert water away from the window wells and foundation.

Backfill around the foundation may settle and should be repaired to establish a proper slope around the foundation.

Low spots on the ground surface around a foundation collect water and allow it to infiltrate into the foundation backfill, which can result in soil problems and foundation movement.

Example of a drainage low point at the foundation.

The ground around a foundation should be properly sloped and divert water to a swale that carries the water to downstream storm sewer infrastructure.

Foundation backfill that has settled and drainage low points in the ground surface around a foundation need to be repaired to standards per the Building Code.

Per the Residential Building Code (IRC) - Section R401.3-Drainage, where lines, walls, slopes, or other physical barriers prohibit 6 inches of fall within 10 feet, drains or swales shall be constructed to ensure drainage away from the structure. Impervious surfaces within 10 feet of the building foundation shall be sloped a minimum of 2 percent away from the building.

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I hope this information was helpful to you. For additional topics related to construction defects, go to SiteDamage.com.

Visit my photo collections page, which has examples of damage that can be due to construction defects.  

Mike's Photo Collections

Mike

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Additional Resources

• Foundations 

• Drainage

• Soil 

• Erosion

• Concrete Flatwork

• Asphalt Pavement

• Concrete Pavement

• Masonry Pavement 

• Retaining Walls