Pad footings: construction and sizing for residential builds
Pad footings for Australian residential builds: AS 2870 sizing, site classification, N20 minimum concrete, SL72 mesh, 100 kPa bearing, when engineering is required.
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Pad footings are isolated concrete pads that transfer concentrated point loads to the ground: deck posts, verandah columns, steel frame columns, and stump bases. On Class A and S sites, the ABCB Housing Provisions 2022 Part 4.2 provides DTS table sizes starting at 400 x 400 mm for a 10 m2 supported area, with a minimum 200 mm thickness and 100 kPa bearing capacity required. Minimum concrete is N20; reinforcement is SL72 mesh top and bottom. On Class M and above, or for any load not covered by the Housing Provisions tables, an engineer designs to AS 2870 directly. The two things that kill pad footing jobs: pouring into disturbed or inadequate bearing material, and undersizing the pad for the actual tributary area.
When you do this
Pad footings are used wherever a building transfers load through a concentrated point rather than a continuous wall or slab edge. Common residential applications:
- Deck and verandah posts: timber or steel posts for attached or free-standing decks and pergolas
- Stump bases: concrete stumps in raised subfloor systems, common in older VIC and QLD construction and new sloping-site builds
- Verandah and carport columns: steel or timber columns at corners and intermediate supports
- Steel column bases: where a structural steel column lands on the ground in residential construction
- Isolated masonry piers: on Class A and S sites (though strip footings complying with Part 4.2 clause 4.2.15 may be used instead of pad footings for masonry piers)
Pad footings are not used under continuous loadbearing walls. That application is strip footings. They are also not the base system for stiffened raft or waffle pod slabs; those use edge and internal beams integral with the slab.
Who’s involved
| Role | Responsibility |
|---|---|
| Builder | Sequence, compliance, hold point management |
| Concretor | Excavation, formwork (if needed), pour and finish |
| Engineer | Design on Class M+ sites or any non-standard load case; sign off on footing drawings |
| Certifier / Building Inspector | Pre-pour inspection hold point; verifies depth, reinforcement, bearing |
Steps
1. Confirm site classification and design basis
Before excavating, confirm the site class from the soil report. This determines which design path applies:
- Class A and S: ABCB Housing Provisions 2022 Part 4.2 DTS tables apply. No engineer required for standard load cases.
- Class M: Housing Provisions Part 4.2 applies for strip and raft systems, but check whether your specific pad footing configuration falls within the DTS tables. If not, engineer to AS 2870.
- Class H1, H2, E, P: Engineering under AS 2870:2011 required. No DTS pad footing path for reactive or problem sites (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2).
2. Determine pad size from the DTS tables (Class A and S sites)
For clad frame construction on Class A and S sites, Housing Provisions Table 4.2.13g sets minimum pad dimensions by effective supported area (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2):
| Effective supported area | Square pad (min) | Circular pad diameter (min) | Pad thickness (min) |
|---|---|---|---|
| 10 m2 | 400 x 400 mm | 500 mm | 200 mm |
| 20 m2 | 500 x 500 mm | 600 mm | 225 mm |
| 30 m2 | 600 x 600 mm | 750 mm | 250 mm |
Notes applying to these dimensions (Table 4.2.13g):
- Minimum bearing pressure: 100 kPa. If the natural soil cannot provide 100 kPa, engineering is required.
- On rock foundations, pad width or diameter may be reduced to half these values.
- Backfill around the footing must be manually rodded and tamped, or the pad thickness must be increased by 50 mm to account for disturbed bearing.
- For masonry piers, strip footings under Part 4.2 clause 4.2.15 may be substituted for the pad footing.
The effective supported area is the tributary area of floor or roof load being delivered through the column to the pad. Calculate this before sizing: underestimating the tributary area and selecting a too-small pad is the most common sizing error.
3. Confirm bearing material at depth
Excavate to the design depth and visually inspect the bearing material before pouring. Bearing material must be natural soil (not fill, not disturbed backfill) capable of supporting the minimum 100 kPa bearing pressure. Common site issues:
- Soft or loose soil at design depth: extend the excavation to firm natural bearing strata. The 100 kPa minimum bearing pressure is the floor; if the soil below is softer, the pad must go deeper or the design must change.
- Root zones: trees and large shrubs within the influence zone can leave voids or soft pockets. Remove all root intrusion before pouring.
- Service trenches: if a service trench runs under the pad location, the disturbed and re-compacted fill may not achieve 100 kPa. Relocate the pad or get an engineer’s advice.
- Loose sand on exposed or sloping sites: on loose sand or sites subject to wind or water erosion, the depth to the bottom of the footing must be not less than 300 mm below finished ground level (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2).
4. Set reinforcement
Standard reinforcement for DTS pad footings under the Housing Provisions is SL72 mesh, top and bottom (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2).
Concrete cover requirements (clause 4.2.11):
| Surface condition | Minimum cover |
|---|---|
| Unprotected ground (in contact with soil) | 40 mm |
| On a membrane in contact with ground | 30 mm |
| Internal surfaces | 20 mm |
| External exposure | 40 mm |
For pad footings under concentrated loads such as structural steel columns, the Housing Provisions require SL72 mesh reinforcement with a minimum 50 mm cover to the reinforcement.
Use bar chairs or purpose-made spacers to hold the mesh at the correct depth. Mesh lying flat on the ground before pour is a pre-pour inspection fail.
5. Clear the pre-pour inspection hold point
Pre-pour inspection is a mandatory hold point on most residential projects. The building inspector (certifier or council inspector) must sight and sign off:
- Pad dimensions (check plan area against design)
- Excavation depth and bearing material quality
- Reinforcement placement and cover
- Any stump embedment depth or holddown anchors
Do not pour before this hold point is cleared. Concrete over an uninspected footing is a locked-in defect that cannot be remedied without demolition.
6. Pour concrete
Minimum concrete grade under Housing Provisions clause 4.2.10: N20 (20 MPa compressive strength). In practice, most projects use N25 or N32, particularly on reactive or aggressive soil chemistry sites where durability matters. N20 is the DTS floor; your engineer or concrete supplier may specify higher (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2).
Pour sequence:
- Check formwork is secure (or sides of excavation are intact and stable)
- Place concrete in lifts, rod or vibrate each lift to eliminate voids
- Strike off to finished level
- Install holddown bolts, stump connection hardware, or column base plates while concrete is green, per the engineer’s details or manufacturer’s specification
- Cure: keep moist and protected for minimum 3 days before loading
7. Post-pour: stump and column connections
For stump systems (classic raised subfloor), the stump must be embedded into the pad not less than the greater of: 30% of the stump height above ground level, or 450 mm (verified 2026-05-10, ABCB Housing Provisions 2022 Part 4.2).
Concrete around embedded stumps must slope away from the stump and finish not less than 100 mm above finished ground level. This prevents moisture pooling at the stump base, which accelerates decay in timber stumps and corrosion in steel.
Tolerances and acceptance
Pad footing workmanship tolerances from the HIA Guide are pending HIA member access. [HIA-072]
Verifiable AS 2870 and Housing Provisions requirements:
| Check | Requirement | Source |
|---|---|---|
| Pad plan dimensions | Per DTS table or engineer’s drawings | HP Table 4.2.13g |
| Pad thickness | 200 mm minimum for 10 m2 case (DTS) | HP Table 4.2.13g |
| Bearing pressure | Not less than 100 kPa on natural soil | HP clause 4.2.5 |
| Concrete grade | N20 minimum | HP clause 4.2.10 |
| Cover to reo (to ground) | 40 mm minimum | HP clause 4.2.11 |
| Cover to reo (on membrane) | 30 mm minimum | HP clause 4.2.11 |
| Stump embedment | 30% of height above ground or 450 mm (greater of) | HP clause 4.2.13 |
| Stump concrete finishing level | Not less than 100 mm above finished ground level | HP clause 4.2.13 |
Documents needed
- Soil classification report confirming site class
- Engineer’s drawings (Class M and above, or any non-DTS case)
- Housing Provisions Part 4.2 tables (DTS path, Class A and S)
- Pre-pour inspection sign-off from certifier
- Concrete docket confirming grade and batch plant
- Holddown hardware installation record (for engineered connections)
Common holds
| Hold | Cause | Resolution |
|---|---|---|
| Pre-pour not cleared | Inspector not notified or site not ready | Notify certifier ahead. Do not pour until cleared. |
| Inadequate bearing at design depth | Soft, loose, or disturbed soil | Excavate deeper to firm natural strata; notify engineer if depth change is significant |
| Wrong reinforcement | SL72 substituted with incorrect mesh | Check mesh markings against spec before pour. |
| Insufficient cover | Bar chairs not used; reo placed direct on ground | Install chairs; re-inspect |
| Stump short-embedded | Stump length cut too short for required embedment | Requote; stump replacement before pour |
| Service trench conflict | Trench backfill under pad footprint | Relocate pad or engineer alternative; no pour on disturbed fill |
References
- 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 2870:2011 Residential slabs and footings (product page). https://store.standards.org.au/product/as-2870-2011 (verified 2026-05-10).
- Australian Building Codes Board, NCC 2022 Volume Two, Part H1 Structure. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h1-structure (verified 2026-05-10).
Related
- AS 2870:2011 residential slabs and footings, the standard covering site classification and all residential footing types
- Slab on ground construction, the full slab build sequence including pre-pour hold points and tolerances
- Footing, plain-English definition of residential footings
- Soil report (geotech), what a soil classification report covers and how to read the site class output
- Site classification, the process and output of classifying a residential site under AS 2870
- Stumped, raised subfloor systems using concrete or timber stumps common in VIC and QLD
See also
- NCC 2022 Volume Two, the residential building code framework
- Slab on ground, plain-English definition of a slab on ground
- Engineer’s details, the structural drawings issued for non-DTS footing design
- Reactive soil, plain-English explanation of reactive clay and its effect on residential foundations
- Stiffened raft slab, the most common residential slab type in Australia
- Waffle pod slab, the reactive-site slab alternative
- Concrete grade, N20, N25, N32 and what the grade means on site
Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency: confirm current Housing Provisions Part 4.2 table values and AS 2870:2011 edition status at Standards Australia.