Reinforced concrete foundation walls provide the support for the structure above, but they also must resist the lateral load from the adjacent soil, hydrostatic forces and surcharge. It is expensive and unnecessary to design the foundation wall to resist the lateral loading solely, without using adjacent structure. Concrete retaining walls are designed to resist lateral loading, but typically use large footings or tie-backs to resist overturning and sliding.
Some engineers prefer to brace the top of the wall and resist overturning with additional foundation structure, such as counterforts. The benefits of this design are the ability to backfill the wall once the concrete has curred and the top of the wall doesn’t need to extend to the floor structure above. The down side to counterforts is they are an additional structure and expense. To work properly, they must be installed fairly often to provide enough dead load to resist overturning.
When possible, we prefer to brace the top of the wall with the adjacent floor structure. This design takes advantage of the existing floor framing. It is cost-effective and typically only requires additional nailing between the bottom of the joist and the sill plate and blocking where the joists are parallel to the foundation walls. Our clients use temporary bracing if the walls need to be backfilled prior to the installation of the floor framing above.
We understand that architectural design and site conditions greatly effect the design of the foundation, but whenever possible we try to be economical with our foundation structure. To learn more about concrete design visit the Reinforced Concrete Construction section of our blog.