Practical Engineering: When a Block Foundation Cracks

For modestly priced homes in Georgia, where I work, basement walls are usually built with 8-inch concrete masonry units (CMUs) — otherwise known as concrete blocks. It’s a relatively inexpensive way to build a sound wall that can be easily waterproofed. Unfortunately, these walls are too often built without any reinforcing steel, and that’s when the trouble begins. What the Code Says The 1992 CABO (Council of American Building Officials) One & Two Family Dwelling Code, in Table R-304.3a, does allow the use of unreinforced block walls. For 8-inch CMU walls where the cores are not filled, the maximum acceptable depth of unbalanced fill is only 4 feet. (“Unbalanced” means there is no earth on the inside of the wall,