Soft Story

The term “soft-story” refers to one level of a building that is significantly more flexible or weak in lateral load resistance than the stories above it and the floors or the foundation below it (70% or greater reduction from one floor to the next according to the modern, International Building Code (IBC) definition). This condition can occur in any of the conventional construction types and is typically associated with large openings in the walls or an exceptionally tall story height in comparison to the adjacent stories. These soft stories can present a very serious risk in the event of an earthquake, both in human safety and financial liability.
The common sources of soft story vulnerability include:


Ground floor tuck-under parking beneath wood-framed residential apartment buildings.
Tall first floor story heights, typical in older mid-rise and high-rise commercial office buildings where the first floor is generally twice the height of a normal floor above.
Retail buildings with the store front constructed mostly of glass.
Multi-use buildings in urban environments (e.g. San Francisco Bay Area and the Seattle Metropolitan Area) with commercial retail tenants on the ground floor with large glass store fronts and apartment residences above.