Downers Grove's Seismic Design Category, explained

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Downers Grove in Seismic Design Category B: Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. Nationally, Downers Grove ranks above 43% of the 4,875 cities in this dataset for seismic hazard - the 43th percentile.

Downers Grove by the numbers

The raw figures: peak ground acceleration 0.067g, short-period spectral response 0.131g, 1-second spectral response 0.066g. Among 330 Illinois cities in this dataset, Downers Grove ranks 117 for seismic hazard, the 65th percentile within the state. About 50,552 people live in Downers Grove, Illinois.

Bracing and bolting: the actual cost

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.

Insuring against this, not just retrofitting

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 Downers Grove address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Downers Grove'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.