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Component Manufacturing dverti$er
Don’t Forget! You Saw it in the
Adverti$er
March 2020 #12248 Page #41
How Important are Construction Tolerances?
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ack in the days before Autoset C®, Matchpoint®, and Wizard®, truss set-ups and the truss profile were dependent on the truss builder’s ability to accurately jig the truss being built using cross reference information and data. For example, a heel to peak measurement was taken to ensure the truss was square and symmetrical. Multiple measurements were made to adjust for variations with the design dimensions. Back in the day, deviations to the design were less important because normally roofs were a set of single profile trusses. Often, they were a set of commons with matching gable ends. We used to have a short hand for orders, no need for cutting sometimes, because the orders were repetitive and predictable. In those days, as long as the trusses were consistent (consistent error) with the order, it didn’t really matter if the trusses were a little higher than design or a little lower. Today, that is not the case. It’s not uncommon to have a run of trusses that have zero matching profiles. To aid in manufacturing, sometimes the same projects are built on different tables, relying on set-ups to be accurate and within tolerances. We can no longer depend on “consistent error.” What are those tolerances? According to ANSI/TPI 1–2014, the tolerances for finished truss units are listed in Table 3.5-1. When these tolerances are not met, the results in the field are undulations in the roof sheathing, telegraphing to the roof materials and resulting in an unattractive product.
Table from ANSI/TPI 1–2014
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