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Do You Know Your Earthquake Classifications?

Posted by Robert Lacy on December 4, 2018

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When the Big One hits, what kind of damage can you expect? While it’s up to fate as to how intense or severe the quake will be — or when it will happen — the fact is set in stone. Earthquakes can and do happen here.


Seattle City Heights and Earthquake Classifications


In fact, Washington state is second only to California when it comes to earthquake risk, and this is reflected in our earthquake classifications.



Quakes Volcanoes and Your Risk in the Ring of Fire

The Effects of Soil Type on Earthquake Damage

Soil Liquefaction, Earthquakes and Underwriting


Earthquake classifications assign a numerical value to a building based on construction features affecting its ability to withstand an earthquake. Unlike building codes, earthquake classifications are based on potential property loss, not life safety. From a property insurance perspective, they predict how specific building materials should perform in terms of loss.

 When evaluating a risk for earthquake coverage, there are many factors to consider, including distance to fault, soil type, liquefaction and of course, construction materials. Here’s a quick guide to the construction component, along with some common exceptions and miscategorizations. 


Earthquake Classifications Quick Reference Guide

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.


Exceptions and common mis-categorizations

  • Load-bearing 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.


Related: PropertyEDGE Hazards video tutorial


Of course, construction materials are just one part of the equation. Where the structure is built can have a huge effect on its potential for earthquake damage, a topic we dive into more closely in our Soil Liquefaction, Earthquakes and Underwriting and Life in the Ring of Fire blog posts.

In the meantime, you can use our PropertyEDGE tool to dive into your specific earthquake risks, or visit Washington’s Department of Natural Resources Earthquakes and Faults page to learn more about risks from earthquakes, volcanoes, tsunamis, and other natural disasters.


“Editor’s Note: This post was originally published in June 5, 2013 and has been updated for freshness, accuracy and comprehensiveness.

Topics: Insurance underwriting, Building Construction, GIS Mapping, Inspections, insurance, Hazards