Rockford's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, Rockford is Category B. Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. Rank it against the rest of the country and Rockford sits at the 34th percentile for seismic hazard among 4,875 US cities.

Rockford by the numbers

The raw figures: peak ground acceleration 0.056g, short-period spectral response 0.11g, 1-second spectral response 0.059g. Among 330 Illinois cities in this dataset, Rockford ranks 269 for seismic hazard, the 19th percentile within the state. About 147,486 people live in Rockford, Illinois.

What a retrofit costs in Rockford

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for Illinois. A typical retrofit still runs $5,000-$10,000 nationally, about $7,000 for a common single-family job.

Earthquake insurance for a Rockford home

Outside California, earthquake coverage is typically sold as an endorsement added to a standard homeowners policy, not a separate product - worth asking about directly when getting a home-insurance quote for a Rockford address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Rockford's numbers. The guide to what a Seismic Design Category actually means covers why a category is never a substitute for an engineer's assessment of one specific house.