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NZ Building Code · StructuralFooting sizes for NZ buildings, in plain English
How to size timber-pile, strip, slab-edge and pad footings under NZS 3604 and B1/AS1 — where the numbers come from and what changed under Amendment 11.
Footings are what spread the load from your piles, walls and posts into the ground — get the size or the steel wrong and it’s a fail at inspection or worse. This is a plain-English map of how footings get sized in NZ: which come off an NZS 3604 table, which don’t, and what the current B1/AS1 amendment changed.
Sizing a timber-pile footing
Pile-footing plan sizes for timber-framed buildings come from the footing tables in NZS 3604:2011 §6 — we don’t reproduce those rows here.
- Work out your pile load and the number of storeys.
- Read the footing size off NZS 3604:2011 Table 6.1 for that pile load and storeys, using Table 6.4 for the loaded dimension.
- Use the correct row — heavier loads (two-storey, tile roof) need a larger footing.
Footings are 17.5 MPa concrete minimum (more in coastal zones). Always read the size for your pile load and number of storeys off your licensed copy of the standard.
Footing types NOT sized from an NZS 3604 pile table
These come from B1/AS1 or specific engineering, not the pile-footing tables:
- Strip footing (NZS 4229 masonry) — for a concrete masonry wall. 2× D12 longitudinal bars; 25 MPa coastal or 17.5 MPa inland. Under B1/AS1 Amendment 11 the single-D12 option was deleted. Strip dimensions per NZS 4229 — read them off your copy of the standard.
- Slab edge footing (NZS 3604 §7.5) — for a slab on ground. 2× D12 bars plus R10 starters, tied to the slab mesh; 17.5 MPa inland, 20 MPa Zone C, 25 MPa Zone D. Edge-thickening dimensions per NZS 3604 §7.5.
- Pad footing (engineered post) — for a single point load such as a portal frame. No NZS 3604 prescription; always engineered with a PS1, at 25 MPa. Size and reinforcing come from the engineer’s design.
What B1/AS1 Amendment 11 changed
Amendment 11 is current, and it tightened wall footings under NZS 3604:
- Wall footings now require 2× D12 longitudinal bars — the single-D12 option was deleted (Figures 7.13(A), 7.14(A), 7.15(A) and 7.16(A) removed).
- 30mm cover to reinforcing.
- Slab reinforcing must be tied to the foundation reinforcing.
Concrete cover to reinforcing
Cover depends on exposure — more exposed and aggressive environments need more:
- 30mm — standard residential.
- 40mm — Zone C exposed.
- 50mm — Zone D coastal or aggressive environment.
- 40mm clear cover to the face of formwork, measured to the nearest bar.
Plain-English guide, not advice. This page helps you understand and navigate the rules — it is general information, not design, engineering or consent advice, and it does not reproduce the copyrighted tables of NZS 3604 or any Standard. Always check the current Standard or Acceptable Solution and your BCA, and use a suitably qualified LBP, engineer or QS where it matters.
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Common questions
Where do timber-pile footing sizes come from?
From the footing tables in NZS 3604:2011 §6 — read the size for your pile load and number of storeys off Table 6.1, using Table 6.4 for the loaded dimension. Use your licensed copy of the standard; heavier loads such as two-storey or tile roof need a larger footing.
What concrete strength do footings need?
Timber-pile footings are 17.5 MPa concrete minimum, with more in coastal zones. Other types vary: strip footings are 25 MPa coastal or 17.5 MPa inland; slab edge footings are 17.5 MPa inland, 20 MPa in Zone C and 25 MPa in Zone D; engineered pad footings are 25 MPa.
What did B1/AS1 Amendment 11 change for wall footings?
Wall footings under NZS 3604 now require 2× D12 longitudinal bars — the single-D12 option was deleted and Figures 7.13(A), 7.14(A), 7.15(A) and 7.16(A) were removed. Cover is 30mm, and slab reinforcing must be tied to the foundation reinforcing.
How much concrete cover to reinforcing is required?
30mm for standard residential, 40mm for Zone C exposed, and 50mm for Zone D coastal or aggressive environments. Clear cover to the face of formwork is 40mm, measured to the nearest bar.
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