On a fabrication floor, nobody cuts steel from an architect’s drawing. The saw operator works from a member mark, a cutting length, a bevel angle and a hole pattern, and if any one of those numbers is wrong, the error travels straight to site as a beam that will not fit. That translation from design intent into buildable instruction happens in the shop drawing.
So, what are shop drawings? They are the detailed, fabrication-level documents that tell a fabricator, precaster or installer exactly how to manufacture and assemble each component of a structure. For engineers, builders, project managers and estimators, they are also one of the most programme-critical deliverables on a project. This guide explains what shop drawings contain, how they are reviewed and approved, where they sit in the construction programme, and where projects most commonly lose time and money on them.
Key Takeaways
- Shop drawings translate design intent into fabrication instructions, showing every dimension, hole, weld, cast-in item and mark needed to manufacture a component.
- They are produced by or on behalf of the fabricator, subcontractor or supplier, then reviewed by the designer for conformance with the design, not redesigned by them.
- A complete structural steel set typically includes general arrangement and erection drawings, assembly drawings, single-part drawings, bolt and material lists, and often CNC data.
- Shop drawing production and approval sits on the critical path, so late design decisions and slow review turnaround directly delay fabrication and delivery.
- Accurate detailing reduces site rework, crane standing time and variation claims far more cheaply than fixing the same problem in the air.
- Detailing must reflect relevant New Zealand Standards and the design engineer’s requirements, including material grades, weld details and fabrication tolerances.
Shop Drawings Versus Design Drawings: Two Different Jobs
Design drawings, sometimes called consent or construction issue drawings, communicate design intent. They establish the structural system, member sizes, loads, grid lines, performance requirements and the design philosophy for connections. They are prepared by the consulting engineer or architect and are the basis for building consent.
Shop drawings do something narrower and deeper. They take that intent and resolve it into a set of manufacturing instructions for one component or assembly at a time. Where a design drawing may note “310UC118 column, moment connection to beam”, the shop drawing defines the plate thicknesses, weld type and size, bolt grade and length, hole diameters, edge distances, cut lengths, camber, coating and the unique mark that identifies that piece in the yard.
Who Prepares and Who Reviews
Shop drawings are the responsibility of the party doing the manufacturing, which is usually the fabricator, precaster or services subcontractor. In practice they are often prepared by a specialist detailing consultancy engaged by that party, or occasionally directly by the main contractor to de-risk their programme.
The design engineer or architect then reviews them for general conformance with the design intent. That review is a check, not an approval of the fabricator’s dimensions, quantities or means of construction. Understanding that distinction matters commercially, because it defines who carries the risk when a piece does not fit.
What a Shop Drawing Set Actually Contains
The content varies by trade, but the underlying principle is constant: every piece that will be manufactured needs enough information to be made without interpretation.
Structural Steel
A structural steel package is usually organised into layers of information rather than a single drawing type:
- General arrangement and erection drawings: plans and elevations showing where each marked piece sits, erection sequence notes, bolt sizes at each joint and site weld locations.
- Assembly drawings: each fabricated assembly shown with overall dimensions, attached plates and cleats, welds, holes, and its assembly mark.
- Single-part drawings: individual plates, gussets, stiffeners and cut members with cutting dimensions, bevels and hole patterns.
- Bills of material and bolt lists: quantities, grades, lengths, surface treatment and mass, used for procurement and for lifting calculations.
- CNC and fabrication data: machine-readable files extracted from the model for beam lines, plasma and drilling equipment.
Weld symbols, hole tolerances, member marks and grade callouts are all shown on the assembly and single-part sheets. This level of resolution is why structural steel detailing is treated as a specialist discipline rather than a drafting task, since the detailer is constantly interrogating connection geometry, access for bolting, and fabrication practicality.
Precast Concrete
Precast shop drawings, often called production or element drawings, define each panel or unit as a manufactured product. They typically show panel elevations and sections, reinforcement layout and bar schedules, cast-in items such as ferrules and connection plates, lifting and propping inserts, cover requirements, surface finish, demoulding and lifting weights, and the panel mark used through casting, storage, transport and erection.
Because a precast element cannot be modified easily once cast, the coordination burden sits almost entirely in the detailing stage. Penetrations for services, cast-in fixings for façade or interior elements, and connection hardware all need to be resolved before the mould is set.
Mechanical, Electrical and Plumbing
For services, shop drawings take the form of coordinated installation and fabrication documents: ductwork layouts and spool sheets, pipework spools with cut lengths and fitting schedules, cable containment routes, plant room arrangements, hanger and support details, and builder’s work penetrations. Their main function is to prove that every service can be installed in the available space, at the required gradients, with maintenance access retained.
Where Shop Drawings Sit in the Construction Programme
Shop drawings are almost always on the critical path, because material cannot be ordered or cut until they are settled. A typical sequence runs:
- Design drawings and specifications issued to the fabricator or subcontractor.
- Detailer builds a 3D model or drawing set from that information and raises requests for information on gaps and conflicts.
- Shop drawings submitted for review by the design consultant and main contractor.
- Comments returned with a review status, then incorporated and resubmitted where required.
- Drawings released for fabrication, material procured, production commences.
- Erection drawings issued to site, with revisions tracked against as-fabricated status.
The two variables that most often blow out this sequence are unresolved design information and review turnaround. A detailer waiting on a confirmed slab level, a façade fixing location or a connection design cannot progress the affected zone, and every day of that wait is a day the fabrication shop is not loaded.
Managing the Review Cycle
Most projects use review status codes such as approved, approved with comments, or revise and resubmit. Keeping cycles short is a project management discipline as much as a technical one. Practical measures that help include agreeing a submission programme by zone rather than a single bulk issue, nominating a single reviewer per package, setting a defined turnaround period in the subcontract, and consolidating comments before returning them so the detailer is not chasing conflicting instructions.
The Commercial Case: Why Detailing Quality Shows Up on Site
The cost of an error scales with how late it is found. A mislocated bolt hole picked up in the model costs minutes. The same hole found on the fabrication floor costs a repair and a QA sign-off. Found at 12 metres with a crane hooked on, it costs crane standing time, a delayed follow-on trade, a site instruction and often a variation claim.
Well-executed detailing also reduces the volume of RFIs during construction, because the questions have already been asked and answered before fabrication. That is one reason contractors increasingly bring detailers into the design coordination conversation early rather than treating shop drawing preparation as a downstream production task that starts only once the design is fully frozen.
The Role of 3D Modelling and Clash Detection
Most steel and precast detailing is now model-based, with drawings extracted from a 3D model rather than drawn in isolation. The practical benefits are consistency between views, automatic material take-offs, direct output to CNC machinery, and the ability to federate the fabrication model with architectural and services models to find clashes before anything is manufactured.
Clash detection is particularly valuable at interfaces: steel bracing against duct runs, precast panel penetrations against pipe routes, hangers against post-tensioned slabs. These are exactly the conflicts that are cheapest to solve in a model and most expensive to solve on site.
Standards, Tolerances and Compliance in New Zealand
Shop drawings must reflect the design engineer’s specification and the relevant New Zealand Standards. For steel structures, NZS 3404 is the principal reference for design and fabrication requirements, covering matters such as material grades, welding requirements, bolting categories and fabrication tolerances. Current editions and scope can be confirmed through Standards New Zealand.
Documentation also supports compliance more broadly. Fabrication and installation records, welding procedures, material certificates and inspection sign-offs are all tied back to the marks and details shown on the shop drawings, which is what allows work to be verified against the consented design and the New Zealand Building Code. Where a specification calls for a particular fabricator certification or inspection regime, the drawings need to carry the information those inspections rely on.
A common practical failure is silence on tolerances and fit-up. If a drawing does not state whether a hole is standard or oversize, whether a bolt is snug-tightened or fully tensioned, or how a site weld is to be prepared, the decision defaults to whoever is holding the tool. Good detailing removes that ambiguity.
Common Shop Drawing Problems and How to Avoid Them
Across most projects, the same issues recur:
- Detailing started on incomplete design information. Producing drawings from a partial design guarantees rework. It is usually faster to resolve the open items first, even if that feels like lost time.
- Unclear connection design responsibility. If the subcontract does not state who designs connections, the detailer, the engineer and the fabricator can each assume it belongs to someone else.
- Late services coordination. Penetrations and cast-in fixings identified after casting or fabrication become site drilling, patching and structural review.
- Poor revision control. Fabricating from a superseded revision is one of the more expensive administrative errors on a project. Every sheet needs a clear revision status and issue purpose.
- Underestimating detailing duration at tender. Detailing hours are frequently priced optimistically, then compressed, which pushes errors downstream.
Frequently Asked Questions
Are shop drawings the same as as-built drawings?
No. Shop drawings are produced before manufacture to instruct fabrication and installation. As-built drawings are updated after construction to record what was actually built, including approved changes made during the works. On some projects, marked-up shop drawings form part of the as-built record, but the two serve different purposes at different stages.
Who pays for shop drawings, and who is liable if they contain an error?
Shop drawings are normally part of the fabricator’s or subcontractor’s scope and priced within their package, unless the contract states otherwise. Responsibility for accuracy generally remains with the party that prepared and submitted them. A designer’s review for conformance with design intent does not usually transfer liability for dimensional errors, so it is worth checking exactly how your contract words this.
Do shop drawings need to be signed off by a chartered engineer in New Zealand?
There is no blanket requirement covering all shop drawings, but project specifications and consent conditions frequently require designer review, and any element of design carried out by the detailer or fabricator (commonly connection design) must be undertaken or verified by a suitably qualified engineer. The specification and consent documents for the individual project govern the process.
Can shop drawings be produced from PDFs or 2D drawings only?
Yes, and this is still common on smaller or refurbishment projects. It generally takes longer and carries more risk, because the detailer must reconstruct geometry, verify inconsistencies between views and raise more RFIs. Where a coordinated 3D design model is available, detailing is usually faster and clash issues are found earlier.
How long does shop drawing production take?
It depends on tonnage or element count, connection complexity, how much design information is settled and the review turnaround agreed. Rather than relying on a rule of thumb, the reliable approach is to programme detailing by zone or release, tie each release to a fabrication start date, and build the review period into the programme explicitly.
Treating Shop Drawings as a Project Control, Not Paperwork
Shop drawings are where a design becomes a physical, buildable set of components. They carry the dimensions the saw cuts to, the marks the crane crew calls out, the cast-in items the façade relies on and the clearances the services need. Handled well, they compress site duration, reduce RFIs and keep variations off the table. Handled as an administrative formality, they become the source of the very problems everyone is trying to price out.
The controllable factors are consistent across steel, precast and services work: release complete design information, define connection design responsibility clearly, coordinate in 3D before manufacture, hold review turnaround to an agreed period, and maintain disciplined revision control from first issue to release for fabrication.
If you are planning a project and want your fabrication documentation to hold up under review, on the shop floor and on site, Citotech’s team works across structural steel and precast concrete detailing, BIM modelling and CAD drafting for New Zealand construction projects. Send through your drawings, model or specification and we can talk about scope, programme and how the package is best staged, so get in touch with your project details when you are ready to map it out.
