Why Shop Drawings Need Their Own Gantt Tasks

Why do shop drawing approvals cause so many schedule overruns?

When a contractor orders structural steel, precast concrete elements, custom aluminium windows, or a large electrical panel board, the fabricator cannot begin production until approved shop drawings are in hand. Most Thai SME contractors know this in theory but leave the review window out of the Gantt entirely, treating it as something that happens in the background while other work proceeds. In practice, a first-round shop drawing submission takes the designer ten to twenty-one calendar days to review. When the drawings come back with comments — which they almost always do — the contractor revises and resubmits, and a second review takes a further seven to fourteen days. By the time approval is received, the fabrication lead time has not even started, and the installation milestone is already four to six weeks behind before a single piece of steel has been cut.

What is a shop drawing and which trades typically need one?

A shop drawing is a detailed, contractor-prepared drawing showing exactly how a component will be fabricated and installed — dimensions, connections, finishes, and tolerances — as distinct from the design drawings the architect or engineer produced. For Thai SME residential and light commercial projects, trades that commonly require shop drawings or equivalent approval documents include structural steel connections, precast beam and column elements, reinforcement placement drawings for foundations and slabs, custom aluminium facade and window systems, large electrical panel boards and motor control centres, air-conditioning duct layouts, and specialty stone or tile cladding where patterns must be set before cutting. Most projects above 50 million baht carry at least two or three of these, and missing any one of them from the schedule creates a fabrication delay that tracks forward to the handover date.

How do you add shop drawing tasks to SiteBoard's Gantt planning view?

In SiteBoard's Gantt planning view, create a separate task for each stage of the shop drawing cycle: one task for the supplier's drawing preparation, one for the formal submission, one for the designer's review window, and one for fabrication. The supplier preparation task starts when the contractor receives the design drawings. The review task starts at submission and runs for a fixed duration — fourteen to twenty-one calendar days depending on the contract. Fabrication starts only after the review task is complete and approval is confirmed. Setting these as sequential dependencies — preparation, submission, review, fabrication, delivery, installation — builds an honest timeline that reveals the real date on which an order must be placed. Without these tasks in the schedule, the Gantt shows an installation date that is physically impossible, and the overrun only becomes visible when a crew arrives on site to find no material waiting.

What does a typical shop drawing timeline look like for Thai projects?

For a Thai light commercial project involving structural steel trusses or a precast slab system, the shop drawing cycle runs approximately as follows. The contractor receives the final structural drawings, typically in project week four or five. The supplier prepares shop drawings over seven to ten working days. The contractor reviews for obvious errors before formal submission. The designer reviews and returns comments within fifteen calendar days — the industry norm, and some contracts state it explicitly. If comments require revision, a second round of five to ten working days plus a further seven-day review is needed. First-round approval rarely arrives under four weeks from submission; two rounds commonly take six to eight weeks. For a project where structural installation was planned to start in week eight, that milestone is already impossible if shop drawings were not submitted by week two. Planning the cycle from day one changes the start of the project, not just the end.

A real example: aluminium windows held a Bangkok renovation for seven weeks

A contractor in Bangkok renovating a three-storey shophouse with custom aluminium facades priced the job at 3.2 million baht and planned a sixteen-week programme. The structural steelwork and aluminium windows were the longest-lead items, and the Gantt showed aluminium installation starting in week eight. No shop drawing submission or approval task was added to the programme. The aluminium fabricator confirmed it needed approved shop drawings before starting production. The project manager submitted the drawing package in week five — the first point anyone thought to do it. The designer took three weeks to return two pages of comments. Revised drawings went back in week nine. Second approval came in week eleven. Fabrication took four weeks. Windows arrived on site in week fifteen, seven weeks late, and the project finished in week twenty-three, overrunning by seven weeks on a single missing planning step.

How do you track submission and approval status in SiteBoard?

Track shop drawing submission and review status as on-site progress updates attached to the relevant Gantt tasks in SiteBoard. When the drawing package is sent to the designer, update the submission task to 100% complete and add a note with the submission date and document version number. When comments come back, update the review task and note the comment reference. When approval is received, mark the review task 100% complete and log the approval number. This builds a dated record that, if a dispute arises over why fabrication was delayed, shows exactly when submission was made, how long the designer took, and whether resubmission was required. Owners with access to the owner sharing link can see the approval status of each specialist item without calling the project manager for a separate update.

What happens when the designer takes longer than the contract review period?

Many Thai construction contracts, particularly government and institutional jobs, specify a review period of fifteen to twenty-one calendar days and require a written rejection notice if the designer cannot meet that deadline. When the review runs over, the contractor has grounds to record a delay and, if it flows through to an installation milestone, to apply for a time extension. The correct action is to log the submission date as an on-site progress update in SiteBoard, note the contract review deadline in the task description, and send a written reminder — a LINE message serves as a paper trail — to the designer or owner at the deadline. Do not assume that a late review is simply the way things work. Late reviews are a documented cause of project delay, and when the pattern repeats across three or four submittals, the compounded days consume all programme float before a single installation trade has mobilised.

FAQ: Who is responsible for preparing shop drawings — the contractor or supplier?

In a traditional lump-sum contract where the contractor hires a steelwork or precast supplier, the supplier typically prepares the shop drawings as part of their scope and the contractor acts as coordinator and first reviewer before formal submission to the engineer. In a design-and-build contract the contractor may carry a larger portion of the engineering detail. In either case, the contractor owns the submission and its timeline, not the supplier. If the supplier is slow to prepare, the delay flows back to the contractor's programme. Add a supplier preparation task before the submission task in the Gantt — typically seven to ten working days — so the preparation window is visible and can be chased before the formal submission deadline is already at risk.

FAQ: How many shop drawing packages does a typical project carry?

Most Thai SME projects between 30 and 100 million baht carry three to eight separate shop drawing packages, each with its own submission and review cycle. Structural connections, precast elements, aluminium facades, electrical panel boards, and air-conditioning duct layouts each typically run as separate packages reviewed by different designers. The most common mistake is treating them mentally as a single item when they are actually three or four parallel chains, each capable of delaying a different trade. In SiteBoard's Gantt planning view, each package gets its own submission and review task in the relevant trade row, so if the precast review slips by one week it shows immediately as a risk to the precast installation row — not as a surprise on the day the erection crew arrives.

FAQ: What if the project has no formal shop drawing requirement?

Smaller Thai residential projects and straightforward renovations sometimes proceed without formal shop drawing cycles, particularly where the contractor self-performs all trades and structural details are standard. Even so, any fabricated item — a prefabricated staircase, custom metalwork gates, specialty glazing — has a production lead time that begins when an order is confirmed with final dimensions. Treat the dimension confirmation step as the equivalent of a shop drawing approval: it is the moment that separates design from production, and it belongs in the Gantt planning view as a task with its own duration and a dependency on whatever design step must complete before that dimension is locked. Planning the confirmation date is more useful than planning the delivery date when fabrication speed is outside the contractor's control.