Adelaide block check
Soil Classification (M, H1, H2, P): What It Means for Your Footings
Quick answer
A soil classification for a new Adelaide home is issued under Australian Standard AS 2870. Classes range from A (stable) through S, M, H1, H2, E to P (problem site). Most Adelaide blocks return M or H1. The class drives footing type, slab depth and reinforcement, and it is set by a soil test before footings are engineered.
Adelaide sits on some of the most reactive clay soils in Australia. A soil test on your block returns a classification under AS 2870, and that letter drives everything downstream: footing type, slab depth, engineering, and cost. Understanding the class up front removes surprises later.
Public source: Australian Standard AS 2870 Residential slabs and footingsSection 1
Class A: stable
Sand and rock sites with little to no movement. Rare in metropolitan Adelaide. Standard footings, no special engineering.
Section 2
Class S: slightly reactive
Slight surface movement possible. Uncommon in Adelaide but appears in some coastal sand-belt suburbs. Standard footings with minor allowances.
Section 3
Class M: moderately reactive
Moderate clay movement. Very common across Adelaide plains. Waffle slabs or stiffened raft slabs are typical. Most volume builders design their standard slab for M class as a baseline.
Section 4
Class H1: highly reactive
Significant clay movement. Common across the western suburbs, the plains, and some Hills areas. Deeper footings, thicker slabs, more reinforcement, and sometimes edge beams driven further down. Meaningful engineering upgrade over M class.
Section 5
Class H2: very highly reactive
Very high clay movement. Common on the deeper black clay plains north and west of Adelaide. Piered slabs, screw piles, or bored concrete piers into more stable strata are often required. This is where footings costs climb sharply.
Section 6
Class E: extremely reactive
Extreme movement. Rare but possible on specific parcels. Engineered pile systems, sometimes coupled with suspended slabs. Requires bespoke geotechnical and structural engineering.
Section 7
Class P: problem sites
Fill, softness, uncontrolled soil movement, mine subsidence, or a combination. Requires site-specific engineering: piers to rock, ground improvement, or removal and replacement of fill. Cannot be designed off a standard footing table.
| Class | Reactivity | Adelaide prevalence | Typical footing response |
|---|---|---|---|
| A | Stable | Rare (sand/rock) | Standard footings |
| S | Slightly reactive | Coastal sand belt | Standard footings, minor allowances |
| M | Moderately reactive | Very common (plains) | Waffle or stiffened raft slab |
| H1 | Highly reactive | Common (western/plains) | Deeper footings, thicker slab, more reinforcement |
| H2 | Very highly reactive | Deep black clay (N/W) | Piered slabs, screw piles, bored piers |
| E | Extremely reactive | Rare specific parcels | Engineered pile systems, suspended slab |
| P | Problem site | Fill / mine / mixed | Bespoke geotechnical + structural engineering |
Section 8
How to find out early
Any builder or designer can commission a soil test on the block before you commit to a design. It is inexpensive relative to redoing engineering later. If you are buying land, ask the vendor whether a test has already been done. If yes, ask for it. If no, factor a test into your due diligence.
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Learn moreThis is general planning and technical information drawn from public sources. It is not legal, planning, or engineering advice. Rules and overlays change; always confirm current requirements directly through SAPPA and engage a qualified professional (town planner, building designer, private certifier, arborist, or geotechnical engineer) for your specific block.