The Detailed Design consists of the drawings and written Specification or Schedule of Work needed for builder to carry out the work; the drawings (or for large projects, a sub-set of them) are also used to obtain Building Regulations approval. For small projects this work is carried out by the Architect; for larger projects a Quantity Surveyor may be appointed to prepare the Specification, Schedules of Work or Bills of Quantities, and they will also handle the invitation of competitive tenders.
The preparation of these drawings - known as Production Drawings, or Working Drawings - and the Specification or Schedule of Work, is one of the most time consuming parts of a project, and therefore one of the more expensive activities. However if the project is of any complexity, it is essential to ensure that the work meets expectations, and fulfills the technical and legal requirements which apply.
Changes to the design at this stage can lead to wasted work and abortive fees; don't start this stage both Architect and the Client have agreed exactly what is intended from the Outline Design.
A Structural Engineer may also need to prepare calculations and drawings for the load-bearing parts of the construction, and a Services Engineer may prepare drawings and / or Specifications for heating, electrical installations, ventilation, air conditioning, lift installations and other mechanical and electrical work.