A level slab does not mean level ground underneath it.
On a sloping site, the low side of the building can bring together fill, a slab panel, an edge beam and a change in footing level. They may appear to be one detail on the drawing. They do not all have the same support requirements.
That is the useful question for this week's Friday Detail: what supports each element, and how is the change in level resolved?
We continue NCC 2022 Part 4.2 with clause 4.2.6, slab edge support on sloping sites, and clause 4.2.7, stepped footings. Last week's ground preparation and slab support article established the foundation options. This week follows those options down the slope.
Confirm the pathway before reading the detail
This is an NCC 2022 education series for the residential work addressed by Volume Two and the ABCB Housing Provisions. It is not a footing design service.
Part 4.2 is subject to the limitations in Volume Two H1D4(2). A site class alone does not establish that every Housing Provisions detail is available. Check the complete application limits, the site information, the documented design pathway and the applicable jurisdictional provisions.
If you missed the earlier instalment, start with site classification before the slab detail.
The low side is not one support category
Clause 4.2.6 directs you back to different parts of 4.2.5 depending on the element. The distinction is deliberate.
Slab panels follow 4.2.5(a).
Edge beams have the support alternatives set out in 4.2.6(b).
Edge beams not connected to the slab, pad footings and strip footings follow 4.2.5(c).
Cuts into natural ground must also follow Part 3.2.
The practical consequence is simple: a fill arrangement acceptable beneath the panel does not automatically establish the support beneath the edge beam or a separate footing. Identify the element before carrying an assumption across the drawing. Read clauses 4.2.5 and 4.2.6 together.
Four edge-beam alternatives, not four site shortcuts
Clause 4.2.6(b) identifies four alternatives:
Controlled-fill support. This follows 4.2.5(b), including its conditions, and corresponds to Figure 4.2.5 Option 1.
Deepened edge beams or bulk piers designed to AS 3600. This corresponds to Figure 4.2.5 Option 2. The reference to design matters. A site decision to add a pier is not the documented solution.
An edge beam deepened under AS 2870 to reach natural soil. The bearing capacity must meet 4.2.5(b), with Figure 4.2.5 Option 3 illustrating the arrangement.
An edge beam stepped in accordance with AS 2870. A change in level is part of the solution, not permission to improvise its geometry or reinforcement.
These are summaries, not complete specifications. The referenced Standards and the project design still do the work that a short article cannot. See 4.2.6(b) and Figure 4.2.5.
For the controlled-fill alternative, look beyond the neat surface. Check the fill records and the required support extent. For a deepened solution, check the founding level and the connection to the current design. For a stepped solution, check that everyone is working from the same detail and revision.
Those are BuildCompass coordination prompts. They are not additional NCC clauses or substitutes for the required assessment.
A stepped strip footing has its own provision
Do not confuse an edge beam stepped under 4.2.6(b)(iv) with the stepped strip footings addressed by 4.2.7.
Clause 4.2.7 permits a horizontal footing base, a base slope no steeper than 1:10, or stepping using a method shown in Figure 4.2.7. That ratio concerns the footing base. It is not a blanket approval for a property's slope, a batter or a retaining wall.
Figure 4.2.7 shows four methods with different geometry and reinforcement arrangements. Read the complete figure, including its dimensions. Do not lift the 200 mm step annotation from one method and treat it as the universal rule. Method D specifically addresses a step greater than 200 mm, subject to the other conditions shown.
This is a good place to slow down. A single number can be memorable and still be an incomplete specification. Read 4.2.7 and its figure.
Before the change in level disappears under concrete
Bring four things to the same conversation:
The current site report and footing drawings, with their revisions and limitations.
The actual locations of natural ground, fill, cuts and changes in level.
The documented support solution for each relevant element.
The records, clarification and inspections needed to connect that solution to the work.
If excavation exposes something different from the assumed ground, describe the discrepancy by location and obtain the appropriate project-specific response. Do not substitute extra depth, extra concrete or an unplanned pier for that response.
For builders, this helps connect set-out and excavation to the designed support. For trades, it makes the relevant detail and revision easier to identify. For designers and consultants, it focuses the clarification request. For homeowners, it provides better questions to ask, not an instruction to inspect an unsafe excavation or approve a pour.
A concrete booking is a programme milestone. It is not a substitute for a resolved support detail.
Learn the distinction, then use the right documents
Explore the free BuildCompass learning catalogue for the companion lesson once released and the earlier Part 4 modules. Subscribe to Industry Insights and The Friday Detail for the next instalment.
This article uses NCC 2022. Confirm the edition, amendment, state or territory variations, approval conditions and transition arrangements applying to the project. For example, NSW guidance identifies NCC 2022 Amendment 2 as current in NSW and announces NCC 2025 adoption on 1 May 2027. That is not a nationwide adoption statement.
We are completing the NCC 2022 learning sequence first. NCC 2025 updates will be reviewed separately afterwards.
General education only. Not project-specific structural or geotechnical advice, certification or permission to proceed.
Sources and attribution
ABCB Housing Provisions 2022, Part 4.2: clauses 4.2.1, 4.2.5, 4.2.6 and 4.2.7; Figures 4.2.5 and 4.2.7. Cross-checked against the owner-supplied ABCB Housing Provisions Standard 2022 PDF, 1 May 2023, pages 42 and 47 to 49.
NCC 2022 Volume Two, Part H1: H1D4 and its application limits.
NSW Government, how to comply with the NCC: edition and jurisdiction guidance, checked 8 October 2026.
The National Construction Code 2022 was provided by the Australian Building Codes Board under the CC BY 4.0 licence. This article paraphrases selected provisions and adds BuildCompass commentary. No ABCB endorsement is implied. Referenced Australian Standards are not reproduced.
