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Do You Know Your Earthquake Classifications?

June 5, 2013

Earthquake classifications assign a numerical value to a building based on construction features that affect its ability to withstand an earthquake.  Unlike building codes, these classifications are based on potential property loss, not life safety. Therefore, from an insurance perspective, it can give you a more accurate idea of how specific building materials are expected to perform in terms of loss.

Below is a quick reference guide to earthquake classifications.


Wood frame

1C –

Habitational: Dwellings, 100% apartment and condominium

buildings, not exceeding 2 stories. No area limit.

Non-habitational: 3 stories or less and 3,000 square feet or less in

ground floor area.

1D –

Area and height limits not qualifying for 1C 


Metal frame

2A –

1 story and 20,000 square feet or less ground floor area.

2B –

Area and height limits not qualifying for 2A. 


Steel frame

3A –

Floors and roofs: Poured-in-place reinforced concrete or concrete

fill on metal deck. Open web steel joists excluded.

Exterior Walls: Non-load-bearing and poured-in-place reinforced

concrete or reinforced unit masonry.

*Column-free areas greater than 2,500 square feet do not qualify.

3B –

Floor and roof: Poured-in-place reinforced concrete, or metal, or

any combination, except building over 3 stories may have roofs of

any material.

Exterior Walls: Any non-load bearing material.

3C –

Floor and roof: Any material.
Exterior Walls: Any non-load-bearing material. 


Reinforced concrete frame

4A –

Exterior Walls: Poured-in-place reinforced concrete or reinforced

unit masonry.

a. Poured-in-place reinforced concrete frame;
b. Poured-in-place reinforced bearing walls;
c. Partial structural steel frame with a. and/or b.
*Column-free areas greater than 2,500 square feet does not qualify

4B –

Exterior Walls: Any non-load-bearing material.
Structural System as in 4A.

4C –

d. Precast load carrying system and/or
e. Reinforced concrete lift-floor slabs and/or roof; and
f. Otherwise qualifying for 4A or 4B.

4D –

Structural System as above but with:
Exterior Walls: Any non-load-bearing material.
Floors and roofs: Any material. 



 5A – This EQ class is not used in Washington State

5AA –

Floors and roofs: wood or metal
Exterior Walls: Load-bearing:
a. Poured-in-place reinforced concrete; and/or
b. Precast reinforced concrete; and/or
c. Reinforced brick masonry; and/or
d. Reinforced hollow concrete block.

5B –

Floors and roofs: Any material.
Exterior Walls: Load-bearing of unreinforced brick or other

unreinforced solid masonry units, excluding adobe.

5C –

Floors and roofs: Any material.
Walls: Load-bearing of hollow tile or other hollow unit masonry

construction and/or adobe.

Also included are buildings not covered by any other class.


Here are some exceptions and common mis-categorizations to look out for:

  • Tilt-up concrete construction is 5AA, not 4C.
  • All-metal buildings with combustible sheathing and/or insulation are 2A or 2B, not 1C or 1D.
  • Interior finish does not affect earthquake classification.
  • All-metal buildings should be Class 2, not Class 3, regardless of size or type of steel supports.
  • Steel Frame Buildings with non-load-bearing reinforced concrete panel walls are classified 3B or 3C, not 5AA.
  • Buildings with metal stud walls and wood truss roofs are classed as 5C. Structures which are classified as wood frame but have concrete supported floors and/or some walls of unit masonry or concrete are excluded.
  • Basement walls are generally excluded unless the basement is partially buried and considered a story.
  • Brick and stone veneers do not affect a building’s EQ classification.
One Comment leave one →
  1. May 13, 2015 1:27 pm

    Earthquake insurance is so expensive, but in the long run is well worth having if you live in an earthquake prone region. Earthquakes seem to be occurring more frequently are much larger, creating so much devastation mostly from structures falling on top of people. It’s important to know how structurally safe your home is and be able to prepare accordingly.

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