Brief
The brief is the written statement of what a project must achieve, covering the client's requirements, priorities, budget, timeframe and site constraints.
A good brief captures more than a room count. It records how the household lives, which spaces matter most, what the budget genuinely is, what must be kept from an existing building, and which requirements are non-negotiable versus nice to have.
Briefs evolve. The version agreed at the start is tested by the site analysis, the planning controls and the first cost check, and it is normal for priorities to be re-ranked once the trade-offs are visible.
The brief is also the measuring stick. When options are being compared at concept stage, the question is not which looks better but which delivers more of the brief within the constraints.