According to InterNACHI's ledger-fastener spacing formula, what is the unit of measurement for joist length?

In the context of InterNACHI's ledger-fastener spacing formula, the unit of measurement for joist length is feet. This is standard practice in construction and home inspection, as feet provide a practical scale for measuring the lengths of structural components like joists. When calculating fastener spacing, using feet allows for easier conversion and application when looking at lengths and spans typical in residential construction.

While inches could also be used in some contexts, the choice of feet aligns with common construction practices and makes it more intuitive for inspectors who deal with larger dimensions. Cubic feet refers to volume measurement, which is not applicable to linear lengths, and centimeters, while a valid unit, are less commonly utilized in U.S. construction practices. Thus, feet becomes the preferred and correct unit in this scenario.