IBC 2024 Seismic Design Categories: Map and ASCE 7-22 Methods

Under the 2024 IBC, first assign the structure’s Risk Category and establish the site condition. Then determine its Seismic Design Category (SDC) by one of the two methods permitted by §1613.2:

1. use the applicable IBC Figure 1613.2 map for the structure’s Risk Category and qualifying default site conditions; or
2. determine the category under ASCE 7-22.

If the authority having jurisdiction or geotechnical data identifies Site Class DE, E, or F, the IBC map method is not available; §1613.2 requires the ASCE 7 method. The result is a category from A through F, but that letter is an input to later structural and nonstructural checks—not a stand-alone statement that a proposed building complies.

What changed in the 2024 IBC workflow?

The 2024 IBC references ASCE 7-22 and adds seven SDC figures as a permitted determination method. It also reflects the ASCE 7-22 site-class system, which adds intermediate Classes BC, CD, and DE.

That matters because an older IBC/ASCE 7-16 workflow cannot simply be relabeled “2024.” In particular, the previous version of this page reproduced the older Fa/Fv coefficient method and older SDS/SD1 category tables as if they were the complete current procedure. ASCE 7-22 instead obtains the applicable ground-motion parameters from the USGS Seismic Design Geodatabase; the ASCE Hazard Tool provides the corresponding ASCE 7-22 parameter report.

Do not carry a result, table, site coefficient, or section number from another edition into a 2024 design without checking the current adopted standard.

The two permitted determination paths

The IBC method is not a generic earthquake-zone map. The seven figures are organized by geography and show categories for Risk Categories I–III and IV under default site conditions. Select the applicable figure and risk-category side of the map; do not infer a category from a city name or a statewide generalization.

The ASCE 7-22 path is also more than looking up one acceleration. Chapter 11 coordinates site class, risk category, ground-motion parameters, design response spectra, and SDC assignment. The structural engineer must retain the inputs and the tool/report version used for the project.

Step 1: Confirm the adopted code and referenced standard

Verify the jurisdiction’s adopted building code, effective date, local amendments, and referenced ASCE 7 edition. This guide addresses the unamended 2024 IBC with ASCE 7-22. A jurisdiction using the 2021 IBC, ASCE 7-16, or a locally modified seismic map requires a different edition-specific workflow.

Also check the scope and exceptions in IBC §1613.1. The section applies ASCE 7 Chapters 11, 12, 13, 15, 17, and 18 as applicable, but it contains stated exceptions. “Every structure is assigned A through F” is therefore too broad without first checking the section’s scope.

Step 2: Assign Risk Category

Assign Risk Category under IBC Table 1604.5 from the building or structure’s use and the consequences of failure. For a building containing portions that would fall into different categories, apply §1604.5.1 rather than automatically selecting a category from the primary occupancy label.

Risk Category is not the same as occupancy classification. Occupancy classification describes use under Chapter 3; Risk Category is the structural consequence classification used by Chapter 16 and ASCE 7. Record the exact Table 1604.5 basis because the IBC map and ASCE 7 results depend on it.

Step 3: Establish the site condition

ASCE 7-22 Chapter 20 uses these site classes:

The actual classification must follow the complete Chapter 20 procedure and measured soil properties; the descriptors are not substitutes for the classification criteria.

When the soil properties are not known in enough detail, ASCE 7-22 §11.4.2.1 uses Site Class D subject to §11.4.4, but the default ground-motion response is based on the most critical response at each period across Site Classes C, CD, and D. The default is therefore not the old shortcut “select Site Class D and apply the old D-row coefficients.”

If the AHJ or geotechnical data identifies DE, E, or F conditions, use the ASCE 7 path. A geotechnical report may also trigger site-specific evaluation or other requirements elsewhere in ASCE 7.

Step 4: Obtain the current ground-motion record

For the ASCE path, use the ASCE Hazard Tool with:

• the project latitude and longitude;
• ASCE 7-22 as the standard version;
• the assigned Risk Category; and
• the determined site class or the tool’s ASCE 7-22 default selection.

ASCE’s published API documentation identifies the 7-22 selections as Default, A, B, BC, C, CD, D, DE, and E. Site Class F is not a simple drop-down result because it requires the site-response procedure. Retain the generated report, its coordinates, source version, site-class selection, and retrieval date with the project calculation record.

Do not substitute a generic USGS hazard-map screenshot for the project record. ASCE 7-22 uses the USGS Seismic Design Geodatabase through the standard’s parameter workflow, and a location or input change can change the output.

Step 5: Determine and record the SDC

For the IBC map path, read the applicable Figure 1613.2 category from the project location and Risk Category. For the ASCE path, determine SDC under ASCE 7-22 §11.6 using the current ground-motion parameters and rules.

Do not reproduce the old two-table SDS/SD1 lookup as a universal 2024 answer. Do not apply the old S1 ≥ 0.75g override language from a previous edition without confirming the current ASCE 7-22 provision. The current standard and the retained output record control.

If a map boundary, site condition, location, or risk-category assignment is uncertain, document the uncertainty and obtain a determination from the structural engineer or authority having jurisdiction rather than choosing the lower category.

What does the SDC control?

The category helps select the later seismic-design requirements, but it does not by itself determine one mandatory structural system. Depending on the project, the following can be affected:

• seismic force-resisting-system permissions and limits;
• analysis procedures, configuration, height, and irregularity requirements;
• material-specific proportioning and detailing;
• diaphragms, collectors, anchorage, and load paths;
• nonstructural component and architectural-system requirements;
• geotechnical investigation and site-hazard requirements;
• special inspection, testing, and structural-observation provisions; and
• documentation and quality-assurance requirements.

Apply the exact ASCE 7 chapter, material standard, IBC provision, occupancy, risk category, system, height, and exception. Statements such as “all SDC D buildings require a special moment frame” or “response-history analysis is usually required in SDC F” are not reliable system-selection rules.

What belongs on the construction documents?

IBC §1603.1.5 requires the earthquake design data to be shown even where earthquake loads do not govern the lateral force-resisting-system design. Coordinate the current section’s list, including:

• Risk Category and seismic importance factor;
• mapped and design spectral response parameters;
• site class and Seismic Design Category;
• basic seismic force-resisting system or systems;
• design base shear, seismic response coefficient, and response modification coefficient; and
• analysis procedure used.

The notes must agree with the structural calculations, geotechnical assumptions, ASCE Hazard Tool report, system selection, details, and schedules. A category label copied from a prior project is not a design record.

A practical verification record

Before issuing the structural basis of design or permit set, record:

1. jurisdiction, adopted IBC edition, amendments, and referenced ASCE 7 edition;
2. project coordinates and the coordinate source;
3. Risk Category and its IBC Table 1604.5 basis;
4. site class, geotechnical basis, and any AHJ determination;
5. selected IBC-map or ASCE 7 path and why it is permitted;
6. source figure or downloaded ASCE Hazard Tool report;
7. resulting SDC and the person responsible for the structural determination; and
8. downstream system, nonstructural, geotechnical, inspection, and drawing-note checks.

Frequently asked questions

Can I use the IBC map without a geotechnical report?

The IBC map method is permitted for the §1613.2 default-site condition unless the AHJ or geotechnical data identifies DE, E, or F soils. That permission does not remove geotechnical-investigation or site-specific requirements elsewhere in the adopted code and ASCE 7.

Is Site Class D still the 2024 default?

ASCE 7-22 uses Site Class D when properties are insufficiently known, subject to §11.4.4, but the default ground-motion response considers the most critical response across Classes C, CD, and D. Do not use the older Site Class D coefficient workflow as the 2024 procedure.

Does SDC D require one specific lateral system?

No. System permissions and limitations depend on ASCE 7, the material standard, Risk Category, height, irregularities, and other project conditions. The SDC is one input to that evaluation.

Can an architect determine the final category from this page?

This page explains the code sequence. The registered design professional responsible for the structural design must make and document the project-specific determination using the adopted code, ASCE 7, geotechnical information, and AHJ requirements.

Scope and limitations

This guide covers the unamended 2024 IBC/ASCE 7-22 determination sequence. It does not perform a structural design, classify a specific site’s soil, replace a geotechnical investigation, reproduce the copyrighted standard’s complete tables, or resolve local amendments and AHJ determinations.

Primary sources

• IBC 2024 §1613.2: Determination of Seismic Design Category
• ICC: 2024 IBC Significant Structural Changes
• ASCE: ASCE/SEI 7-22
• ASCE Hazard Tool
• ASCE Hazard Tool API documentation
• ASCE/SEI 7-22 Chapter 20: Site Classification Procedure

Correction history

• 2026-08-31 — Revision 1: Replaced the ASCE 7-16-style coefficient and SDC tables with the 2024 IBC/ASCE 7-22 two-path workflow; added BC, CD, and DE site classes and the current default-site condition; corrected the construction- document section to §1603.1.5 (Earthquake design data; §1603.1.6 is geotechnical information); removed unsupported city, cost, plan-review, system-restriction, and response-history claims; and added edition, source-record, and downstream-verification requirements.