Footing Requirements for Construction on or Near Slopes in Southern California

Footings on or adjacent to descending slope surfaces must be embedded and set back sufficiently from the slope to provide stable vertical and lateral support. The top surface of all footings must be level, and the bottom surface cannot exceed a 10-percent slope. When the natural ground slope requires it, footings must be stepped.

When building on or next to a slope in Southern California, footings must be carefully designed and constructed to ensure long-term stability and structural integrity. All footings located on or adjacent to sloping surfaces need to be founded in soil that provides enough embedment and setback from the slope. This is crucial for both vertical and lateral support, preventing detrimental settlement over time.

Key Requirements for Footings on Slopes

There are specific rules that govern how footings should be formed when encountering a slope:

• Level Top Surface: The top surface of any footing must always be level. This ensures that the foundation walls or framing built on top have a flat, stable base.
• Maximum Bottom Slope: The bottom surface of a footing cannot have a slope exceeding 1 unit vertical in 10 units horizontal (a 10-percent slope). If the natural grade slope is steeper than this, the footing must be stepped. This ensures the footing has adequate bearing capacity and doesn't slide.
• Stepped Footings: Footings must be stepped where the elevation of the top surface needs to change, or when the bottom surface's slope would otherwise exceed the 10-percent limit. Stepping allows the footing to follow the general contour of the land while maintaining level sections and proper bearing.

In our experience, properly stepping footings is a common practice on hillside properties throughout Southern California, from the coastal hills of Orange County to the sloped lots in Riverside.

> Pro Tip: For properties with significant slopes, especially those steeper than 33.3-percent (1 unit vertical in 3 units horizontal), a qualified geotechnical engineer will likely be required to provide specific recommendations and ensure compliance with more stringent code sections.

Special Considerations for Steeper Slopes

For buildings and structures situated on or adjacent to very steep slopes—specifically, those steeper than 1 unit vertical in 3 units horizontal (33.3-percent slope)—additional, more detailed regulations apply. In these situations, the local building department will require compliance with specific sections of the residential code that detail placement and foundation design. This often involves more extensive engineering and geological review due to increased risks of instability.

In some cases, especially in seismic zones D0, D1, and D2 (common throughout Southern California), exterior walls and certain interior braced wall panels require continuous solid or fully grouted masonry or concrete footings to provide robust support. This reinforcement helps the structure withstand seismic activity and ensures stability on challenging terrains. We generally recommend consulting our guide on Continuous Footing Requirements in SoCal Seismic Zones D0, D1, D2 for more detailed information.

Common Mistakes

• Ignoring Geotechnical Reports: Failing to obtain or properly interpret a geotechnical report for sloped sites can lead to inadequate footing design and future settlement issues.
• Improper Stepping: Not stepping footings correctly or exceeding the maximum allowable bottom slope can compromise the foundation's stability.
• Insufficient Embedment/Setback: Placing footings too close to the edge of a slope without proper embedment leaves them vulnerable to erosion and lateral movement.
• Poor Compaction: Not properly compacting the subgrade beneath stepped footings can lead to differential settlement and cracking.

When planning a foundation project on a sloped site in Southern California, it's essential to understand these requirements. For a custom foundation plan tailored to your specific property's conditions, reach out to Western Concrete to discuss your project.