How deep and how big are pile footings under NZS 3604?
Published · Updated · By Sai Nath
BRANZ’s guide to NZS 3604:2011 puts an ordinary timber pile (125 × 125 mm square or 140 mm round) on a concrete footing at least 200 mm deep, with 100 mm of concrete under the pile. Braced piles go 450 mm deep and anchor piles 900 mm, on good ground of 300 kPa; Table 6.1 sets the footing size.
Which standard sets footings for a timber house or deck?
Building Code clause B1 Structure. Its Acceptable Solution, B1/AS1 2nd edition (in force since 28 July 2025), lets you use NZS 3604:2011 Timber-framed buildings for houses and small buildings, with changes to its definitions, bracing, timber piles, decks and slabs (B1/AS1 2.3.1.1). Foundations and subfloor framing are NZS 3604 Section 6. MBIE has paid for NZS 3604:2011 to be free to download since 2019, so read the tables in your own copy.
This page quotes no NZS 3604 table. The figures come from two free BRANZ explainers that cite the clauses: Bulletin 560 Pile foundations (May 2013) and the worked deck in Designing a deck (February 2013). Both predate B1/AS1’s 2nd edition, so check each clause in your copy. A revised NZS 3604 was out as a draft for comment from 29 June to 22 September 2026; Standards New Zealand says the draft is not for building, so the 2011 edition, as modified by B1/AS1, still applies.
Pile types and depths at a glance
| Pile | What it does | Depth and footing | Height above ground |
|---|---|---|---|
| Ordinary timber | Carries the weight only | Concrete footing at least 200 mm deep, pile 100 mm into it, 100 mm of concrete under the pile | 300 mm min (150 mm with a DPC under the bearer), 3000 mm max |
| Driven timber | Carries the weight only | No footing: driven 900 mm into gravel or 1200 mm into other soils, or until it reaches driving resistance; 3600 mm long at most | 2700 mm max |
| Driven timber, cantilevered | Weight, plus bracing in both directions | As for driven piles | 1200 mm max |
| Braced | Weight, plus bracing along the brace | Encased in concrete 450 mm deep, or driven | 3000 mm max for timber |
| Anchor | Weight, plus bracing in both directions | Encased in concrete 900 mm deep, including 100 mm under the pile | Top fixing 600 mm max |
Source: BRANZ Bulletin 560, Table 1 and sections 4.1 to 4.8, which point to NZS 3604 Section 6, clause 6.6 for driven piles. Timber piles meet NZS 3605, are treated to H5 and are at least 140 mm across if round or 125 × 125 mm if square sawn (4.1.2, 4.1.4); B1/AS1 2.3.5.1 adds that timber piles used under NZS 3604 must also meet subsection 2.1.2 of MBIE’s Building Product Specifications. Footing concrete is ordinary grade, 17.5 MPa at least (4.3.5).
What is good ground?
NZS 3604 only covers buildings on good ground. B1/AS1 1.2.1.1 defines it as soil or rock that can permanently take an ultimate bearing pressure of 300 kPa, which is 100 kPa allowable with a factor of safety of 3.0. It leaves out:
- compressible ground such as topsoil, soft clay you can mould in your fingers, and loose gravel with obvious voids;
- expansive soils, with a liquid limit over 50% and a linear shrinkage over 15%;
- ground that could foreseeably move 25 mm or more, for any of the reasons B1/AS1 lists.
The comment under it gives the site test: with a dynamic cone (Scala) penetrometer to NZS 4402 Test 6.5.2, at least 5 blows per 100 mm down to twice the footing width below the footing, and 3 blows per 100 mm deeper than that. Ground that isn’t good ground puts a piled foundation outside NZS 3604, and it needs specific engineering design. Check with your building consent authority what testing it wants to see.
How big is the footing?
NZS 3604 Table 6.1 sets the plan size of a pile footing from the pile spacing and the load it carries (BRANZ Bulletin 560, 4.3.4). BRANZ’s worked deck shows the result for one case: bearers spanning 1.3 m between piles and joists spanning 2.1 m give ordinary pile footings 260 mm across and at least 200 mm deep (Table 6.1 and Figure 6.2), and braced pile footings 400 mm across and at least 450 mm deep (clause 6.8.1.1). Longer spans need bigger footings, so take the size from Table 6.1 or your plans, not from this example.
Worked example: concrete for 16 pile footings
A deck on 12 ordinary piles and 4 braced piles, using the footing sizes from BRANZ’s deck as the inputs. Each hole is a cylinder: π × radius² × depth.
- Ordinary footing, 260 mm across and 200 mm deep: π × 0.13² × 0.20 = 0.0106 m³. Twelve of them: 0.1274 m³.
- Braced footing, 400 mm across and 450 mm deep: π × 0.20² × 0.45 = 0.0565 m³. Four of them: 0.2262 m³.
- Together: 0.1274 + 0.2262 = 0.3536 m³, or 0.3890 m³ with 10% for waste.
- The piles take up some of it. A 140 mm round pile sits 100 mm into each ordinary footing, π × 0.07² × 0.10 = 0.0015 m³, and 350 mm into each braced one (450 mm less the 100 mm under it), π × 0.07² × 0.35 = 0.0054 m³. That is 12 × 0.0015 + 4 × 0.0054 = 0.0400 m³, so the net is about 0.3136 m³, or 0.3450 m³ with 10%.
Holes rarely come out exactly to size. Measure what you dug before you order, because a hole 300 mm across instead of 260 mm holds a third more concrete.
Doing it in MeisterCalc
Open Home ▸ Concrete and choose Holes. Enter Diameter 260 mm, Depth 200 mm and Number of Holes 12: it shows Per Hole 0.0106 m³, Total 0.1274 m³ and Order (+10%) 0.1402 m³. Then enter Diameter 400 mm, Depth 450 mm and Number of Holes 4 for Per Hole 0.0565 m³, Total 0.2262 m³ and Order (+10%) 0.2488 m³. The two orders add up to 0.3890 m³. Concrete is free. It doesn’t take off the volume of the piles, and it doesn’t know NZS 3604 or size a footing: the diameter and depth are yours to type from Table 6.1 or the plans.
Before you dig
B1/AS1 2nd edition and NZS 3604:2011 were the current versions on 1 November 2026. Following them is one way to comply with clause B1, and your consented plans, your designer and your building consent authority decide the pile layout, bracing and footing sizes for your job. MBIE notes that structural work on a house is likely to be restricted building work, which a licensed building practitioner must carry out. For the deck above the piles, see joist spacing in New Zealand and barrier heights.
Sources
Checked on 1 November 2026. These pages explain the rules; the code itself, your plans and your council, building consent authority, building control body or certifier decide what a job needs.
- MBIE, Acceptable Solution B1/AS1 Structure, 2nd edition (PDF): effective 28 July 2025; 1.2.1.1 good ground and its comment on penetrometer testing; 2.3.1.1 NZS 3604 with modifications; 2.3.5.1 timber piles; Appendix A cites NZS 3604:2011 (checked 1 November 2026)
- MBIE, B1 Acceptable Solutions and Verification Methods: where MBIE lists the current B1/AS1 (checked 1 November 2026)
- MBIE, Using NZS 3604 Timber-framed buildings: NZS 3604 cited by B1/AS1 with modifications, good ground scope, free to download since 2019; structural work is likely restricted building work (last updated 26 January 2026) (checked 1 November 2026)
- Standards New Zealand, NZS 3604:2011 Timber-framed buildings: the free copy; Section 6 foundations, Table 6.1 footing sizes (checked 1 November 2026)
- BRANZ Bulletin 560, Pile foundations (May 2013, PDF): pile types, Table 1 depths and heights; 4.1.2 and 4.1.4 timber pile sizes and treatment; 4.3.1, 4.3.2, 4.3.4 and 4.3.5 footings; 4.7 braced and 4.8 anchor piles (checked 1 November 2026)
- BRANZ, Designing a deck (last updated 1 February 2013): worked deck: ordinary pile footings 260 mm by 200 mm deep (NZS 3604 Table 6.1, Figure 6.2), braced pile footings 400 mm by 450 mm deep (clause 6.8.1.1) (checked 1 November 2026)
- Standards New Zealand, DZ NZS 3604 consultation: draft revision open 29 June to 22 September 2026; not to be used for building (checked 1 November 2026)
Do the maths in MeisterCalc
MeisterCalc does the arithmetic behind these rules on an Android phone, with no signal needed: Stairs, Concrete and Check Square are free, and the other calculators come with Pro. It runs on Android 7.0 or later.