What is a shop drawing? It is a fabrication and erection drawing produced by the contractor, developed in detail from the approved design documents, detailed enough for a workshop to cut material from it and a crew to erect from it.
The commonest confusion sits right there: a shop drawing is not the approved construction design. The two differ in who produces them, when, and what legal weight they carry — and mixing them up is behind most arguments about who is responsible when a drawing turns out wrong.
This article separates the two, says who prepares shop drawings, and sets out the submittal process with its four possible outcomes. It then covers how shop drawings differ across steel, concrete, services and finishes, and why drawings come back unapproved.
Shop drawing versus the approved design
Vietnam's Construction Law sets out formal design stages, and construction drawing design is one of them: a design step, produced by the designer. "Shop drawing" appears in no decree or statute — it is a trade term, borrowed from English, for the further detailing the contractor does from documents that have already been approved.
| Construction drawing design | Shop drawing | |
|---|---|---|
| Produced by | The design consultant | The contractor, a subcontractor or a fabricator |
| Based on | The design brief, the preceding design stage, codes and standards | The approved construction drawing design and the project specification |
| Level of detail | Enough to build and to price | Enough for a workshop to fabricate and a crew to erect |
| Approved by | The employer approves it | The designer and supervision consultant review; the employer accepts |
| Binding because | Statute and the design contract | The construction contract and the specification, not a statute of its own |
Answering the question what is a shop drawing properly means including that last row. How binding shop drawings are on a given job is set by the contract, not by a decree. Decree 207/2026/ND-CP on quality management and construction execution sets the inspection framework but never names shop drawings. Where the specification says "no steel member is cut before its shop drawing is approved", that clause binds. On a house with no specification, nobody is penalised. So the first job of a detailer is to read the specification, not to open the software.
There is a second consequence, and it matters when something goes wrong: an approved shop drawing does not transfer design responsibility to whoever approved it. The contractor remains answerable for the dimensions, quantities and buildability of the drawings it produced. That is why approval stamps usually carry a disclaimer.
Who prepares shop drawings
Depending on the package and the contract:
- The main contractor's technical department — for ordinary structural and finishing work.
- Specialist subcontractors — services, aluminium and glazing, ceilings and partitions, lifts. Each details its own scope and submits through the main contractor.
- The fabricator — pre-engineered steel, precast concrete. Here the drawing feeds the cutting line directly, so one wrong number is a wrong batch of steel.
Job adverts call this role shop drawing engineer or detailer; on the steel side it is exactly the work the Institute's Tekla Structures course trains for. The general requirements: read the design drawings of all three disciplines, know the detailing software, and understand how things are made — knowing whether what you have drawn can actually be fabricated.
The submittal loop and its four outcomes
This is where most of a detailer's time goes, and the part that online articles skate over.
Completed drawings go out as a submittal, with a reference number, a date, the package and a drawing list. The reviewer returns one of four results:
| Result | What it means |
|---|---|
| Approved | Build to this drawing |
| Approved as noted | Buildable once the comments are incorporated; no formal resubmission, but many projects require a corrected copy for the record |
| Revise and resubmit | Not yet buildable; correct it and submit again as a new revision |
| Rejected | Fundamentally wrong; start over |
Each resubmission carries a new revision number. A common convention uses letters (Rev A, B, C) for submissions before approval and numbers (Rev 0, 1, 2) for the approved-for-construction issue and later changes — but the convention written into the contract is the one that applies. The drawing in use on site must be the latest approved revision, and superseded copies have to be withdrawn. On many sites the commonest paperwork accident is not a wrong drawing but building from a superseded one.
Review periods are normally written into the contract, commonly 7 to 14 working days per round. For a package that needs two or three rounds, that is a month — so the submittal schedule has to sit inside the construction programme. What is the critical path? names this group exactly: the invisible activities that usually sit on the critical path.
How shop drawings differ by discipline
Four disciplines, four toolsets, four sets of expectations.
| Discipline | What the drawings contain | Usual tools |
|---|---|---|
| Structural steel | Fabrication drawings per member, erection drawings, material lists, piece marks | Tekla Structures, Advance Steel |
| Reinforced concrete | Reinforcement detailing per member, bar schedules, joint and anchorage details | Revit, AutoCAD, rebar software |
| Building services | Coordinated layouts, levels and routes, supports, penetration drawings issued to the structural team | Revit MEP, AutoCAD |
| Finishes | Tile setting-out, ceiling and partition details, glazing, joinery and fixed furniture | AutoCAD, SketchUp, Revit |
Two points are worth drawing out. First, services must be detailed earliest even though they are installed last, because penetration drawings have to reach the structural team before the concrete is poured. Late, and you are coring holes afterwards — expensive, and it weakens the structure.
Second, steel is the least forgiving, because the drawing feeds the cutting machine and nothing can be corrected once the steel is cut. The steel trade's own sequence — approval drawing, shop drawing, erection drawing and material list — is covered in steel shop drawings: from a Tekla model to fabrication drawings.
Why shop drawings come back
From the submittals students bring to class, these repeat most:
- It does not match the approved design. A dimension, level or material differs with no written approval for the change.
- Disciplines are not coordinated. A duct through a beam, a support landing in a wall, a ceiling that no longer has headroom once the services are threaded through. Most of it is catchable by running a clash check on the model before submitting.
- It does not follow the specification. The spec says grade 8.8 bolts, the drawing says 4.6; the spec says a full penetration weld, the drawing shows a fillet.
- There is not enough information to fabricate. Missing dimensions, missing material grades, missing connection details, missing erection tolerances.
- Numbering and revisions are a mess. No consistent reference, unclear revision, a transmittal list that does not match the drawings attached.
What the five have in common: none of them is bad draughtsmanship. Every one is a reading failure — the design, the specification, or the neighbouring discipline. Reading a full set is the precondition for detailing it, which is what the construction drawing reading course covers.
Detailing from a model
The old way was to redraw from scratch in AutoCAD against the design drawings. The way large contractors work now is to build a model and issue drawings from it: change the model and every plan, section and schedule updates with it.
The real gain is not drafting speed but consistency. Drawing by hand in AutoCAD, one change means remembering to correct five other sheets; forget one and the set contradicts itself. Issued from a model, that cannot happen, and the material list comes from the same model as the drawings.
The trade-off is that the model has to be right from the start, and whoever builds it has to know the drawing conventions of their trade. How BIM differs from Revit is about the gap between operating the software and working to the process.
Frequently asked questions
Is a shop drawing legally required?
No statute requires one specifically. It becomes required when the contract or the project specification asks for it — and on any job with structural steel, complex services or a glazing package, it almost always does.
If an approved shop drawing turns out wrong, who is liable?
The contractor that produced it remains answerable for its content. Acceptance by the consultant does not relieve that, which is what the disclaimer on approval stamps says. Liability shifts only where the error came from the approved design itself.
How is a shop drawing different from an as-built drawing?
A shop drawing is produced before construction and describes what will be built. An as-built is produced afterwards and records what was actually built. See what an as-built file must contain.
What software should a detailer learn?
By discipline: Tekla for structural steel, Revit MEP for services, Revit or AutoCAD for concrete and finishes. But software is the necessary part, not the sufficient one — reading the design set and understanding fabrication is what makes the difference.
How long does approval usually take?
Commonly 7 to 14 working days per round, as written in the contract. Plan for more than one round on anything complex, and put the submittal dates in the programme.