The document must connect the brief to the selected system
The Basis of Design should explain what the client requires, which inputs are verified, what remains assumed, which options were tested and why the selected strategy meets the project criteria. A catalogue of equipment types does not provide that chain of reasoning.
Separate facts, assumptions and decisions
Facts have an identifiable source and date. Assumptions are temporary inputs with an owner and closure date. Decisions identify the approving party, the alternatives considered and the downstream consequence. This separation prevents an early convenience assumption becoming an invisible contractual requirement.
State responsibility where the design changes hands
Specialist equipment, controls, smoke-control systems, suppression, utilities and contractor design frequently cross appointment boundaries. The Basis of Design should identify who sets the performance criteria, who completes the design, who coordinates it and who accepts the final evidence.
Record departures and conflicts
Local law, client standards and international guidance can impose different criteria. The governing hierarchy and any departure must be explicit, with the technical justification, approval route and residual risk recorded. Quietly selecting the most convenient clause is not design governance.
State what the document cannot promise
The report should not guarantee authority approval, construction cost, energy performance or a third party’s installation. It records the design basis at a stated stage. Outcomes still depend on complete information, coordinated development, procurement, installation, controls, commissioning and operation.
Keep it alive through change control
The Basis of Design must carry a status, revision, author and checker. When architecture, occupancy, utilities, procurement or equipment changes, the affected criteria, calculations and deliverables must be reviewed.
Acceptance criterion
The Basis of Design is effective when another competent engineer can identify the inputs, reproduce the logic, understand responsibility, locate unresolved risks and verify whether the issued design satisfies the approved criteria.