AS 2870-2011
Site classification for residential footing design
A classification of how much your ground will move with seasonal moisture change, and the footing system that suits it. This is the report your building surveyor asks for and your structural engineer designs from.
- Standard
- AS 2870-2011
- Residential slabs and footings
- Typical scope
- 2 to 3 boreholes, 1.5 to 2.0 m
- Deeper where fill or rock is expected
- You receive
- Classification and footing recommendations
- PDF report, signed by a geotechnical engineer
- Service area
- Melbourne and regional Victoria
- Metropolitan and regional
Classifying Victorian ground since 1987- Sampled, tested and interpreted in our own NATA-accredited laboratory
- $20m public liability, $10m professional indemnity
Start here
Do you need a site classification?
If you are building a new house, units, or an extension on its own footings in Victoria, yes. Your building surveyor will not issue a permit without it, and your engineer cannot design the footings without the class.
If the block has deep fill, a steep slope, or a history as a quarry, tip or creek, a classification is not enough and you need a site investigation. We tell you that at quote stage, not after drilling.
AS 2870-2011
The site classes, and what each means for your footings
Classification is driven by characteristic surface movement, how far the ground surface is expected to swell and shrink through a normal wet-dry cycle. More movement means a stiffer, deeper or more heavily reinforced footing system.
| Class | Ground | Movement (ys) | What it usually means for footings |
|---|---|---|---|
| A | Sand and rock, stable | 0 mm | Little or no ground movement. Simplest footing systems available. |
| S | Slightly reactive clay | 0 to 20 mm | Slight movement. Standard stiffened raft or strip footings. |
| MCommon in Melbourne | Moderately reactive clay or silt | 20 to 40 mm | Moderate movement. Stiffened raft with increased beam depth. |
| H1Common in Melbourne | Highly reactive clay | 40 to 60 mm | High movement. Deeper beams, heavier reinforcement, or piering. |
| H2Common in Melbourne | Highly reactive clay | 60 to 75 mm | Very high movement. Commonly piered or stiffened raft designed to suit. |
| E | Extremely reactive clay | over 75 mm | Extreme movement. Piered systems founded below the active zone. |
| P | Problem site | Site specific | Soft or unstable soils, uncontrolled fill, landslip, abnormal moisture or mine subsidence. Requires engineered design specific to the site. |
Classes may carry a -D suffix, for example M-D or H1-D, where deep-seated moisture conditions apply: typically arid and semi-arid climatic regions.
In Melbourne, the Newer Volcanics basalt plains typically classify H1 or H2. The Silurian siltstones through the eastern suburbs are more often M.
Before you ask us
Three things people get wrong
Next door's class is not yours.
Soil changes across a street and across a block. A classification covers the footprint we drilled, not the suburb.
H2 does not mean you cannot build.
It means the ground moves a lot with the seasons, so the footings are deeper or piered. It changes the cost of the slab, not whether the house goes up.
P is not a fail.
It means the site needs its own engineered design, for fill, a slope or soft ground, rather than a standard footing from the table. Most P sites get built on.
Start to finish
What happens
- On site
- A crew drills two or three boreholes to about two metres, logs them, and takes the samples to our laboratory in Boronia. Around two hours. You do not need to be there; we need access and any known service locations. Tight-access rigs for rear yards and side setbacks.
- In the lab
- Shrink-swell and moisture testing in our own NATA-accredited laboratory. Nothing queues behind another firm's work.
- The report
- A PDF signed by a geotechnical engineer: the class on one line, footing recommendations your engineer designs from, and the borehole logs appended. We answer your engineer's or surveyor's questions at no extra cost.
No timings here. Scope, access and laboratory load all move them, and a published figure that gets missed costs more than the convenience is worth. Your quote carries a date we can hold to.
To quote, we need
The address, the build, the date, and the access
The site address or lot and plan, what you are building, when you need the report, and anything a truck cannot get past.
Common questions
Frequently asked
- How much does it cost?
- Depends on boreholes, depth and access. Send the address and what you are building and we come back with a fixed fee.
- Will drilling damage the lawn or driveway?
- Boreholes are small and backfilled. On finished surfaces we agree hole locations with you first.
- How long is a classification valid?
- No fixed expiry, but fill, excavation, tree removal or a new footprint can mean it no longer covers the work. Your surveyor will say.
- Can you do several lots in one visit?
- Yes, and it is much cheaper per lot. Send the plan of subdivision.
Related
If your site needs more than a classification
AS 1726-2017
Geotechnical site investigation
For fill, slopes, commercial structures or anything a classification cannot answer.
Learn more →AS/NZS 1547:2012
Land capability assessment
Required on unsewered land before a planning permit will issue.
Learn more →ISO/IEC 17025 · NATA 20648
Soil and rock testing
Our own laboratory. Shrink-swell, moisture, particle size, compaction.
Learn more →
Building on a residential block?
Send the site address and what you are building, and we will come back with a fixed fee and a scope. Reach us by phone or email, anywhere in Victoria.