Foundation Engineering
Everything above ground depends on what happens below it
Footings are the interface between your building and the ground. They take every load the structure generates, from the weight of the roof and walls through to wind uplift and earthquake forces, and transfer those loads safely into the soil. If the footings are undersized, the building settles. If they are not deep enough, the soil moves beneath them. If they are not stiff enough, the walls crack. Getting the footing design right is not something you compromise on.
In Australia, footing design is governed by AS 2870 for residential buildings and AS 3600 for commercial and industrial structures. The starting point for every design is the geotechnical report, which tells us what the soil is doing and how it is likely to behave over the life of the building. Soil reactivity, bearing capacity, water table depth, and the presence of fill material all influence the footing system we recommend.
Our team has designed footings for hundreds of projects across Sydney and NSW, from single-storey houses on stable sand through to multi-level commercial buildings on highly reactive clay. Every design is tailored to the specific site, the specific loads, and the specific soil conditions, because no two sites are the same and no two footing designs should be either.
Strip footing excavation with reinforcement cages placed and ready for concrete placement on a residential site.
Choosing the right footing system
The footing type depends on what the building looks like, how heavy it is, what the soil is doing, and how deep you need to go to find stable ground. Here is how we think about it:
Strip Footings
Continuous concrete footings that run beneath load-bearing walls, distributing the wall load along the length of the footing and into the soil below. Strip footings are the most traditional footing type and remain widely used for masonry construction, boundary walls, and situations where the building loads are carried primarily by walls rather than columns. The width and depth of the strip depend on the wall load and the soil bearing capacity.
Pad Footings
Isolated footings that support individual columns or point loads. Each pad spreads the column load over a sufficient area of soil to keep the bearing pressure within the allowable capacity. Pad footings are the standard choice for steel and timber frame buildings where loads come down at discrete column locations. We size each pad individually based on the column load it carries, and we check for one-way shear, two-way punching shear, and bending in both directions.
Raft Footings
A large, continuous footing that covers the entire building footprint and distributes the total building load across the full area. Raft footings are the go-to solution for reactive soils where differential ground movement is the primary design concern. They provide stiffness to resist the bending and twisting forces that soil heave and shrinkage impose on the building. On Class M, H, and E sites, raft footings with stiffening beams are often the most reliable option.
Pile Footings
Deep foundation elements that bypass weak or unstable surface soils and transfer building loads to stronger strata further down. Piles can be bored (drilled in place and filled with reinforced concrete) or driven (precast concrete or steel sections hammered into the ground). We use piles when the surface soils have insufficient bearing capacity, when the site is on fill, or when the building loads are too heavy for shallow footings. Each pile is designed for axial capacity, lateral load, and settlement.
"You can fix almost anything above ground. Fixing a footing after the building is up is a completely different problem."
IA Engineering Design Team
Understanding soil classification
Under AS 2870, every residential site in Australia is assigned a soil classification based on how reactive the ground is, meaning how much it shrinks when it dries out and swells when it gets wet. This classification is determined by the geotechnical engineer from site investigation data, and it directly drives the footing system we design.
Class A and S sites
Stable to slightly reactive. These are the easiest sites to build on. Sand, rock, and low-plasticity soils with minimal moisture sensitivity. Standard strip footings or simple raft slabs are usually sufficient, and the reinforcement and beam depths are modest. Most sites in sandy coastal areas fall into this category.
Class M sites
Moderately reactive. The ground will move noticeably with seasonal moisture changes, and the footing system needs to be stiff enough to resist that movement without allowing the building to distort. Stiffened raft slabs with internal beams are the standard approach. The beam depths and reinforcement step up from Class S.
Class H1, H2, and E sites
Highly to extremely reactive. These are the challenging sites, and they are more common across Western Sydney and the Cumberland Plain than many people realise. The ground can move 40, 60, or even 80 millimetres with changes in moisture. The footing system needs deep stiffening beams, heavy reinforcement, and careful attention to moisture management around the perimeter. On Class E sites, pier-and-beam or pile systems may be required to take the building loads below the reactive zone entirely.
What goes into the engineering
A footing design is more than just picking a type and a size. The engineering considers a range of interrelated factors to make sure the foundation performs over the full design life of the building.
Bearing capacity is the fundamental check. The soil beneath the footing must be able to support the applied loads without excessive settlement or shear failure. We use the bearing capacity values from the geotechnical report and check that every footing keeps the contact pressure within the allowable limit, with appropriate safety factors applied.
Settlement analysis ensures the building does not sink more than the structure and finishes can tolerate. Total settlement and differential settlement between adjacent footings are both checked. Differential settlement is usually the more critical criterion, because it causes walls to crack, doors to jam, and floors to slope.
Reactive soil design is unique to the Australian context. On reactive sites, the footing is not just resisting gravity loads, it is resisting the forces imposed by the ground itself as it swells and shrinks. The stiffening beams in a raft footing act like the keel of a ship, keeping the building rigid while the soil moves beneath it. The deeper and stiffer the beams, the more movement the footing can tolerate without distress.
Standards & Compliance
Every footing design is certified to Australian Standards
All footing designs are prepared in accordance with the relevant Australian Standards and certified by our Registered Professional Engineers (RPE). Documentation is council-ready and suitable for building certification.
How we work with you
We start with your geotechnical report and architectural plans. The soil classification and bearing capacity data drive the footing type selection, while the architectural layout and structural loads determine sizes, depths, and reinforcement requirements.
From there, we develop the complete footing design: footing plan layout, cross-sections, reinforcement details, concrete specification, and any special provisions for steps, rebates, penetrations, or connections to existing structures. For reactive sites, we include moisture management recommendations and articulation joint locations.
The deliverable is a complete set of structural drawings and a design certificate, ready for council submission and construction. We stay available throughout the build for site queries, builder questions, and inspections at hold points. Our goal is a smooth path from design to a footing that performs exactly as intended for the life of the building.