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 is set by a soil test, and it is what your engineer uses to design the foundation. A more reactive class generally means a stronger foundation and a higher cost.
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 is what your engineer uses to design the foundation, which in turn flows through to your build 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. A standard engineered slab is usually designed for this, and most volume builders use M class as their baseline.
Section 4
Class H1: highly reactive
Significant clay movement. Common across the western suburbs, the plains, and some Hills areas. This usually means a stronger, more engineered foundation than M class, which your engineer designs for the block.
Section 5
Class H2: very highly reactive
Very high clay movement. Common on the deeper black clay plains north and west of Adelaide. This typically calls for a more heavily engineered foundation again, and it is where foundation costs start to climb sharply.
Section 6
Class E: extremely reactive
Extreme movement. Rare but possible on specific parcels. These blocks need a bespoke foundation designed by a structural and geotechnical engineer.
Section 7
Class P: problem sites
Fill, softness, uncontrolled soil movement, mine subsidence, or a combination. These sites need site-specific engineering designed by a qualified engineer, and cannot be worked out from a standard footing table.
| Class | Reactivity | Adelaide prevalence | What it usually means |
|---|---|---|---|
| A | Stable | Rare (sand/rock) | A standard foundation |
| S | Slightly reactive | Coastal sand belt | A standard foundation, minor allowances |
| M | Moderately reactive | Very common (plains) | A standard engineered slab |
| H1 | Highly reactive | Common (western/plains) | A stronger, more engineered foundation |
| H2 | Very highly reactive | Deep black clay (N/W) | A more heavily engineered foundation; cost climbs |
| E | Extremely reactive | Rare specific parcels | A bespoke foundation your engineer designs |
| P | Problem site | Fill / mine / mixed | Site-specific engineering by a qualified engineer |
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.
What the pros read before they build on your block
How to read a soil report
The pro reads the classification line first, then the reactive movement number the report gives it, then whether the holes were drilled on your block or borrowed from next door. A class M on a real bore log is a number you can build to. A class M assumed off a neighbouring site is a guess wearing a suit.
Read the guideHow to read an engineering drawing
A supervisor reads the footing plan alongside the soil report, because the two have to agree. The report says how reactive the ground is, and the slab drawing has to be the system that class demands. If the report says H2 and the drawing is a thin class M raft, someone has priced the wrong slab, and you find out with a crack, not a phone call.
Read the guideHow to read a site plan and contour survey
A supervisor reads the site plan from the levels down. The little numbers scattered across the block are spot heights, and the difference between the highest and lowest one is the whole story. Under 300mm across the house footprint is an easy block. Over a metre and someone is building retaining walls.
Read the guideKeep reading
Find a town planner
Overlay-heavy block? A planner reads the code and pre-lodges advice.
Learn moreFind a private certifier
Ready for Planning + Building Rules Consent? A certifier can move fast.
Learn moreFind a building designer
Need drawings that respect the overlay? Start with a designer.
Learn moreCouncil approvals in Adelaide
The full pillar covering PlanSA, DCS levies, and the council pathway.
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.