Los Angeles' Soft Story Ordinance
By Stefan Duma
Between 2015 and 2016, the city of Los Angeles has issued Ordinance 183983 and 184081 commonly known as “Mandatory Earthquake Hazard Reduction in Existing Wood-Frame Buildings with Soft, Weak, or Open Front Walls” with the intent to reduce collapse risk of wood-frame buildings with soft story.
In the last decades, the built environment of Los Angeles has known the diffusion of wood multi-family residential units designed with tuck-under parking levels, functional for a car-oriented community but often unsafe from a structural standpoint due to discontinuity of bearing perimeter walls to the foundation. In the city of Los Angeles only, the Department of Building and Safety (LADBS) estimates up to 13,500 of soft story buildings at risk in the unfortunate event of a major earthquake.
In the next paragraphs some guidelines for the interpretation of the Ordinance will be provided.
Does you building fall under the Ordinance for soft-story retrofit?
The Ordinance is applicable to your wood-frame building if all the following criteria are met:
- The building was constructed following codes prior to January 1, 1978;
- The ground floor contains open spaces that cause soft, weak or open-front wall lines;
- There are one or more stories above the ground floor.
˟Residential buildings containing 3 or less dwelling units are exempt from the Ordinance.
What is a soft, weak or open-front wall line?
- An open-front wall line is an exterior wall line without vertical elements of lateral force resisting systems.
- A weak wall line represents a vertical wall discontinuity with ground floor wall strength less than 80% of the strength of the wall above. In simple words, less than 80% of the walls above continue to the ground level.
- A soft wall line exists when the wall stiffness in a level is 70% less than the stiffness of the level immediately above. Evaluating this structural weakness is less immediate and it requires a wall material analysis.
What are the Ordinance time limits?
When a property owner receives an order to comply, the following timelines must be respected:
- 60 days to appeal the notice and prove the building is within the scope of the Ordinance;
- 2 years to submit engineering plans for retrofit or demolition plans if needed;
- 3.5 years to obtain the construction permit;
- 7 years to complete the construction of the seismic retrofit or demolition.
Which are the structural systems most commonly used for retrofitting a soft story?
- Use of plywood shear walls. Shear walls are the easiest and cheapest solution for retrofitting a soft story but it requires the reduction of the ground floor openings, rarely acceptable in parking levels;
- Use of moment frames, steel structural elements that resist lateral loads through flexure, maintaining most of the original openings at ground floor;
- Use of cantilever columns; they require additional design requirements, used in special situations.
˟The Ordinance forbids the use of concrete shear walls, masonry shear walls or braced frames due to higher stiffness values compared to wood frame.
MOBBIL INC, provides full retrofitting services for Soft, Weak or Open-Front buildings, in compliance with the City of Los Angeles Ordinance, with more than 20 soft story retrofit projects in its portfolio. For further information or building evaluation, feel free to contact us.