Raft Slabs Sydney | Stiffened Raft Slab Construction

What Is a Raft Slab?

A Slab and Footing System That Acts as One

A stiffened raft slab is a ground-level concrete slab with integral stiffening beams — also called ribs — cast monolithically so the whole slab acts as one rigid mass. Rather than transferring loads through separate point footings, the beam-and-slab system distributes load evenly across the footprint beneath it.

This is what makes the stiffened raft the standard footing solution for reactive and clay-rich soils across Greater and Western Sydney. As the soil moves or swells, the slab moves with it as a single unit rather than in sections. Every raft slab we build is constructed to the structural engineer's design and to Australian Standard AS2870.

Integral stiffening beams cast monolithically with the slab
Built to AS2870 and the structural engineer's design
Standard solution for reactive clay and Class M, H and E sites
Excavation, formwork, steel and pour — managed by one team
Fixed-price quote within 24 hours — no deposit, no obligation

Why Raft

What Makes a Stiffened Raft the Right Choice

Six reasons builders and owner-builders across Sydney specify a stiffened raft for reactive and clay-heavy sites.

Designed for Reactive Clay

The monolithic beam-and-slab system distributes movement across the whole footprint, making it the proven solution for Class M, H and E sites common throughout Greater Sydney.

Rigid Monolithic Pour

Slab and beams are cast in a single pour, bonding them into one structural unit. There are no construction joints between the footing and the slab — it all moves together.

Engineered Stiffening Beams

Beam depth, width, spacing and reinforcement are specified by the structural engineer for each site. We build to those drawings — not a generic template.

Suits Most Home Builds

Stiffened rafts are suitable for single-storey and double-storey homes, granny flats, duplexes and most residential builds across the Greater Sydney basin.

Excavation & Footings Included

The scope covers trench excavation, sub-base preparation, formwork and all steel work. There is no split between a separate excavator and a separate concretor — one team handles the complete job.

One Accountable Team

One team manages the whole job from initial cut to the finished slab — one point of contact, one party accountable for the schedule, the quality and the result.

Our Process

How Your Raft Slab Gets Built

Three stages, managed by one team from the engineering drawings to the finished and cured slab.

Engineering & Excavation

We work from the structural engineer's drawings. The beam trenches are excavated to the specified depth and width, the sub-base is prepared, and any required inspections are arranged before steel goes in.

Formwork, Beams & Steel

Perimeter and internal formwork is set to level, the beam steel and slab reinforcement mesh are placed to the engineer's specification, and all penetrations are formed before the pour is booked.

Monolithic Pour & Cure

The slab and all beams are poured in one continuous operation — no cold joints, no separate pours. The concrete is finished to the specified level and allowed to cure before handover.

Slab Types

Compare Raft vs Waffle Pod

Both are stiffened raft systems. The engineer specifies which one suits your site.

Raft Slab

Beams formed in excavated trenches, slab sits at ground level. The standard approach for sites with significant reactive soil depth or where the engineer specifies trenched construction.

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Waffle Pod Slab

Beams formed above existing ground using void-former pods. Requires less excavation and suits sites where a raised floor level or minimal ground disturbance is specified.

Learn about waffle pod slabs

Also building a house slab? See our full house slab services page.

Pricing

What Affects the Cost of a Raft Slab?

Every Job Is Quoted on the Engineering Plans

Slab area and overall footprint
Beam layout, depth and spacing from engineering
Soil class and excavation depth required
Site access and ground conditions

We price each raft slab from the structural engineer's drawings and the site conditions — so the number you receive reflects the actual job. Send us your plans and we'll have a fixed-price quote back to you within 24 hours. No deposit to quote and no obligation.

FAQ

Raft Slab Questions Answered

A raft slab is a ground-level concrete slab with integral stiffening beams (ribs) cast monolithically so the whole slab acts as one rigid mass. Rather than transferring loads through separate footings at points, the entire slab and beam system works together to distribute loads evenly across the ground beneath it. This makes it well suited to sites where the soil can move or settle.

Both are stiffened raft systems that form a rigid mass, but they differ in how the beams are formed. A conventional raft slab is formed using excavated trenches — the beams are cast into the ground. A waffle pod slab sits on top of the existing ground level, with the beams formed using void formers (pods) placed between them. The structural engineer specifies which system suits the soil class, site conditions and building design.

A stiffened raft slab is the term used in Australian standard AS2870 for a ground-level slab that incorporates a grid of integral reinforced concrete beams (stiffening ribs) cast as one monolithic unit. The stiffening beams give the slab the rigidity to resist differential movement in reactive or clay soils, so the structure above moves together rather than in sections.

Yes. Every raft slab we build is constructed to the structural engineer's design — including beam depths, widths, spacings, steel specifications and concrete strength. We work from the engineering drawings provided and do not deviate from the design without written direction from the engineer.

Yes. Stiffened raft slabs are specifically designed for reactive and clay-rich soils common across Greater and Western Sydney. The monolithic beam-and-slab system distributes movement across the whole footprint rather than allowing sections to move independently, which is what makes it the standard footing system for Class M, H and E sites under AS2870.

Yes. The scope covers the full job — excavation of the stiffening beam trenches, sub-base preparation, formwork, steel placement, any inspections required, and the monolithic pour. One team manages the whole job from the initial cut to the finished and cured slab, so there is one point of contact and one party accountable for the result.

Raft Slabs, Built to Engineer's Spec