How wide should the footer be for a CMU wall?

• A. Twice the width of the block
• B. Three times the width of the block
• C. Equal to the depth of the frostline
• D. Equal to the width of the block

Answer: (A)

Distributing the load over a wider base is the main idea. A CMU wall needs a footing wider than the wall itself so the soil carries the weight and resists settlement and frost movement. The common rule of thumb is about twice the width of the block. For standard 8-inch CMU blocks, that means roughly a 16-inch-wide footing, which provides adequate bearing area without being excessive. Using a footing as wide as the block would leave too little bearing area and increase settlement risk. The frost depth concept relates to how deep the footing must go, not how wide it should be, so it doesn’t apply to width. A footing width three times the block is generally more than necessary for typical residential walls and adds unnecessary cost.