NZS 3604 explained
NZS 3604 Timber-framed buildings is the Standard that lets most New Zealand houses be built without an engineer. It is cited by B1/AS1, which makes following it an Acceptable Solution. It is also a paid Standard whose tables are copyright, and this page explains what it covers and where its scope ends rather than reproducing it.
Where it sits in the system
The Building Act 2004 sets the law. The New Zealand Building Code, Schedule 1 to the Building Regulations 1992, sets performance requirements in clauses such as B1 Structure, D1 Access Routes and F4 Safety from Falling. The Code says what a building has to achieve, never how.
Acceptable Solutions and Verification Methods are the how. Build to one and the building consent authority must accept it as complying. B1/AS1 cites NZS 3604, which is why a house framed to NZS 3604 is accepted without structural calculations.
You are never obliged to use it. The alternative is an alternative solution, which means demonstrating compliance another way. That is what Specific Engineering Design is, and it is how anything outside the Standard gets consented.
What it covers
- Foundations and subfloor framing, including piles and bearers.
- Floor framing, joists and flooring.
- Wall framing, studs, plates, lintels and bracing.
- Roof framing, rafters, purlins and trusses within its scope.
- Fixings, connections and the bracing demand and capacity system.
- Durability requirements for timber treatment.
Scope is the thing that catches people
NZS 3604 applies to buildings within defined limits on height, floor area, wall length, roof mass and wind zone, among others. Step outside any one of them and the whole building does not simply fall out of the Standard, but that element needs engineering.
The limit that catches the most people is wind zone. Above Extra High the site needs Specific Engineering Design. The second is roof mass, because a change from long run steel to concrete tile late in a design puts loads through framing that was sized for something lighter.
Bracing is where it gets misunderstood
The bracing system works on demand and capacity. The building generates a bracing demand from its wind zone, earthquake zone, shape and mass. Bracing elements provide capacity, measured in bracing units. Capacity has to meet demand, and it has to do so in both directions and distributed sensibly through the building rather than concentrated at one end.
The common failure is not a shortfall in total bracing units. It is distribution: enough units in the building, badly placed, with a long unbraced wall doing nothing. A bracing plan is a real design document, not a sum.
What we can give you instead
Two things. First, the free loaded dimension calculator, which works out the geometry a span table asks for. Second, the pointer to the free BRANZ Lintels and Beams calculator, which will size the member. Between them you get an answer without anyone infringing a copyright.
For everything else, buy the Standard. A building consent application that relies on it is worth the cost of the document.
Keep the consented drawings and the site in sync
Built Simple stores the plans, the inspection records and the photos against the job. Free to start.
Frequently Asked Questions
What is NZS 3604? NZS 3604 Timber-framed buildings is the New Zealand Standard that allows most houses to be built without specific engineering design. It is cited by B1/AS1, which makes compliance with it an Acceptable Solution under the Building Code.
Is NZS 3604 free to download? No. It is a paid Standard from Standards New Zealand. Section 27(1C) of the Copyright Act 1994 expressly preserves copyright in New Zealand Standards even where legislation refers to them, so being cited by B1/AS1 does not make it free.
Do I have to use NZS 3604? No. It is one route to compliance. The alternative is an alternative solution, usually Specific Engineering Design by a chartered professional engineer, which is what anything outside its scope needs anyway.
When does a house fall outside NZS 3604? When it breaches any of the scope limits, which include height, floor area, wall length, roof mass and wind zone. Above the Extra High wind zone you need Specific Engineering Design.
What are bracing units? The Standard expresses bracing as demand and capacity in bracing units. The building generates a demand from its wind and earthquake zones, shape and mass, and bracing elements supply capacity. Distribution matters as much as the total.
Related calculators and guides
Sources
- Building Act 2004.
- New Zealand Building Code, Schedule 1 to the Building Regulations 1992.
- building.govt.nz, for B1/AS1 and the Acceptable Solutions.
- Copyright Act 1994, sections 27(1)(c) and 27(1C).
