There is no fixed line; it is decided case by case on the contract, but the party preparing detailed shop or working drawings takes design decisions and, absent a clear contrary indication, is liable for them, the most useful test being that shop drawings implement the design rather than create it

There is no fixed line. On most standard forms the architect or engineer designs the works, with provision for some design by the contractor, and many engineering forms make the contractor responsible for the detailed design; where the boundary falls between the designer's work and the contractor's shop or working drawings must be decided case by case on the contract. In one case installation drawings were found not to be design drawings, but the courts have made clear that installation drawings can embody design: in detailing the work the party preparing the drawings takes design decisions, and absent a clear contrary indication it will be liable for them. The most useful test is purpose: design drawings say what is to be built and how the system works, while shop or working drawings convert that information into a format for manufacture and fixing, but the line blurs wherever the contractor's drawings fill gaps the design left.