A basis of design records the main assumptions, standards, criteria, and decisions that guide a project’s design.
Definition
A basis of design explains how the project team translated goals and requirements into technical choices. Depending on the discipline, contract, and project phase, it may document codes, owner criteria, design assumptions, selected systems, alternatives considered, and reasons for key decisions. Firms use it to support design coordination, quality reviews, owner discussions, and future understanding of the work. The level of detail and format vary, so the document should fit the agreed deliverables and the decisions that need to be understood. A basis of design is not the design itself, a guarantee of performance beyond the contract, or a substitute for calculations, plans, specifications, or required approvals. It may need revision when project criteria or assumptions change. The International Code Council offers model-code resources that can inform the standards identified when applicable.
How owners use it
- Record major assumptions and technical decisions so reviewers can follow the reasoning behind the design.
- Use the document during coordination to surface differences between owner requirements, discipline assumptions, and adopted provisions.
- Update the basis when a material criteria change affects a design choice.
- A team records the selected drainage approach, governing criteria, and key assumptions in the basis of design for owner review.
