A stem wall slab foundation is a foundation system constructed in multiple stages, featuring a concrete footer poured at the original ground level, a vertical wall (the "stem wall") built upon the footer, and finally, a concrete slab poured on top of the area enclosed by the stem wall.
Understanding Stem Wall Slab Foundations
This type of foundation combines elements of a deep foundation (the footer and stem wall extending below the final slab level) and a shallow foundation (the slab itself). It is commonly used when the finished floor elevation needs to be raised above the existing grade, often due to sloping terrain, flood risks, or the need for a crawl space or elevated slab.
The Construction Process
As described in the reference, stem-wall slabs are constructed in a multi-part process where a footer is poured at virgin ground level, then blocks are laid forming a wall up to the finished slab elevation. This multi-stage approach ensures structural integrity by bearing the load on undisturbed soil.
The process typically involves:
- Excavation: Trenches are dug for the footer around the perimeter.
- Footer Pour: Concrete footers are poured into these trenches at the virgin ground level. These footers distribute the building's load over a wider area.
- Stem Wall Construction: Blocks (such as concrete masonry units - CMUs) or poured concrete are used to build the vertical stem wall on top of the footer. The height of this wall determines the final elevation of the slab.
- Backfilling and Grading: Fill dirt may be placed and compacted within the area enclosed by the stem wall to prepare for the slab.
- Slab Pour: A concrete slab is poured on top of the compacted fill and the interior edges of the stem wall, creating the floor surface for the structure.
Key Advantages
One significant benefit of using a stem wall slab foundation is its stability, particularly in certain ground conditions. The reference notes that This type of foundation is much more stable when fill dirt is required achieve the final build elevation. This is because the stem wall rises from a stable footer on undisturbed soil, providing better support for the elevated slab, even when significant backfill is used.
Main Components
The primary components of a stem wall slab foundation include:
- Footer: The base layer of concrete poured directly on the excavated ground.
- Stem Wall: The vertical wall constructed on the footer, typically made of CMU blocks or concrete.
- Slab: The concrete floor surface poured on top of the stem wall and compacted fill.
