What Is the Best Way to Grade the Ground away from a House?

Lot Grading Issues

• The main principle of lot grading is positive drainage, which means that water should flow away from structures. Soil and compaction are key components to achieving positive surface drainage. A slope of 2 percent -- 2 feet of drop in 100 feet -- will drain water, but building regulations usually require a steeper grade close to the house. Another concern is discharge. Some municipalities require runoff to be handled on the property, while others permit discharge into the municipal system.

Surface Drainage

• A slope of at least 5 percent -- a 6-inch drop over 10 feet -- is usually required for a certain distance from the foundation, typically 5 or 10 feet. This results in an apron around the house, slightly raised from the surrounding ground. Surface drainage is directed toward swales, or shallow depressions, in the side yards to channel water toward a municipal drain or open area, such as a lawn or field.

Soil and Compaction

• Soil movement caused by water in the soil leads to settling around the foundation and concrete cracks. Soft soil and organic matter should be removed and replaced with well-draining gravel. The gravel is placed in 6-inch layers and compacted to prevent settling, using a vibrating plate compactor or similar equipment. The ground needs to be at least 8 inches below the top of the foundation wall

Areas of Concern

• Adjacent property shouldn't be impacted by lot grading. The swales in the side yards are critical to ensuring drainage is captured before it leaves your property; they need to be at least 6 inches deep. Downspouts are potential causes of erosion around the foundation that can lead to flooding and other problems. They should be placed so that they discharge at least 3 feet from the foundation toward the swales, or they can be connected to an underground drainage channel.