The Uniform Commercial Code defines “usage of trade” custom as:
…any practice or method of dealing having such regularity of observance in a place, vocation, or trade as to justify an expectation that it will be observed with respect to the transaction in question. (U.C.C. Sec. 1-205(2))
A 2 × 4 is not 2″ × 4″, but 1½″ × 3½″. An 8″ CMU is 75⁄8″. Customs always seem unusual at first, but through familiarity eventually make sense. If the designer referred to “a 2 × 4,” you could rely on a dimension of 1½″ × 3½″. If, however, that designer referred to “2″ × 4″ blocking,” be careful. Does the “Ambiguities” rule apply?
To establish trade custom as the definition of meaning, it must be shown that the custom is followed with absolute regularity. It is not sufficient that it is “usually” done in a certain manner; it must be a usage that is observed in virtually all cases in the area in which the contract is being performed.
Finally, trade custom cannot be relied on as an excuse if the requirement is clear and subject to one reasonable interpretation. When the roofing contractor says, “I never cut reglets,” read the specification. He may be cutting reglets on this job.
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