Seismic design starts with the site. Mapped acceleration values (Ss and S1) combine with the site class — a soil classification — to give the design spectral accelerations (SDS, SD1). Those set the Seismic Design Category, A through F, and IBC 1613 adopts ASCE 7 for the method.
The SDC is the pivot point: higher categories require stricter detailing and limit which lateral systems you can use. Get the site class or SDC wrong and the whole seismic system may be under- or over-designed.
A common mistake is a design-criteria sheet missing the site class, the seismic parameters, or the resulting SDC — the exact values a reviewer needs to verify the category. Reviewers confirm the SDC determination and check that the structural system chosen is permitted for that category.
This guide describes the model code for general understanding and is not a substitute for the adopted code and amendments enforced by your local authority having jurisdiction. Verify all figures against your jurisdiction's codes of record.