Basis of design is descriptive rather than restrictive — the design intent, layout, and coordination with adjacent trades are all built around that one product's actual dimensions and performance, so a true substitution has to prove equivalence across all of that, not just meet a generic performance number. That's a heavier lift than it sounds: the burden usually falls on the contractor or the proposing manufacturer to demonstrate fit, not on the engineer to disprove it. Basis-of-design language shows up most often in mechanical, electrical, and plumbing spec sections, where equipment dimensions and connection points genuinely constrain the rest of the design around them. This distinction matters enormously to manufacturers and reps, because getting specified as the basis of design is a much stronger commercial position than being named as one of several acceptable manufacturers — most contractors simply buy the named product rather than build a substitution case. Seeing which live projects name a product as basis of design, versus listing it among several acceptable options, is exactly the kind of spec-level detail Nonlinear surfaces when it reads a project's documents.
Knowledge Base
What is a basis-of-design product?
A basis-of-design product is the specific manufacturer's product the engineer used to develop the design — its dimensions, performance data, and connections are built into the drawings — even when the spec technically allows an "or equal" substitution.
