August 17, 2026

Footing Design Melbourne | Structural Engineer Foundation Design

Q: What is an AS 2870 site classification and why does it matter?

AS 2870 classifies building sites from Class A (stable, non-reactive soils) to Class E (extremely reactive soils) based on a geotechnical assessment. The classification directly determines what type of footing is required, how deep it must be and how heavily it must be reinforced. A building on footings designed for the wrong site class is at increased risk of movement and structural damage.

Footing Design in Melbourne: What a Structural Engineer Does

Footing design is one of the most technically demanding aspects of any construction project. Get it right and the building stands safely for decades. Get it wrong and the consequences range from cracking and movement to costly structural failure. For Melbourne properties, which sit on some of Australia's most reactive clay soils, footing design requires careful engineering analysis, not guesswork. Principal Built Engineering provides structural engineering services that include footing design for residential, commercial and industrial projects across Melbourne and Victoria.

Key Point: Footing design in Melbourne must account for the reactive clay soils common across the metropolitan area. These soils shrink and swell with seasonal moisture changes, which can cause significant movement in buildings founded on poorly designed footings.

What Is Footing Design?

Footing design is the engineering process of specifying the type, dimensions, depth and reinforcement of the concrete elements that transfer a building's loads into the ground. A structural engineer designing footings must understand both the loads coming from the structure above and the bearing capacity and behaviour of the soil below.

The footing must perform two functions reliably. First, it must spread the structural loads so the soil is not overstressed. Second, it must provide enough stiffness to prevent differential settlement, which is uneven movement between different parts of the building that causes cracking in walls, floors and ceilings.

In Victoria, residential footing design must comply with AS 2870 (Residential Slabs and Footings) and AS 3600 (Concrete Structures). For commercial and industrial buildings, the structural engineer designs footings to the relevant Australian Standards based on the calculated loads and site conditions.

Types of Footings Used in Melbourne

Not every footing type suits every site or project. A structural engineer selects the appropriate footing system based on the site classification, the loads to be transferred and the specific ground conditions found during the geotechnical investigation.

Footing Type	Typical Application	Melbourne Site Suitability
Strip Footings	Under load-bearing walls in houses, extensions and low-rise buildings	Common on Class A and Class S sites. Depth increases on reactive clay sites.
Pad Footings	Under individual columns in commercial, industrial and framed structures	Suitable across site classes. Size and depth determined by column load and soil bearing capacity.
Raft Slabs	Residential slabs on reactive clay, where uniform support across the full footprint is needed	Very common in Melbourne's eastern and south-eastern suburbs due to high-reactive clay.
Waffle Slabs	Residential construction on Class M to Class H sites	Widely used across Melbourne where Class M or H classification applies.
Bored Pier Footings	Where near-surface soils are weak or highly reactive and deeper stable material is required	Common in areas with filled ground, soft or highly reactive near-surface soils.
Screw Piles	Decks, pergolas, retaining walls, light structures where vibration-free installation is needed	Used across Melbourne for structures where concrete footings would disturb services or adjacent structures.

Melbourne Soil Conditions and Their Effect on Footing Design

Melbourne's geology creates some of the most challenging conditions for footing design in Australia. Much of the metropolitan area, particularly the eastern, south-eastern and northern suburbs, is underlain by reactive clay soils. These soils change volume significantly as moisture content changes seasonally. The result is ground movement that can lift or settle footings unless the design accounts for this behaviour.

Note: AS 2870 classifies residential sites from Class A (stable, non-reactive) through to Class E (extremely reactive). The site classification directly controls the footing design requirements. An engineer reviewing a building with cracking often finds the footing was designed for a lower class than the soil actually warrants.

Site classification under AS 2870 is based on a geotechnical investigation that measures the soil's shrink-swell index. In Melbourne:

Class A sites are uncommon, mainly sand-based areas near the bay and coast
Class S sites occur in less reactive areas, some parts of the western suburbs
Class M sites are very common across inner and middle Melbourne suburbs
Class H1 and H2 sites are typical in outer eastern suburbs including Narre Warren, Berwick, Pakenham
Class E sites occur where soils have very high shrink-swell potential, often in dry, exposed locations

Beyond reactivity, Melbourne sites can present other footing design challenges including: filled or made ground in former industrial areas, soft alluvial soils near waterways such as the Yarra and Maribyrnong, and sites with variable bedrock depth. Each of these conditions requires a specific engineering response in the footing design.

The Footing Design Process

A thorough footing design follows a structured process. Shortcuts in any phase increase the risk of footing failure or costly remediation.

Site Investigation

Geotechnical report commissioned to identify soil types, bearing capacity, groundwater level and site classification under AS 2870.

Load Analysis

Structural engineer calculates loads from the building above: dead loads (structure self-weight), live loads (occupancy and contents), wind and other applicable loads.

Footing Selection

Engineer selects the most appropriate footing type based on site classification, loads, building type and any constraints such as proximity to existing structures or services.

Design and Calculations

Footing dimensions, depth and reinforcement specified. Calculations prepared to AS 2870 (residential) or AS 3600 (commercial and industrial) demonstrating compliance.

Documentation

Footing layout drawings, details and specifications prepared for inclusion in the building permit set. Structural engineer signs the documents.

Construction Review

Structural engineer may inspect footings during excavation to verify ground conditions match the design assumptions before concrete is poured.

The geotechnical report is a critical input. A footing designed without a geotechnical investigation is working from assumptions about the ground that may not reflect reality. For commercial and industrial projects, a geotechnical investigation is standard practice. For residential extensions and additions, the engineer may review existing documentation or recommend a targeted investigation where site conditions are uncertain.

When Do You Need a Structural Engineer for Footing Design?

In Victoria, a registered structural engineer must design footings for commercial, industrial and multi-residential projects. For residential buildings, the requirement depends on the site classification and the nature of the work. Under AS 2870, standard residential footings on Class A to Class M sites can be designed using the deemed-to-comply tables in the standard, but higher site classes or non-standard situations require an engineer.

When to engage a structural engineer for residential footing design: Site classification H1, H2 or E; sloping sites; sites with filled ground or known problem soils; extensions to existing buildings where the existing footing depth is uncertain; any project where the building certifier requires engineering certification.

Beyond new construction, a structural engineer providing structural engineer inspections can assess whether existing footings are performing as intended and whether any observed cracking or movement relates to footing distress. Early inspection often identifies problems while remediation options are still straightforward.

For retaining walls, footing design is part of the overall wall design. Retaining walls over one metre in height generally require engineering design. Principal Built Engineering provides retaining wall engineering that includes footing design as part of the complete structural package.

AS 2870

Residential footing standard in Victoria

Site classification levels (A, S, M, H1, H2, E)

CPEng

PBE engineer registration level

Principal Built Engineering carries CPEng, RPEQ and RPEV registration. Their engineers design footings across a range of project types, from residential extensions to large commercial and industrial facilities. Read more about their structural engineer reports and how documentation is prepared for footing and foundation projects.

Frequently Asked Questions

What is footing design and why is it important?

Footing design is the engineering process of specifying the concrete elements that transfer a building's structural loads into the ground. It is important because an undersized, too-shallow or poorly reinforced footing will move or fail under load, causing cracking, structural damage and potentially requiring expensive underpinning or reconstruction. In Melbourne, reactive clay soils make footing design particularly important because seasonal soil movement can lift or settle footings that are not engineered for those conditions.

What type of footing is used for a house in Melbourne?

The most common footing types for houses in Melbourne are waffle slabs and raft slabs, both of which are slab-on-ground systems designed to accommodate soil movement. Strip footings under load-bearing walls are used in some areas, and bored piers are used where near-surface soils are weak or highly reactive. The correct footing type depends on the site classification under AS 2870, which is based on the soil's reactivity as measured by a geotechnical investigation.

How deep do footings need to be in Melbourne?

Footing depth in Melbourne varies with site classification. On Class M sites, residential strip footings typically extend to 300 to 450 mm. On higher classification sites (H1, H2), deeper footings or bored piers may be required to reach soil that is less affected by seasonal moisture variation. The structural engineer specifies footing depth as part of the design based on the geotechnical report findings and the calculated loads. There is no single standard depth that applies across all Melbourne sites.

Do I need a structural engineer for footing design in Victoria?

For commercial, industrial and multi-residential projects in Victoria, a registered structural engineer must design and certify the footings. For residential construction, the requirement depends on the site classification and the scope of work. Class H1, H2 and E sites, sloping sites, filled ground and extensions to existing buildings with uncertain footing conditions all typically require a structural engineer. The building certifier for the project will advise whether engineering certification is required for the specific work.

What is an AS 2870 site classification and why does it matter?

AS 2870 is the Australian Standard that governs the design of residential slabs and footings. It classifies building sites from Class A (stable, non-reactive soils) to Class E (extremely reactive soils). The classification is based on a geotechnical assessment of the soil's shrink-swell index. The classification directly determines what type of footing is required, how deep it must be and how heavily it must be reinforced. A building constructed on footings designed for the wrong site class is at increased risk of movement, cracking and structural damage over time.

Need footing design for a project in Melbourne? Contact Principal Built Engineering to discuss your site conditions and structural requirements. The team provides footing design for residential extensions, commercial fitouts and industrial facilities across Melbourne and Victoria.

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