Los Angeles Soft Story Retrofit Benefits and Costs

Porter, Keith Alan

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Los Angeles Soft Story Retrofit Benefits and Costs Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/reports/bk128c43b

Abstract

California has several seismically dangerous building types, but soft-story woodframe buildings are so numerous and vulnerable that San Francisco, Los Angeles, Oakland, and other cities have taken the unusual step of requiring that they be strengthened to better resist earthquakes 1,2,3,4. Los Angeles’ retrofit ordinance has led to 8,100 soft-story apartment buildings being retrofitted, protecting 117,000 housing units 5. Recent estimates suggest that adding ground-story shearwalls, steel frames, or both to strengthen the buildings costs between $80,000 and $160,000 per building in today’s dollars, or about $11,000 per housing unit 6. That implies that Los Angeles property owners have spent about $1.3 billion to retrofit these buildings. How much benefit will that investment produce, in reduced future earthquake losses?

We answered that question using analyses from Natural Hazard Mitigation Saves 7, the most exhaustive benefit-cost analysis of natural-hazard mitigation ever performed. It included a study of retrofitting soft-story conditions in multifamily woodframe housing. It used FEMA’s estimates of where such buildings exist, how many people live in them, and how many occupy them at various times of day 8. It used the US Geological Survey’s estimates of how frequently and strongly earthquakes shake them 9. And it employed models of probabilistic damage given various levels of shaking 10,11. It calculated costs and benefits on a census-tract level and presented them at the county level. We scaled the Los Angeles County results to account for the 117,000 housing units retrofitted to comply with Resilience by Design. Here is what we found.

Los Angeles’ soft-story retrofits will avoid an estimated 1,500 deaths and 27,000 nonfatal injuries and cases of post-traumatic stress disorder. The retrofits will prevent the partial, temporary, or permanent loss of 65,000 housing units, home to 170,000 people. They will reduce future losses by $41 billion in property damage, life-safety impacts, and other economic consequences. See Table 1 and Table 2. The benefits divided by the costs, called the benefit-cost ratio, is 32 to 1, meaning $32 saved per $1 of up-front cost, a very cost-effective investment. For comparison, President Biden convinced Congress to pass the $1.3 trillion infrastructure bill partly by citing the Mitigation Saves estimate of the 6 to 1 benefit-cost ratio for strengthening public-sector infrastructure.

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