Pier footings: bored piers, driven piles and screw piles for residential builds
Pier footings for Australian residential builds: bored piers, driven piles, screw piles, AS 2870 site classes H1/H2/E/P, depth to bearing strata, engineering required.
Ask Chalkline about this →TL;DR
Pier footings are deep foundations used when near-surface soils cannot carry residential loads: reactive Class H1, H2, E, and P sites, sloping blocks where bearing strata sit well below surface, and infill lots on uncontrolled fill. There are three types: bored piers (drilled in-situ concrete, most common), driven piles (pre-formed steel, concrete or timber, fast on granular soils), and screw piles (steel helical shafts rotated in without excavation, suited to tight access and reactive clay). All three fall outside the ABCB Housing Provisions 2022 DTS path: every pier footing system requires engineering under AS 2870:2011 Appendix G and AS 2159:2009. Get the soil report, get the engineer’s design, then build to it. The most common mistake is specifying a conventional footing system on a reactive site and discovering the mismatch at pre-pour inspection.
When you do this
Pier footings are used when a conventional strip, pad, or raft system cannot safely transfer residential loads to competent bearing strata. Common triggers:
- Reactive Class H1, H2, E, or P sites: the near-surface clay shrinks and swells with seasonal moisture change to a degree that exceeds what conventional slab and footing systems can accommodate. Piers bypass the reactive zone and anchor in stable sub-surface material.
- Sloping blocks: bearing strata can be several metres below surface level at the high side. Piers are driven to depth rather than stepping footings down the slope.
- Infill on poor or uncontrolled fill: sites where fill has been placed without controlled compaction may not achieve the bearing pressure required by DTS footing tables. Piers punch through fill to natural soil or rock below.
- Pier-and-beam subfloor systems: raised timber or steel subfloor frames in VIC, QLD, and sloping-site builds rest on piers rather than a slab. Each pier transfers the bearer loads to a separate bearing point.
- Steeply reactive sites with deep-seated movement: where the AS 2870:2011 Hs (depth of design suction change) value is large, piers must extend well below the moisture-active zone. On extreme reactive sites, this can push pier depths to 6 m or more.
Pier footings are not used where a stiffened raft, waffle pod slab, or conventional pad footing system covers the site class. Use piers only where the engineer specifies.
Who’s involved
| Role | Responsibility |
|---|---|
| Geotechnical engineer | Soil investigation, site classification, Hs determination |
| Structural / civil engineer | Pier design: type, diameter, depth, reinforcement, concrete grade |
| Builder | Sequence, hold point management, pier contractor engagement |
| Pier contractor (specialist) | Drilling, driving, or screwing piers to design depth and set |
| Certifier / building inspector | Pre-pour inspection hold point; verifies alignment, depth, reinforcement |
Pier types: bored, driven, and screw
Bored piers
Bored piers are the most common residential pier type. A rotary auger drills a cylindrical hole to design depth, a steel reinforcing cage is lowered in, and concrete is poured in-situ (verified 2026-05-10, EFA Piling, Bored Piers).
- Typical diameters: 300 mm, 450 mm, 600 mm (larger on heavy-load or rock sites)
- Typical residential depth: 2 m to 8 m depending on site class and soil profile
- Concrete grade: engineer-specified; N25 minimum is common in practice; N32 on aggressive soil chemistry sites or where durability class requires
- Reinforcement: a steel cage designed to the engineer’s specification, with cover chairs to maintain minimum cover to ground (typically 40 mm to 75 mm depending on exposure)
- Spoil: excavated material is brought to surface and must be disposed of; this adds cost and logistics on tight urban sites
- Noise and vibration: low; suited to urban infill and noise-sensitive sites
- Bearing set: drilled to design depth, then assessed by the engineer or inspector to confirm competent bearing material in the base before pouring (verified 2026-05-10, Owner Inspections: Bored Piers vs Driven Piles)
Bored piers must be installed to a depth where hard clay or other competent stratum can provide a bearing stress of at least 450 kPa at the base, or as specified by the engineer’s geotechnical assessment (verified 2026-05-10, Owner Inspections: Bored Piers vs Driven Piles).
Driven piles
Driven piles are pre-formed elements: steel H-piles, precast concrete, or timber, forced into the ground by impact hammer, hydraulic press, or vibratory driver.
- Best suited to: granular soils (sand and gravel) where displacement during driving achieves a tight bearing set; less suited to cohesive clay which can heave adjacent piles during driving
- Residential application: less common than bored piers in Australian residential work, but used on some pier-and-beam systems and for coastal or sandy-soil sites
- Speed: faster installation than bored piers where soil permits; no spoil to remove
- Noise and vibration: significant; impact hammers are disruptive in established residential areas and may trigger dilapidation survey requirements for neighbouring properties
- Timber piles: used in older stump-based subfloor systems in VIC and QLD; subject to decay risk in wet ground; consult engineer on treatment class
- Set confirmation: pile refusal (inability to drive further at target depth) confirms bearing; dynamic load testing may be specified (verified 2026-05-10, Owner Inspections: Bored Piers vs Driven Piles)
Screw piles (helical piles)
Screw piles are steel hollow sections with one or more helix plates welded to the shaft. A drive head on an excavator rotates the pile into the ground without excavation or spoil generation. The two terms, screw pile and helical pile, are used interchangeably in Australian practice (verified 2026-05-10, Blade Pile: Understanding AS 2159).
- Best suited to: reactive clay on H and E class sites; tight-access sites where a large drill rig cannot work; sloping blocks; deck, pergola, and outbuilding footings
- No spoil: the pile displaces rather than excavates soil, eliminating spoil removal
- Depth confirmation: torque monitoring during installation confirms bearing set: the measured installation torque correlates to the pile’s capacity. Drilling continues until design torque is achieved, not just design depth (verified 2026-05-10, Blade Pile: How Deep Should Screw Piles Go)
- Typical residential depths: 3 m to 6 m on stable ground; 6 m to 10 m on reactive clay; up to 12 m on loose coastal sand or poor fill (verified 2026-05-10, Blade Pile: How Deep Should Screw Piles Go)
- Corrosion protection: galvanised or epoxy-coated shaft required; engineer specifies protection class for the site’s aggressiveness
- Immediate load-bearing: can be loaded immediately after installation, unlike poured concrete piers which must cure before loading
All screw pile design and installation must comply with AS 2159:2009 (verified 2026-05-10, Blade Pile: Understanding AS 2159).
Steps
1. Obtain and read the soil report
Before any pier design can start, a soil classification report from a geotechnical engineer is required. The report provides:
- Site class under AS 2870:2011 (A, S, M, H1, H2, E, or P)
- Hs value (depth of design suction change): the depth to which reactive soils move seasonally. Pier depth must extend below this zone to reach stable, non-reactive material.
- Bearing capacity of sub-surface strata at various depths
- Aggressiveness classification of groundwater and soil chemistry (which drives concrete grade and corrosion protection selection)
The geotechnical report is the founding document for the pier engineer’s design. Without it, no pier system can be correctly sized.
2. Engage the structural engineer for pier design
Pier footings are engineering-designed elements. The ABCB Housing Provisions 2022 do not contain DTS provisions for bored piers, driven piles, or screw piles: Part 4.2 explicitly states that Class H, E, and P sites require reference to AS 2870 for design (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2).
The engineer’s design will specify:
- Pier type (bored, driven, or screw)
- Pier diameter or shaft size
- Design depth or set criterion (bearing pressure, penetration refusal, or installation torque)
- Concrete grade (bored piers) or shaft grade and helix geometry (screw piles)
- Reinforcing cage details (bored piers): bar diameter, spacing, cage length, and cover
- Corrosion protection (screw piles and driven steel piles)
- Connection to the structure above: ground beam, bearer, slab, or holddown bolt detail
- Number and layout of piers
Engage an engineer with residential geotechnical or foundation experience. The engineer must be licensed for structural design in the relevant state.
3. Engage a specialist pier contractor
Pier installation requires specialist plant: rotary auger rigs, pile hammers, or hydraulic drive heads. This work is not typically in scope for a general concretor. Engage a pier contractor with demonstrated experience in the relevant pier type and who carries appropriate structural works insurance.
The pier contractor works to the engineer’s design drawings. Any deviation from design depth, diameter, or set criterion must be referred to the engineer immediately, not resolved on site without approval.
4. Set out pier positions
Pier positions are set out from the engineer’s footing plan, referenced to the site survey. Position accuracy matters: piers that miss their design location shift load paths and can invalidate the structural design. Setting-out tolerance is typically within 25 mm of design location in plan, but confirm with the engineer.
Mark each pier position with a peg or paint spot. Check against the structural drawings before any drilling commences.
5. Install piers to design depth or set
Bored piers: auger to design depth. Remove spoil. Lower reinforcing cage, checking cover to all sides. Confirm bearing material at the base is competent (the engineer or inspector may attend to confirm). Pour concrete in one continuous operation. Protect the top of the pier from contamination while the concrete is still green.
Driven piles: drive to refusal or to the engineer’s set criterion (typically a specified penetration per blow count at final set). Record pile set data on site. Trim pile head to design cut-off level.
Screw piles: rotate into the ground using the drive head. Monitor installation torque continuously. Continue to design depth AND until design torque confirms adequate capacity. Record torque log for each pile. The installer must not stop short of design torque just because design depth is reached, if bearing resistance has not been confirmed.
6. Clear the pre-pour inspection hold point (bored piers)
For bored piers, a pre-pour inspection hold point must be cleared before any concrete is placed. The certifier or building inspector verifies:
- Pier location matches design
- Hole depth matches design
- Bearing material at base is competent (inspector may require the engineer to attend)
- Reinforcing cage is correctly positioned, with cover chairs in place
- No groundwater intrusion that could dilute the concrete mix
Do not pour concrete into an inspected hole until the hold point is cleared. This rule is the same as for pad and strip footings.
7. Connect piers to the structure above
Piers are structural elements only if they are correctly connected to the frame, ground beam, or slab they support. Common connection types:
- Holddown bolts or starter bars cast into the pier head during the pour: transfers uplift and lateral loads in addition to compression
- Base plate and anchor system on screw piles: the installer attaches a base plate to the pile head at cut-off level; the engineer specifies the bolt pattern
- Ground beam bearing on bored piers for pier-and-beam systems: the pier head is formed to level, and a reinforced ground beam bears on top
All connections must follow the engineer’s details. Do not improvise connection to the structure.
Tolerances and acceptance
Workmanship tolerances for pier footings from the HIA Guide to Materials and Workmanship are pending HIA member access. [HIA-078]
Verifiable AS 2870 and AS 2159 requirements:
| Check | Requirement | Source |
|---|---|---|
| Pier type | Bored, driven, or screw: engineer-specified | AS 2870:2011 Appendix G |
| Pier depth / set | To engineer’s design depth and/or set criterion | AS 2870:2011 / AS 2159:2009 |
| Concrete grade (bored piers) | Engineer-specified; N25 common minimum in practice | Engineer’s design |
| Reinforcement cover (bored piers) | Typically 40 mm to 75 mm to ground; engineer-specified | AS 2870:2011 / engineer’s design |
| Screw pile torque | Must reach design installation torque, not just design depth | AS 2159:2009 |
| Pier position | Typically within 25 mm of design location in plan; confirm with engineer | Engineer’s drawings |
| Pre-pour inspection | Mandatory hold point before bored pier concrete | State building regulations |
Documents needed
- Geotechnical report confirming site class, Hs, bearing capacity, and soil aggressiveness
- Engineer’s footing design drawings specifying pier type, number, diameter, depth, reinforcement, and connection details
- Pier contractor’s installation records: depth log, torque log (screw piles), set data (driven piles)
- Pre-pour inspection sign-off (bored piers)
- Concrete delivery docket confirming grade and batch plant (bored piers)
- Structural connection details and installation record
Common holds
| Hold | Cause | Resolution |
|---|---|---|
| No engineer’s design | Builder assumed DTS path covers the site | Engage engineer before breaking ground. No pier system is DTS-path. |
| Inadequate bearing at design depth (bored) | Competent stratum sits deeper than geotechnical report indicated | Extend pier depth; notify engineer immediately; revised design may be required |
| Screw pile stopped short of torque target | Obstruction, or design depth reached before target torque | Notify engineer; do not accept a pile that hasn’t confirmed bearing capacity |
| Pier position error | Incorrect set-out | If outside tolerance: notify engineer; may need additional pier or redesign of connection |
| Groundwater in bored pier hole | High water table or sub-surface flow | Use casing or grout injection; engineer to confirm; do not pour into a water-filled hole without approval |
| Driven pile heave | Displacement during driving heaves adjacent piles | Monitor pile head levels during driving; re-drive heaved piles or engineer to assess |
| Connection detail missing | Holddown bolts or base plates not installed before pour | Rectify before pour; if pier already poured without connection hardware, engineer must specify a retrofit detail |
References
- Standards Australia, AS 2870:2011 Residential slabs and footings (product page, Appendix G covers deep footings including bored piers, driven piles and steel screw piles). https://store.standards.org.au/product/as-2870-2011 (verified 2026-05-10).
- Australian Building Codes Board, ABCB Housing Provisions 2022, Part 4.2 Footings, slabs and associated elements. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/4-footings-and-slabs/part-42-footings-slabs-and-associated-elements (verified 2026-05-10).
- Standards Australia, AS 2159:2009 Piling: design and installation (product page). https://store.standards.org.au/product/as-2159-2009 (verified 2026-05-10).
- Blade Pile, Understanding AS 2159: The Australian Standard for Piling. https://bladepile.com.au/blog/understanding-as-2159-the-australian-standard-for-piling/ (verified 2026-05-10).
- Owner Inspections Australia, Bored Piers vs Driven Piles: Understanding the Difference. https://ownerinspections.com.au/articles/bored-piers-vs-driven-piles-understanding-the-difference (verified 2026-05-10).
Related
- AS 2870:2011 residential slabs and footings, the standard covering all residential footing types including the deep-footing design procedures in Appendix G
- Pad footings, isolated point-load footings for columns, stumps and posts on Class A and S sites
- Strip footings, continuous wall footings for loadbearing masonry and framed walls
- Soil report (geotech), what a soil classification report covers and how to read the site class and Hs output
- Site classification, the process and output of classifying a residential site under AS 2870
- Reactive soil, plain-English explanation of reactive clay and why it drives pier footing use in Australia
- Reinforcement (reo), reinforcing mesh and bar specifications for footing and slab systems
See also
- NCC 2022 Volume Two, the residential building code framework referencing AS 2870
- Footing, plain-English definition of residential footings
- Stiffened raft slab, the common engineered slab alternative on reactive sites
- Waffle pod slab, reactive-site slab alternative using polystyrene void formers
- Concrete grade, N20, N25, N32 and what the grade means on site
- Class P site, problem sites requiring engineering from AS 2870
Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency: confirm current AS 2870:2011 and AS 2159:2009 edition status at Standards Australia, and ABCB Housing Provisions 2022 Part 4.2 table values.