What is the maximum unbalanced backfill height for basement walls in residential buildings?
The maximum unbalanced backfill height depends on the foundation wall construction, foundation wall thickness, and soil type. The 2003 International Residential Code (IRC) Table R404.1.1 (1) provides requirements for foundation walls constructed with plain (i.e., not reinforced) concrete or masonry, and Tables R404.1.1(2)-R404.1.1(4) provide requirements for reinforced concrete and masonry walls. As an example, a nine-foot foundation wall constructed with eight-inch thick solid or fully grouted masonry, and no reinforcement can support four feet of unbalanced backfill. Foundation walls should have lateral support at the top and bottom unless the height of unsupported backfill is 48 inches or less. Lateral support can be provided by the basement slab on the bottom and by the floor diaphragm on the top of the wall.