Hilton Head Island's Seismic Design Category, explained

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Hilton Head Island in Seismic Design Category D: High seismic hazard - this is the category most of coastal California, the Pacific Northwest, and other active fault regions fall into. Code mandates significant seismic detailing and restricts irregular structural configurations. This is the category the Brace + Bolt scope (cripple-wall bracing, foundation bolting) is built for. Rank it against the rest of the country and Hilton Head Island sits at the 83th percentile for seismic hazard among 4,875 US cities.

Where Hilton Head Island sits in South Carolina

The raw figures: peak ground acceleration 0.245g, short-period spectral response 0.439g, 1-second spectral response 0.147g. Among 66 South Carolina cities in this dataset, Hilton Head Island ranks 15 for seismic hazard, the 78th percentile within the state. About 38,158 people live in Hilton Head Island, South Carolina.

Bracing and bolting: the actual cost

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for South Carolina. 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 Hilton Head Island address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Hilton Head Island'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.