Glossary
What is basis-of-design (and why does it drift)?
Basis-of-design is the document that records the criteria and assumptions an engineering design is built on — loads, redundancy, code references, setpoints — so everything downstream rests on a stated foundation.
Basis-of-design (BOD) is the engineering document that captures the criteria a design must meet and the assumptions behind it: design loads, redundancy requirements, applicable codes and standards, key setpoints, and the reasoning that ties them to the project's requirements. Everything that follows in the design depends on it.
It tends to drift because it's written by different people, under deadline, often by copying the nearest previous project. Without a single standard that's easy to follow, small differences accumulate — and across several projects for the same client, the inconsistency becomes visible.
Keeping it consistent is a documentation problem, not a design problem: the goal is to capture and check the criteria the same way every time, while the engineering judgment about what the criteria should be stays entirely with the engineer.
See also
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