What is the maximum fill height under a slab when using gravel?

When considering the use of gravel as a fill under a concrete slab, the maximum fill height is typically determined by building codes and engineering standards that ensure stability, drainage, and proper structural support.

A fill height of 24 inches is acceptable because it allows for adequate compaction and drainage when gravel is used. Gravel is preferred in these applications because it promotes drainage, preventing water from pooling beneath the slab, which can lead to heaving or settling issues. When the fill material is properly compacted and tested, a fill height of up to 24 inches under the slab is considered manageable and safe for most residential construction applications.

In contrast, options like 12 inches, 18 inches, or 36 inches may not align with common practices for multiple reasons such as insufficient support at lower heights or increased risk of structural issues at excessively high levels. The 24-inch height strikes a balance between providing sufficient support and maintaining efficient drainage, making it the most appropriate choice in this context.