Shop drawings

The design team issues drawings that show what is required. The trade that has to make it then produces shop drawings that show how: every member size, connection, weld, fixing, setout dimension and finish. A steel fabricator's shop drawings, for example, include individual piece marks for every beam and column so the workshop can cut and drill them and the erectors know where each one goes.

The typical cycle is:

• Prepare. The subcontractor drafts shop drawings from the IFC drawings and specification.

• Submit. They go to the head contractor, who checks coordination with other trades and forwards them to the designer or superintendent, usually as a submittal with a transmittal.

• Review. The reviewer returns them marked, for example, reviewed no comment, reviewed with comments, or revise and resubmit.

• Fabricate. Fabrication only starts once the drawings come back in an acceptable status.

For a deeper look, read Shop Drawings and Submittals: The Approval Queue That Delays the Programme.

Almost any trade that fabricates off site will produce shop drawings. The most common are structural steel, precast concrete, post-tensioning and reinforcement, facade and curtain wall, windows and glazing, joinery and cabinetry, balustrades, mechanical ductwork, fire sprinklers, hydraulic services and lifts.

The specification usually lists which trades must submit shop drawings, the review period the designer has, and how many review cycles are allowed before the contractor wears the cost of further reviews.

On larger projects, trades such as steel, precast and services often model their work in 3D and produce shop drawings from the model. That makes clash checking against the architectural and structural models much easier, but the reviewed 2D drawings or approved model still need to be controlled like any other project document.

IFC, or issued for construction, drawings come from the designers and show the design intent. Shop drawings come from the trade and show how that intent will be fabricated and installed. As-built drawings, often called work as executed drawings in Australia, are prepared at the end to record what was actually built.

Review of shop drawings does not normally transfer design responsibility to the designer. Most contracts say the contractor remains responsible for errors in its shop drawings even after they have been reviewed, so read the review clause and stamp wording carefully.

• Fabricating before review. It saves a week until the steel arrives and does not fit.

• No coordination check. Shop drawings from different trades often clash. The head contractor needs to check them against each other, not just forward them.

• Hiding design changes. If a shop drawing departs from the design, call it out clearly. A change slipped through review can still be rejected on site.

• Poor revision control. Fabricators working from an old revision is a classic cause of rework. Track every revision and supersede the old ones.

• Late submissions. Long review periods and multiple cycles can put fabrication on the critical path.