The foundation grade is the slope of the land around a home's foundation. A properly established grade slopes away from the home and uses gravity to direct rainwater and snowmelt away from the foundation. Incorrect foundation grading can cause a host of problems, including swamp-like lawns, damp and leaking basements, even cracked foundation walls—all of which are time-consuming and costly to repair.
For each home, the required grade is established by the civil engineer or surveyor who’s siting the home on the lot. During construction, the excavator works from the plans to understand the grade requirements and create the grade. Throughout this work, the builder is responsible for ensuring that the grade is sited and executed correctly.
Achieving the correct grade height and slope begins by backfilling the foundation and establishing the rough grade. Later in the construction process, the final grade is established. Lastly, the landscaping is added. Completing each of these steps correctly is critical to creating a foundation grade that enables bulk water to drain away from the home.
- Prepare the area. Remove any debris from the excavation area. For a full basement, brace the walls to prevent cracking during backfilling. If any window wells are present, temporarily hold the window well drain leader while backfilling to prevent it from moving.
Use good material. Backfill using material that allows for good drainage. Make sure the backfill contains no organic materials, such as tree roots and vegetation; these materials decompose unevenly, causing the home to settle unevenly and putting additional stress on the footings. Also, make sure the backfill is free of large rocks, pieces of concrete, and other sharp objects that could puncture the insulation or waterproofing system.
Layer carefully. Backfill the corners of the foundation first for the greatest support. Then, backfill the remainder of the excavation in layers to promote even settling and minimize stress on the foundation. Be sure the excavation crew doesn't puncture the waterproofing on the foundation walls.
Establish the rough grade
Start the rough grade low. Establish the rough grade immediately after backfilling to prevent water from collecting against the foundation and to drain water away from the home. The rough grade must be low enough against the foundation to allow an 8” reveal between the bottom of the exterior finish and the final grade.
Slope the grade. Slope the rough grade away from the home to meet local code, typically so it falls a minimum of 6” within the first 10’ from the foundation. The grade has to be sufficiently sloped to drain water from the lot in accordance with the overall drainage plan for the site.
Create swales. Slope the swales per the plan, typically at least 2%. Swales direct large amounts of water away from the home and into the storm drain system. They're particularly important in areas with high rainfall.
Establish the final grade
Prepare the area. Before beginning the final grade, remove all debris from the perimeter of the home.
Maintain the reveal. Make sure the top of the foundation is a minimum of 8” above grade. This prevents the exterior finish from absorbing groundwater, and it is key to the overall strategy of protecting the home from bulk water intrusion.
Create the slope. Follow the slope already established by the rough grade. Slope the soil in front of the home toward the street. Slope the soil on the sides of and behind the home to the swales. Ensure that the front walks aren't placed too high and that they allow water to drain over, under, or through them.
Establishing the proper grade plays a major role in preventing water damage at the foundation. For more information about grading, visit the Partnership for Advancing Technology in Housing (PATH) site.
More Best Practices® for site grading and preventing water damage in homes can be found in BuildIQ® University’s online training courses House Placement & Excavation, Water Management: Basements & Crawlspaces, and Water Management: Slab-on-Grade Foundations.