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NZ Building Code · Standards & CodesThe 2025 Building Code update: what actually changed
A plain-English rundown of the 2025 Building Code update — the reissued Acceptable Solutions, the new Building Product Specifications, and the myth that NZS 3604 changed.
The 2025 Building Code update reissued the Acceptable Solutions and Verification Methods and introduced the first edition of the Building Product Specifications (BPS). The most important thing to get straight: NZS 3604:2011, the timber-framing standard, did not change — what changed is the Acceptable Solution (B1/AS1) that cites it, and how products get specified.
The distinction people get wrong
Most of the confusion comes from mixing up the standard with the Acceptable Solution that points to it. They are two different documents.
- NZS 3604:2011 is the standard — the span tables, bracing and fixings. It is still the current edition.
- B1/AS1 is the Building Code Acceptable Solution that cites NZS 3604 “with modifications.” This is the document that got reissued as a 2nd edition.
So when someone says “the 3604 changes,” they almost always mean the B1/AS1 modifications plus the 2025 reissue — not the standard’s tables, which have not moved.
What actually changed on 28 July 2025
The reissued Acceptable Solutions and Verification Methods took effect on 28 July 2025, with one exception: H1 comes into force on 27 November 2025.
- B1/AS1 2nd edition — republished as a clean, standalone document with clearer structure, updated terminology and corrected cross-references. It still cites NZS 3604:2011 for timber-framed buildings up to 10 m or 3 storeys on good ground, but now also points to the BPS for some product choices.
- Building Product Specifications (BPS) 1st Ed — a new central document, issued under Building Act s25B, that lists the product standards an Acceptable Solution or Verification Method relies on (manufacture, testing, durability, installation). It is cited by an AS/VM and is never used on its own.
- 3604 + BPS together — when you build to NZS 3604 you now also check BPS Section 3.5 (Timber) for the alternate and accepted product specs it adds: timber durability and treatment, and wall-bracing ratings. The 3604 tables still drive the structure; the BPS governs the products that satisfy them.
Other reissued and new editions
Several other clauses were reissued at the same time:
- B1/VM2 — geotech.
- B2/AS1 3rd ed — durability; treatment detail moved to the BPS.
- C/AS1–2 + C/VM2 — fire; test methods centralised in the BPS.
- E2/AS1 4th ed — external moisture; same layout, renumbered.
- G4/AS1 5th ed — ventilation.
- H1/AS1 6th ed — the Schedule method is removed, leaving Calculation and Modelling only; in force 27 November 2025.
How B1/AS1 modifies NZS 3604
This is the part that catches people out: B1/AS1 sets stronger foundation rules than the base standard, and they live in the Acceptable Solution rather than in the 3604 tables, so they are easy to miss.
After the Canterbury earthquakes the Department added tougher slab and foundation rules, then extended them to all of New Zealand on 1 August 2011. In practice this means:
- Foundations must be tied to the concrete slab with reinforcing steel.
- A minimum 400×200 deep footing with 2× D12 longitudinal bars — the older single-D12 detail was deleted.
- 25 MPa concrete on the coast.
Because this sits in B1/AS1 and not in the NZS 3604 tables, it is a common thing to overlook.
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
Did NZS 3604:2011 change in the 2025 update?
No. NZS 3604:2011, the timber-framing standard with the span tables, bracing and fixings, did not change and is still the current edition. What changed is B1/AS1 — the Acceptable Solution that cites NZS 3604 “with modifications” — which was reissued as a 2nd edition, along with the new Building Product Specifications.
When does the 2025 Building Code update take effect?
The reissued Acceptable Solutions and Verification Methods took effect on 28 July 2025. The one exception is H1/AS1 6th edition, which comes into force on 27 November 2025 — that edition removes the Schedule method, leaving Calculation and Modelling only.
What are the Building Product Specifications (BPS)?
The BPS is a new central document, first edition, issued under Building Act s25B. It lists the product standards an Acceptable Solution or Verification Method relies on — covering manufacture, testing, durability and installation. It is cited by an AS/VM and is never used on its own. When you build to NZS 3604 you now also check BPS Section 3.5 (Timber) for timber durability, treatment and wall-bracing ratings.
What foundation rules does B1/AS1 add on top of NZS 3604?
After the Canterbury earthquakes, tougher slab and foundation rules were extended to all of New Zealand on 1 August 2011. Foundations must be tied to the concrete slab with reinforcing steel — in practice a minimum 400×200 deep footing with 2× D12 longitudinal bars (the older single-D12 detail was deleted) and 25 MPa concrete on the coast. These rules sit in B1/AS1, not the NZS 3604 tables, so they are easy to miss.
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