Ask a structural engineer why a particular connection detail was sized the way it was, and the answer almost always traces back to the same reference document sitting behind the calculations.
That reference is NZS 3404, the design standard behind almost every piece of structural steelwork built in New Zealand. It governs how structural engineers size steel members and connections, and it shapes the technical requirements that detailers and fabricators then have to work within. This article sets out what NZS 3404 actually covers, how it fits alongside New Zealand’s other structural standards and the Building Code, and what it means in practice for design, detailing, and fabrication on a real project.
Key Takeaways
- NZS 3404 is New Zealand’s steel structures design standard, cited within Verification Method B1/VM1 to help demonstrate compliance with NZBC Clause B1 Structure.
- Its scope covers the design, fabrication, erection, and modification of steelwork in buildings, bridges, crane support structures, and composite steel and concrete members.
- NZS 3404 does not work alone: NZS 1170 supplies the design loads, and AS/NZS 5131 governs fabrication and erection quality once design is complete.
- Accurate steel detailing carries NZS 3404-compliant design intent through to shop drawings and fabrication, and errors at this stage are a common source of rework.
- NZS 3404 is currently undergoing its first full revision since 1997, with a draft standard and a proposed new Part 3 on durability out for public consultation.
What Is NZS 3404?
NZS 3404 Steel Structures Standard is published by Standards New Zealand and is the primary design standard for structural steelwork in this country. It is currently structured in two parts. Part 1 sets out the technical requirements for the design, fabrication, erection, and modification of steel structures, largely using the limit state design method. Part 2 is a commentary that explains the reasoning behind Part 1’s provisions and how certain clauses should be applied.
Limit state design works by checking a structure against defined performance thresholds rather than applying a single blanket safety factor. An ultimate limit state check covers strength and stability, while a serviceability limit state check covers deflection and other in-service performance. This is what allows engineers to size steel sections efficiently while still keeping a demonstrable margin of safety.
The standard’s scope is broader than most people initially assume. Beyond typical multi-storey and industrial buildings, NZS 3404 applies to crane support girders, highway, railway, and pedestrian bridges, and composite steel and concrete beams and columns. A portal-framed warehouse, a car park structure, and a bridge overpass are all designed under the same underlying standard, even though the detailing, fabrication, and erection challenges differ considerably between them.
NZS 3404 and the Building Code Compliance Pathway
NZS 3404 is not legislation in itself, but it sits at the centre of how structural steel projects demonstrate compliance with the New Zealand Building Code. The relevant performance requirement is Clause B1 Structure, and the recognised route for meeting it is Verification Method B1/VM1, which sets out how the AS/NZS 1170 design actions standards and the relevant material-specific standards, including NZS 3404 for steel, are to be applied together.
It is worth remembering that compliance documents like B1/VM1 are reviewed periodically, and the version referenced on a project matters. MBIE published an updated second edition of B1/VM1 in 2025, and the transition period allowing the previous edition to still be used has now closed. It is a useful reminder that project teams should always confirm they are working from the current version of a compliance document rather than an older template.
Building consent authorities generally expect structural steelwork documentation, calculations, and shop drawings to demonstrate compliance with NZS 3404, or for the designer to justify an alternative method under section 19 of the Building Act. In practice, the great majority of steel structures in New Zealand are designed, detailed, and consented against NZS 3404, because it is the established and well-understood pathway.
NZS 3404 and the Standards It Works Alongside
NZS 3404 does not operate in isolation. A structural steel project in New Zealand typically draws on at least three connected structural steel standards, and understanding where each one applies helps explain why steelwork documentation looks the way it does.
Design Actions Under the NZS 1170 Series
Before a steel member can be designed under NZS 3404, the loads it needs to resist have to be established first. That is the role of the AS/NZS 1170 structural design actions series: Part 0 sets general principles, Part 1 covers permanent and imposed actions, Part 2 covers wind actions, and NZS 1170.5 sets out New Zealand-specific earthquake actions. NZS 3404 takes these design actions as an input, then provides the methodology for sizing members and connections to resist them safely.
Fabrication and Erection Under AS/NZS 5131
Once a member or connection is designed, how it is actually fabricated and erected is governed by a separate standard, AS/NZS 5131 Structural Steelwork – Fabrication and Erection. This standard introduces construction categories, a risk-based classification from CC1 to CC4 that sets the level of technical and quality assurance required for a given piece of steelwork, based on factors such as consequence of failure and structural complexity.
In practice, this means a structural engineer’s NZS 3404 design and a fabricator’s AS/NZS 5131 construction category need to be read together. A moment connection in a high-consequence structure will typically demand a higher construction category, with more rigorous inspection and testing, than a simple bracing connection in a low-rise building.
What NZS 3404 Means for Member and Connection Design
For structural engineers, NZS 3404 sets out the design rules for the full range of steel member types: tension members, compression members including buckling checks for columns, beams in bending, and members subject to combined actions. It also covers the design of connections, bolted and welded, which in many steel structures are the more complex design exercise of the two.
Given New Zealand’s seismic hazard, connection design deserves particular attention. NZS 3404 works alongside NZS 1170.5 to support capacity design principles, where connections and members are proportioned so that a structure’s more ductile elements can yield in a controlled way during a significant earthquake, while brittle failure modes are avoided. Getting this hierarchy right on paper is only half the job. It then has to be carried through accurately into the connection details that get drawn up and built, since a connection that looks compliant on a general arrangement drawing can still fail to reflect the design intent once bolt groups, weld sizes, and plate thicknesses are actually detailed.
From Structural Design to Shop Drawings: Why Detailing Accuracy Matters
The gap between a structural engineer’s NZS 3404 calculations and a fabricator’s cutting list is bridged by detailing. This is where connection types, bolt patterns, weld symbols, and member sizes are translated from a structural drawing into fully dimensioned, CAD-drafted shop drawings and, increasingly, coordinated 3D BIM models that fabricators can work from directly. For readers less familiar with what that process actually involves day-to-day, it’s worth understanding what steel detailing covers, since it goes well beyond simply redrawing the engineer’s design at a larger scale.
Detailing errors do not just cause delays on site. Common examples include:
- A missed clash between a beam and a duct, pipe, or cable tray
- A bolt group that does not physically fit within the section it is connecting to
- A weld specified without adequate shop or site access to actually run it
Any of these can mean the erected structure no longer reflects the connection design that was checked against NZS 3404 in the first place. This is why structural steel detailing is treated as a specialised discipline in its own right on most New Zealand projects, sitting between structural engineering and fabrication rather than being an extension of either.
NZS 3404 Is Currently Being Revised
NZS 3404 Parts 1 and 2 were originally published in 1997 and have not had a full revision since. That is changing. A draft revised standard has been prepared by a revision committee working under Standards New Zealand and released for public consultation, the first full rewrite of the design standard in almost three decades. The revision is looking at removing material now duplicated in other standards and technical specifications, simplifying the document, and updating provisions covering durability, retrofitting, repairability, inspection, fire, and seismic requirements.
Alongside the revised Parts 1 and 2, a proposed new Part 3 covering durability requirements for steel structures and components is also out for consultation. This effectively elevates what has previously been a standalone technical specification on corrosion protection into a full part of the NZS 3404 series, aligned with related standards covering protective coatings and galvanizing.
None of this changes what applies today. NZS 3404:1997 Parts 1 and 2 remain the current, cited edition until the revised standard is finalised and formally adopted into the Building Code compliance framework. Project teams working on longer-programme developments would still be well advised to keep an eye on the revision, since a structure consented today under the current standard could still be under construction once an updated version eventually takes effect for new projects.
Frequently Asked Questions
Is compliance with NZS 3404 legally required on New Zealand construction projects?
NZS 3404 is not legislation, but it is the standard cited within Verification Method B1/VM1 as a recognised means of complying with Clause B1 Structure of the New Zealand Building Code. A designer could pursue an alternative method under the Building Act, but in practice building consent authorities expect structural steelwork to be designed and documented against NZS 3404, and departing from it means demonstrating an equivalent level of safety some other way.
Does NZS 3404 apply to existing steel structures, or only to new buildings?
It applies to both. Part 1’s scope explicitly extends to the modification of existing steel structures, which matters for seismic strengthening, building alterations, additions, and change-of-use projects. Engineers assessing existing steelwork, and the detailers documenting any strengthening work, need to work to the same standard as they would for a new structure.
How does NZS 3404 deal with seismic design?
NZS 3404 is used together with NZS 1170.5, the New Zealand-specific earthquake actions standard, and supports capacity design principles that are standard practice across New Zealand structural engineering. In simple terms, connections and members are proportioned so the structure has predictable, ductile behaviour in a major earthquake rather than a sudden, brittle failure.
Has the revised NZS 3404 been published yet?
Not yet. As of 2026, the revised Parts 1 and 2 and the proposed new Part 3 on durability are both still at public consultation stage. Until Standards New Zealand formally publishes the revised standard and it is adopted into Building Code compliance documents, NZS 3404:1997 Parts 1 and 2 remain the current applicable edition.
Keeping NZS 3404 in View From Design Through to Erection
NZS 3404 sits at the centre of how structural steelwork is designed and consented in New Zealand, but it only delivers a safe, compliant structure when it is carried through consistently: from the design actions calculated under NZS 1170, through member and connection design, into shop drawings and coordinated models, and finally into fabrication and erection under AS/NZS 5131. With a substantial revision of the standard now working through public consultation, it is also a standard worth watching rather than treating as fixed.
For project teams, the practical takeaway is straightforward. Get the standards framework right early, keep compliance documentation current, and make sure the design intent behind every connection survives the journey from calculation to site.
If your project involves structural steelwork that needs to be documented accurately against NZS 3404 and the standards it works alongside, Citotech’s steel detailing team can help turn structural design into fabrication-ready shop drawings and coordinated BIM models. Get in touch to talk through your project’s documentation needs.
