Excavation and Shoring Requirements for Building Sites

What This Requirement Covers

Excavation and shoring requirements set out how soil and siteworks must be carried out before and during construction to protect structural stability, prevent collapse of trenches and excavations, protect adjoining properties and services, and provide a safe working environment. These requirements cover the depth and preparation of excavations for footings and slabs, the design and construction of temporary shoring and retaining work, the treatment of exposed faces and batters, and measures for drainage and erosion control. They exist to manage geotechnical risk, protect occupants and neighbouring land, and ensure foundations are formed on suitable bearing material.

These requirements apply to designers, builders, site supervisors, and certifiers engaged in building work across all building classes. For residential Class 1 and 10 work the ABCB Housing Provisions and NCC Volume Two provide specific Deemed-to-Satisfy provisions for excavation and footings. For commercial, multi-residential, and other Class 2-9 buildings the relevant provisions appear in NCC Volume One and referenced Australian Standards and structural design clauses. Work that affects stability of adjoining property, public land, or services will often trigger more stringent local conditions and may require certified designs by an engineer.

Key Requirements

1. Excavation shape and base: Excavations for footings should be clean cut with vertical sides wherever possible and bases should be generally level. For flat sites the base may slope not more than 1:40 to provide drainage; for sloping sites the base may follow the slope at an angle not more than 1:10, as specified in ABCB Housing Provisions (NCC Volume Two, Section 4.2.3 / H1D4 references). (ABCB Housing Provisions Standard 2022, NSW 4.2.3)
2. Minimum depth on loose sand or erosion-prone sites: Where sites have loose sand or are subject to wind or water erosion, the depth from finished ground level to the base of footings must be not less than 300 mm. (ABCB Housing Provisions Standard 2022, Section 4.2.3)
3. Removal of unsuitable material: Footing excavations must be free of loose earth, tree roots, mud and debris; topsoil and organic material must be removed from under footings. (ABCB Housing Provisions Standard 2022, Section 4.2.3)
4. Filling beneath slabs: Filling under in-ground concrete slabs must be controlled fill or rolled fill with specified compaction and material limits. Examples from the Housing Provisions: sand controlled fill up to 800 mm compacted in layers not more than 300 mm; clay fill up to 400 mm compacted in layers not more than 150 mm. Sand used must meet compaction blow-counts (AS 1289 test) where specified. (ABCB Housing Provisions Standard 2022, Section 4.2.4)
5. Retaining walls and earth-retaining structures: For retaining walls between 800 mm and 15 m in height the requirements of AS 4678 (Earth-retaining structures) apply; design must address permanent loads, backfill, surcharge loads and drainage. NCC Volume Two explanatory material references AS 4678 for earth-retaining structures. (NCC 2022 Volume Two, explanatory information)
6. Temporary shoring and trench support: Temporary shoring and propping of excavations must be designed to resist lateral loads from soil and adjacent structures, and to provide safe access/egress and edge protection where required by occupational safety regulations. Design should be by a suitably qualified engineer where depth, soil conditions, or proximity to structures create risk. Relevant structural design clauses appear in NCC Volume One and referenced standards such as AS 4100 for steelworks and general structural practice, and AS 4970 where tree protection and site work interfaces apply.
7. Site classification and footing design: Footing and slab design must follow the appropriate site classification as per AS 2870 for residential footings (Class A, S, M, H, E, P) or the structural design requirements in NCC Volume One for non-residential classes. NCC Volume Two (H1D4) allows using AS 2870 or Section 4 of the Housing Provisions where conditions are met. (NCC Volume Two, H1D4; ABCB Housing Provisions Standard 2022)
8. Drainage and erosion control: Excavations must be protected from water accumulation and erosion during and after works; bases may be sloped to drain, and temporary diversion works and silt control must be provided to protect neighbouring properties and foundations (refer NCC Volume Two H1D3/H1D4 explanatory notes and local council conditions).
9. Relevant standards and references: Key Australian Standards and references commonly applied to excavation and shoring include AS 4678 (Earth-retaining structures), AS 2870 (Residential slabs and footings), AS 3700 (Masonry), AS 4100 (Steel structures) for structural design elements, AS 1289 (soil testing methods), AS 4970 (Protection of trees on development sites) where applicable, and AS 3798 (Guidelines on earthworks for commercial and residential developments). Cite NCC documents directly: NCC Volume Two (ABCB Housing Provisions) for Class 1/10 excavation rules and NCC Volume One for Class 2-9 structural requirements.
10. Design documentation and certifier expectations: Where excavation or shoring affects structural stability or adjoining land, certifiers will expect engineering drawings with design loads, shoring details, drainage and sequencing, and geotechnical reports stating allowable bearing capacity in kPa and recommended founding depths in mm or m (per AS 2870 or project-specific geotechnical advice).

Residential vs Commercial

1. Residential (Class 1 and Class 10): The ABCB Housing Provisions (NCC Volume Two) provide Deemed-to-Satisfy measures for excavation for footings and slabs, including the vertical sides, base slopes (1:40 flat, 1:10 on slopes), 300 mm minimum footing depth on loose sand, and controlled fill compaction requirements. Site classification by AS 2870 is central to footing design for typical houses and associated Class 10 structures. Where conditions fall outside the Housing Provisions (e.g., complex slope, expansive soils, retaining over 800 mm) a structural or geotechnical engineer’s design is required.
2. Commercial (Class 2-9): Excavation and shoring for multi-storey, commercial and industrial buildings rely on NCC Volume One structural provisions and referenced Australian Standards, and frequently require site-specific geotechnical investigations and engineered temporary works designs. Retaining walls and earthworks above 800 mm must follow AS 4678, and deeper excavations, propping systems and ground anchors must be designed with loadings expressed in kPa and specified member capacities per structural standards such as AS 4100. Commercial projects have a lower tolerance for Deemed-to-Satisfy simplifications and generally require certified engineering designs and detailed documentation.

Exceptions and Exemptions

1. Small shallow excavations that do not affect footings, foundations, or adjoining structures and that meet local building and occupational safety exemptions may not need engineered shoring designs; however, this varies by state and local authority and by depth and location.
2. Where alternative Performance Solutions are prepared and verified, compliance can be achieved outside Deemed-to-Satisfy provisions. Any Performance Solution must be supported by appropriate testing, calculations and expert reports (NCC Assessment Methods). (NCC Volume Two, H1P1 explanatory guidance)
3. In some low-risk residential scenarios the Housing Provisions permit using prescriptive footing solutions (Section 4) rather than AS 2870 provided site classification and dimensional limits are satisfied. (NCC Volume Two, H1D4)
4. State schedules may impose additional prescribed conditions (for example, NSW requires shoring adequacy as a condition of development consent for certain works). Always check local schedule and consent conditions. (ABCB Housing Provisions Standard 2022 notes)

State and Territory Variations

1. New South Wales: NSW inserts specific provisions into the ABCB Housing Provisions. Excavation for footings is explicitly required to be clean cut with vertical sides where possible, and NSW notes that shoring and adequacy of excavation works may be a prescribed condition of development consent. NSW also provides localised H1D4 and excavation clauses in the Housing Provisions. (ABCB Housing Provisions Standard 2022, NSW 4.2.3)
2. Other jurisdictions: While the NCC and ABCB Housing Provisions set the national baseline, each state and territory has schedules (Schedules 4-12 in NCC Volume One and state variations in the Housing Provisions) that can modify, add or delete provisions relevant to excavation, shoring and siteworks. Local councils may also require additional engineering designs, site-specific sediment and erosion control plans, or requirements for protection of adjoining structures. Always check the relevant state schedule in NCC 2022 Volume One and local planning/development consent conditions.

Practical Compliance Tips

1. Obtain a geotechnical report early - a site classification (AS 2870) and allowable bearing pressures in kPa will define founding depths and whether engineered shoring is required.
2. Keep excavations clean and to dimension - remove topsoil and organic material, maintain vertical faces where possible and keep bases level within the allowed slope limits (1:40 flat, 1:10 on slopes) to avoid unexpected settlement or footing removals.
3. Engage an engineer for anything over 800 mm or near adjacent structures - retaining walls, deep excavations, unusual site conditions or loads generally require AS 4678-compliant designs and certified shoring drawings.
4. Document temporary works and sequencing - provide certifiers with shoring drawings, design loads in kPa, bracing details and a construction sequence to demonstrate stability during works.
5. Control water and erosion - slope bases to drain, use temporary diversion drains and silt fencing; waterlogged excavations reduce bearing capacity and increase shoring loads.
6. Follow compaction requirements for fill - use controlled or rolled fill with layer thickness limits (300 mm for sand, 150 mm for clay where applicable) and perform compaction testing per AS 1289.
7. Check state schedules and consent conditions - verify whether your state or local council places prescribed conditions on shoring or excavation adequacy (for example, NSW development consents frequently do).

Sources: NCC 2022 Volume Two - ABCB Housing Provisions (H1D3, H1D4, Section 4.2.3 and 4.2.4), ABCB Housing Provisions Standard 2022 (NSW variations), and referenced Australian Standards including AS 4678, AS 2870, AS 4100, AS 3700, AS 1289 and AS 3798.