Design Phases: SD, DD, and CD
The three stages a building's design passes through on its way to being biddable: Schematic Design (SD), which sets the basic layout and look, Design Development (DD), which works out real systems and materials, and Construction Documents (CD), the fully detailed drawings a contractor can actually build and price from.
Why it matters
An estimate's accuracy depends heavily on which of these three stages the design has actually reached. A number pulled from schematic design is a rough placeholder, while a number pulled from completed construction documents reflects real, buildable detail, and knowing which stage a set of drawings represents is essential to understanding how much an estimate can be trusted.
On a real project
An estimator pricing a project at the schematic design stage flags the number as preliminary, since walls, systems, and finishes are still subject to change. By the time the same project reaches construction documents, the estimate tightens considerably because every detail that affects cost has finally been drawn.
Who this matters most to
An Estimator prices a project differently, and with different confidence, depending on which design phase the drawings represent.
Where this goes wrong
A client is given a single number early in schematic design and treats it as a final budget, without being told how much the design will still change before construction documents are complete. By the time CD drawings are finished, the real cost has grown well past that early number, and the client feels misled even though the estimator never claimed that number was final.