Indiana Building Design Criteria by County

Beyond frost depth and snow load, Indiana's substituted Table R301.2(1) fixes the rest of the residential design criteria county by county. Wind speed is uniform: 115 mph in all 92 counties, with wind exposure determined on a site-specific basis under Section R301.2.1.4. Weathering is classified Severe and termite risk Moderate to Heavy throughout, and ice shield underlayment is required in every county. The value that varies most is the seismic design category: forty-seven counties are Category A, thirty-one are B, and fourteen are C, with the higher categories concentrated in the southwest of the state near the New Madrid seismic zone. Footnote b allows the category to be assigned either from the table or under Section R301.2.2.1.1. The table also carries an air freezing index and a mean annual temperature for each county, both of which matter chiefly when designing a frost-protected shallow foundation.

These are design inputs enforced through plan review and inspection rather than offences in their own right. Drawings specifying assemblies below the stated criteria, a roof without the required ice shield underlayment, or a structure designed for a lower seismic category than its county carries, are corrected at review or flagged at inspection before work proceeds.