We updated our previous earthquake classifications for buildings
As of April 1, 2025, we have updated our earthquake classifications for buildings to align with the latest structural engineering standards and risk assessment methodologies. These updates reflect changes in how different construction types respond to seismic activity and improve accuracy in risk evaluations.
This article provides an overview of the new classifications and how they correspond to the previous system.
What changed?
- New classification names: We have simplified and restructured the categories to be more intuitive.
- Refined definitions: Classifications now more precisely reflect modern construction materials and techniques.
- Alignment with industry standards: These changes ensure better consistency with seismic risk modeling.
View comparison chart between old and current earthquake classifications
Wood Frame (A1)
Includes wood frame or frame stucco buildings.
Excludes structures with concrete-supported floors or unit masonry/concrete walls.
Previously classified as: 1C, 1D
All-Metal Buildings (B1)
Includes all-metal buildings, including those with wood or cement-asbestos roofing and/or siding.
Previously classified as: 2A, 2B
Steel Frame (C1)
Buildings with a complete steel frame carrying all loads.
- Floors and roofs: Any material.
- Exterior walls: Any non-loadbearing materials.
Previously classified as: 3A, 3B, 3C
Reinforced Concrete and Structural Steel (D1, D2, D3)
D1
Structural system consists of one or a combination of the following:
- Poured-in-place reinforced concrete frame.
- Poured-in-place reinforced concrete interior and/or exterior walls.
- Partial structural steel frame with reinforced concrete.
Floors and roofs: Poured-in-place reinforced concrete, except for buildings over three stories, which may use other materials.
Previously classified as: 4A, 4B
D2
Reinforced concrete frame or combined reinforced concrete and structural steel frame.
- Floors and roofs: Any material.
- Exterior and interior walls: Any non-loadbearing materials.
Previously classified as: 4D, 5AA (not tilt-up)
D3
Structural system includes:
- Partial or complete load-carrying system of precast concrete.
- Reinforced concrete lift-slab floors and/or roofs.
- Otherwise qualifies for D1 or D2.
Concrete, Brick, or Block (E2, E3)
E2
Buildings with load-bearing walls of:
- Unreinforced brick.
- Other unreinforced solid unit masonry.
- Hollow tile or other hollow unit masonry construction.
Floors and roofs: Any material.
Previously classified as: 5B, 5C
E3
- Buildings having load-bearing walls of adobe.
- Also includes buildings not covered by any other classification.
- Previously classified as: 5C
Comparison chart: Previous to current classification