On a steel-framed building, the moment a fabricator starts cutting material is the moment design intent becomes irreversible. A holding-down bolt set out 15 mm off centre, a beam cut 10 mm short, or a cleat drilled on the wrong face does not get resolved with a revised note on a drawing. It gets resolved with a truck, a crane, and lost days on the programme.
That gap between engineering design and workshop production is where steel detailing sits. Understanding what is steel detailing, what it produces, and where it fits in the project sequence helps engineers, project managers, builders and fabricators plan realistic lead times and avoid the rework that quietly erodes margin. This guide explains the deliverables, the review process, the standards that apply in New Zealand, and the practical decisions that determine whether a steel package runs smoothly or stalls.
Key Takeaways
- Steel detailing translates structural engineering design into the fabrication and erection information a workshop and site crew can build from, primarily shop drawings, erection drawings, and material lists.
- The detailer models every member, connection, bolt, weld and hole, resolving clashes and dimensional conflicts before material is cut.
- Deliverables typically include general arrangement drawings, assembly and single-part drawings, an advanced bill of materials, and CNC data files for automated cutting and drilling.
- Detailing does not replace engineering design. Connection design remains the responsibility of the design engineer, with detailing documenting and coordinating that intent.
- In New Zealand, steelwork is generally designed and documented in accordance with NZS 3404 and the requirements of the New Zealand Building Code, alongside project-specific fabrication specifications.
- Detailing sits on the critical path. Late or incomplete design information delays approvals, which delays procurement, fabrication and erection.
What Steel Detailing Actually Involves
Steel detailing is the process of producing the detailed drawings, models and data that a fabricator uses to manufacture structural steel members, and that an erection crew uses to assemble them on site. It takes the structural engineer’s design drawings, which communicate member sizes, loads, geometry and design intent, and converts them into precise, buildable instructions.
The distinction matters. A design drawing might specify a 310UB40 beam with a moment connection to a column. A detailer must determine and document the exact beam length after allowing for the connection, the end plate thickness and dimensions, the bolt grade, diameter, quantity and spacing, the weld type and size, the hole positions to the millimetre, the surface treatment, and the mark number that ties that member to a position in the building.
Modern detailing is model-based. The detailer builds a three-dimensional model of the steel frame in specialist software, with every plate, bolt and weld represented as a real object. Drawings and material lists are then extracted from that model, which means the geometry is verified once and reported consistently across every output. Detailers working within a wider coordinated environment also link this model into the project’s federated structural steel detailing and BIM workflow so that steelwork is checked against concrete, services and cladding before release.
Detailing Is Not Structural Design
This is one of the most common points of confusion on New Zealand projects. The detailer does not size members or determine load paths. Where connections are not fully designed on the consultant’s drawings, the detailer works to the engineer’s specified connection schedules or standard details, and any connection design remains with the design engineer or a suitably qualified party engaged for that purpose.
Detailing does, however, expose design gaps quickly. Because the detailer must resolve every physical interface, missing information (bolt grades, undefined splice locations, unclear brace work points, absent baseplate details) becomes visible early. Treating requests for information from the detailer as useful design feedback rather than an interruption usually shortens the overall programme.
What a Steel Detailing Package Contains
The deliverables vary with contract scope and fabricator preference, but a complete package generally includes the following.
General Arrangement and Erection Drawings
These show the assembled frame in plan and elevation, with each member identified by its mark number, along with grid references, levels, bolt requirements at each connection, and any temporary bracing or erection sequencing notes. Site crews work from these, so clarity and consistent marking conventions matter more than density of information.
Assembly and Single-Part Drawings
Assembly drawings show a fabricated item as it leaves the workshop, for example a column with baseplate, stiffeners, cleats and shear studs already attached. Single-part drawings cover individual pieces such as plates, gussets and stiffeners, giving cut sizes, hole positions, bevels and bend lines. These are the workshop’s primary production documents, and they are the reason detailed shop drawings are reviewed so carefully before fabrication is released.
Material Lists and Fabrication Data
An advanced bill of materials lists every member, plate, bolt, nut, washer and stud by quantity, grade, size and length, which drives procurement and nesting. Alongside this, the model exports numerical control data (commonly DSTV files) that drives automated beam lines, drilling machines and plasma or laser cutting equipment. Where the workshop is automated, the accuracy of that data directly determines fabrication accuracy.
Connection and Special Details
Bespoke items usually need dedicated detailing attention: moment end plates, column splices, brace gussets with defined work points, seismic connections, cranked or curved members, transfer beams, and interfaces with precast panels or in-situ concrete. These are the details where dimensional error carries the greatest cost.
Where Detailing Fits in the Project Sequence
Steel detailing is rarely appreciated until it delays something. A typical sequence runs as follows.
- Structural design is issued, with member sizes, connection requirements and specification.
- The fabricator or contractor engages a detailer and agrees standards, marking conventions and drawing formats.
- The detailer builds the 3D model and raises requests for information on gaps or conflicts.
- Drawings are issued for review by the engineer, and often the architect and main contractor.
- Comments are incorporated, drawings are approved for construction, and material is ordered.
- Fabrication proceeds against approved drawings and numerical control data.
- Erection drawings and bolt lists support site assembly, with as-built or revision updates as required.
Two pressure points dominate. The first is the review turnaround: a package sitting with a consultant for three weeks stops procurement, particularly for sections with long lead times. The second is design change after approval. Once plates are cut and holes drilled, a change to a slab level or a column position is expensive, so early coordination with the concrete, cladding and services packages is worth the effort it takes.
Standards and Compliance Considerations in New Zealand
Structural steelwork in New Zealand is generally designed to NZS 3404, the Steel Structures Standard, which is cited in support of compliance with the structural provisions of the New Zealand Building Code. Detailers do not apply the standard as designers, but they must document connections, bolt categories, weld categories, fabrication tolerances and material grades in a manner consistent with it and with the project specification. Current standards can be verified through Standards New Zealand.
Seismic considerations give this particular weight locally. Where members and connections form part of a designated seismic-resisting system, the engineer will specify requirements around member designation, weld category, bolt category and protected zones. Those requirements must be carried faithfully onto the drawings, since a workshop cannot infer them from geometry alone.
Practical documentation items that regularly need confirmation include steel grades and any impact testing requirements, surface treatment and coating systems (including masked areas at welded or bolted interfaces), galvanising provisions such as vent and drain holes, fire protection allowances, and welding procedure and inspection requirements.
What Poor Detailing Costs, and How Good Detailing Prevents It
The cost of detailing errors is asymmetric. A few extra hours resolving a connection in the model is trivial next to remedial work on site. Recurring issues in practice include:
- Holding-down bolt mismatches. Baseplate and bolt setting-out drawings issued late, or not reconciled against the foundation reinforcement, leading to core drilling or chemical anchors.
- Clashes with services. Web penetrations not coordinated with ductwork and pipework routes, resulting in unapproved site cutting through beams.
- Interface errors with concrete. Cast-in plates, cleats or corbels that do not align with the precast or in-situ element they support.
- Fit-up problems. Hole positions or bolt clearances that leave insufficient access for a spanner or impact wrench, discovered only at height.
- Material inefficiency. Poor nesting and inaccurate material lists causing over-ordering, or worse, a shortfall on a long lead item.
Strong detailing practice addresses these through disciplined model checking, clash detection against the architectural and services models, consistent mark numbering, and drawings that show what the workshop and the crew actually need without unnecessary clutter. Clear revision control is equally important, as most disputes about steelwork errors turn out to be disputes about which revision was being built from.
How BIM Has Changed Steel Detailing
Model-based detailing has shifted the work upstream. Instead of discovering conflicts during erection, teams identify them during coordination reviews, when a change costs a modelling adjustment rather than a crane hire. Steel models can be federated with architectural, structural concrete and building services models, allowing penetrations, hangers, brackets and support steel to be resolved before fabrication.
The model also carries data beyond geometry: grades, coatings, weights, mark numbers and assembly relationships. That data supports procurement, delivery scheduling, lifting studies and progress tracking, which is why fabricators increasingly value the model itself as much as the drawings extracted from it.
Detailing quality still depends on the person, not the platform. Software will happily model an unbuildable connection, an inaccessible bolt, or a member that cannot be transported on a New Zealand road. Experience in fabrication and erection practice is what turns a geometrically valid model into a buildable one.
Choosing a Steel Detailer for Your Project
Whether detailing is procured by the fabricator or the main contractor, a few practical checks separate a smooth package from a difficult one.
- Familiarity with New Zealand practice. Local grades, section availability, seismic documentation requirements, transport limits and typical fabricator conventions.
- Software alignment. Compatibility with the fabricator’s machinery and the project’s model exchange formats, so numerical control data and federated models transfer cleanly.
- Internal checking process. Who checks the model and drawings before issue, and how clashes and revisions are tracked.
- Capacity against your programme. Steel packages arrive in waves, and review comments often return in bulk. Realistic resourcing matters more than a headline turnaround figure.
- Communication discipline. Requests for information that are specific, consolidated and raised early rather than in a late flurry.
Citotech works across structural steel detailing, precast concrete detailing, BIM modelling and engineering documentation, which means steel packages can be coordinated against the concrete and services models rather than detailed in isolation.
Frequently Asked Questions
How long does steel detailing take on a typical project?
It depends on tonnage, connection complexity and the completeness of the design information, so any estimate given without reviewing the structural drawings should be treated cautiously. A small industrial portal frame building may be detailed in a matter of weeks, while a multi-storey structure with moment frames and heavy transfer steel is usually staged into zones so fabrication can begin on early releases. Review and approval turnaround is often the larger variable, not the detailing itself.
Who pays for steel detailing, the contractor or the fabricator?
In most New Zealand procurement models, detailing sits within the steel fabrication and erection subcontract, so the fabricator carries it as part of their price. On design-and-build or early contractor involvement arrangements, the main contractor may engage a detailer directly to accelerate coordination. What matters commercially is that the scope, review responsibilities and revision allowances are clearly defined in the contract.
What software is used for steel detailing?
Purpose-built 3D detailing platforms such as Tekla Structures and Advance Steel are common, supported by Revit and Navisworks for coordination, and general CAD tools for supplementary documentation. The important question is not the brand but whether the outputs suit the fabricator’s workshop equipment and the project’s model exchange requirements.
What is the difference between shop drawings and erection drawings?
Shop drawings are workshop documents. They show how to fabricate an individual assembly or part, with cut lengths, hole positions, welds and finishes. Erection drawings are site documents. They show where each marked assembly goes in the structure, along with bolt requirements at each connection and any sequencing or temporary stability notes. Both come from the same model but serve different audiences.
Do small projects need formal steel detailing?
Even a single steel beam supporting a residential alteration needs accurate documentation of length, bearing details, cleats, bolts and coating. The scale of the package changes, not the need for it. Small projects are often where undocumented assumptions cause the most disruption, because there is no coordination process to catch them.
Getting the Steel Package Right Before Fabrication Starts
Steel detailing is the point where design intent becomes measurable, orderable and buildable. It produces the shop drawings, erection drawings, material lists and machine data that a fabricator and erection crew rely on, and it resolves the physical conflicts that drawings alone can conceal. Done properly, it is largely invisible: steel arrives on site, fits, and gets bolted up.
The practical takeaways for anyone planning a steel package are to allow realistic time for detailing and review, to resolve design gaps and interfaces early rather than during fabrication, to keep revision control tight, and to treat the detailer as part of the coordination team rather than a downstream drafting service. That approach protects both the programme and the budget.
If you have a steel package coming up and want a clear view of deliverables, coordination requirements or realistic detailing timeframes, Citotech can help. Send through your structural drawings or project brief and the team can outline a practical scope and programme for the steel detailing work involved, get in touch to start the conversation.
