A code baseline, not a house inspection

ASCE 7's Seismic Design Category tells a builder how much seismic bracing NEW construction needs at a given point - it assumes standard soil and standard occupancy, and says nothing about a specific existing house's foundation type, age, or condition. A Category D city can contain a recently-retrofitted home and an untouched pre-1950 one on the same street, at very different actual risk.

Why cripple-wall and foundation-bolt retrofits target older houses specifically

The retrofit scope this site prices - cripple-wall bracing and foundation bolting - exists because older wood-framed houses on raised foundations were built before these connections were required at all, not because of the city's category. A new house in Los Angeles, CA already meets the code its category demands; an unretrofitted 1920s house in the same city may not, regardless of category.

What actually answers the question for one house

Foundation type, house age, and any prior retrofit work all matter more than the city-wide category for deciding whether a specific house needs work. A category is where to start - it says whether the city is a place this even applies - not where to stop; an actual assessment from a structural engineer or a licensed retrofit contractor is what answers the question for one address.

Where to go next

See the range this plays out across: Caruthersville, MO, Noblesville, IN, Marathon, FL.

Earthquake Retrofit Cost and California's Brace + Bolt Grant, in Full · How QuakeRetrofitCheck Reports Your City's Seismic Data