What is site classification in a soil report?

Site classification is the system used in the team soil reports to categorise ground conditions and determine how deep footings must be placed and how slabs should be constructed. Under the standard AS2870 (the team Standard for Residential Slabs and Footings), soil is rated into one of seven classes: A, S, M, H, E, P, or U (unsatisfactory). Each class reflects different levels of soil movement risk and load-bearing capacity.

The six main classes work like this: Class A soils are stable and require only shallow footings (typically 450 mm). Class S soils are slightly reactive and need slightly deeper footings (600 mm). Class M soils show moderate reactivity and require deeper footings (750 mm). Class H soils are highly reactive, usually clay, demanding footings at 900 mm or more. Class E soils are extremely reactive and require special design. Class P soils are problem soils (fill, contamination, or unstable ground) that need site-specific engineering. Class U means the site is unsatisfactory for standard construction.

Builders and homeowners need this classification because it directly affects construction cost and method. A Class A site might use a simple shallow slab-on-ground. A Class H or E site could require deeper footings, reinforced slabs, moisture barriers, and sometimes specialised waterproofing or underpinning. A soil report with proper site classification is usually required before building work starts, particularly on sloping or challenging blocks. Without it, builders cannot legally design compliant foundations, and homes risk cracking or structural movement.