How much is the ground required to slope away from a house?
Saturday, June 30, 2018
The minimum drainage slope of the ground around a home is 6 inches of drop in the first 10 feet away from the home, according to the International Residential Code (IRC) and the Florida Building Code (FBC - R401.3), and this applies to all sides of the home. Where the house is closer to the property line than 10 feet, or walls or other barriers prevent compliance, drains or swales should be constructed to ensure adequate drainage away from the house. Impervious surfaces within 10 feet of the home, such as a driveway, are required to be sloped a minimum of 2 percent away from the house, which equals approximately 1/4 inch per foot.
Draining rainwater away from the home is important to protect your home’s foundation. Although a new home gets inspected by the local building department to be sure it meets these requirements, we often see older homes in which the homeowner’s landscaping has mounded soil that unintentionally reversed the slope of the ground towards the home. This seems to happen most often at inside corners of exterior walls, a place where a lot of water is running off the valley between two intersecting slopes of the roof above—exactly where it is most important keep water from ponding near the foundation.
Also, see our blog post How do I look for yard drainage problems when buying a house?
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