AS 2870 Explained: Soil Classes & Their Impact on Residential Concrete Slabs
AS 2870 - Residential slabs and footings - remains the governing standard for most house builds and extensions in Australia.
Soil Class Quick Reference
- A - Stable, sandy soils - minimal movement
- S - Slightly reactive
- M - Moderately reactive (most common across suburbs)
- H1 / H2 - Highly reactive - significant seasonal movement
- P - Problem sites - soft soils, fill, trees, mining subsidence, etc.
Design Implications
- Class A/S → standard 100 mm slab, light reinforcement
- Class M → stiffened edge beams, more mesh
- Class H1/H2 → deeper edge beams, waffle pods or piers
- Class P → site-specific engineer design required
Most Common Mistakes
- Skipping a soil test (site classification report)
- Ignoring tree roots or poor drainage near slab
- Using standard designs on highly reactive sites
A proper site classification can prevent major cracking and costly rectification claims years later.
We coordinate soil testing and professional slab designs for peace of mind.
Published: October 20, 2025 | 8 min read