What is the maximum fill height under a slab when using dirt or sand?

The maximum fill height under a slab when using dirt or sand is 8 inches. This guideline is crucial in ensuring the structural integrity of the slab and the safety of the building. When fill material is placed beneath a concrete slab, it must be adequately compacted to prevent future settlement or movement, which can lead to cracking or failure of the slab.

If the fill height exceeds the recommended maximum, it can create issues with compaction and increase the risk of uneven settlement. Additionally, as the fill height increases, the potential for issues related to moisture retention and drainage also rises, which can further compromise the slab and the overall building structure. The choice of 8 inches for maximum fill height balances the needs for proper support and long-term stability of the concrete slab.