Architects and engineers are required to produce drawings and specifications as construction documents. The documents are developed throughout the design process - Schematic Design, Design Development, and Construction Documents. But the process for creating drawings and specifications is entirely different.
The dichotomy is: Drawings are additive; Specifications are subtractive (and additive).
Drawings start from nothing. They begin as a concept, sometimes the proverbial napkin sketch, to express an idea. The idea is a simple form or plan illustrating a response to a particular problem or need. It is the macro, 50,000 foot view of a future facility to be built to allow an owner to meet a financial or business objective.
The drawings are refined in an additive, progressive process. Sketches become generic electronic models. Additional owner program and budget detail influences the concept - pushing and pulling, requiring the concept form to adjust in response. Boundaries become rigid and fixed to accurately define each space and establish relationships and adjacencies so the facility will function as the owner requires. Single lines become pairs representing the volume of systems and assemblies. Detail is added, slowly.
Finally, the emphasis shifts from macro to micro to hone the details to permit construction. Generic model elements transform to a design solution. Typical details from the master library are applied and modified to suit. System intersections and terminations are defined. Every material is identified and every dimension is set. The addition is complete.
Specifications begin as a design challenge - a confrontation requiring amicable resolution. Drawings are scoured for information and inferences to learn what will be required to complete construction. Results are documented in a table of contents listing each potential specification section. Comments and questions for the design team about technical considerations are added to begin the data gathering quest.
Specifications are drafted as nearly complete documents from masters using both subtractive and additive processes. Irrelevant information is removed from the master. Detail required to describe unique project conditions is added. Reponses from the design team are incorporated. The specifications are tuned to reflect the drawing progress and final design decisions. Subtraction is complete.
And Never the Twain Shall Meet!
Drawings are drawings and specs are specs, and the two must always meet. (apologies to Rudyard Kipling) The contractor relies on the construction documents meeting when they are issued for construction. Ideally, the level of development would be consistent between the two sets of documents. Practically, it never will be, especially when documents are issued for pricing before they are completed. Specifications will always be at a greater level of development than the drawings until they are issue for construction.
So what's the implication?
Contractors will rely on the documents that appear to be most complete. The specifications will control. Therefore the specifications must accurately reflect the design intent, before the intent is clearly shown by the drawings. The document development dichotomy will require the specifications to define scope to aid the contractor or estimator's understanding because the drawings development does not meet the specifications.
How and where will that expensive, exotic wood veneer used? When the drawings don't show it, the specifications must define it so the pricing will be accurate. Simply specifying the veneer, is not enough.
The specifications summary article can be a great help to all. Specify what products will be used, how they will be used and where they will be used. (see Specifying the Architect's Intent) The technique will be especially helpful for identifying unique conditions that might easily be overlooked.