What is the recommended thickness for a foundation under masonry chimneys?

The recommended thickness for a foundation under masonry chimneys is typically 1 foot (12 inches). This thickness provides the necessary strength and stability to support the weight of the chimney and to accommodate any settling that may occur over time. A thicker foundation helps to prevent cracking and movement, which can lead to serious structural issues. It’s important for the foundation to be adequately sized, as a masonry chimney can be quite heavy and requires a solid base to ensure safety and longevity. While other options suggest thinner foundations, they do not provide the level of support recommended for such structures, potentially increasing the risk of failure.