Unreinforced Masonry Buildings
Un-reinforced masonry buildings (UMB’s) are buildings with exterior walls made of brick, stone, concrete, or similar materials and slab floors. They are considered “un-reinforced” because their masonry walls do not have reinforcement –typically steel- anchoring them to the floor. They are designed to support gravity pressure (vertical) as opposed to side to side pressure.
The Department of Building Inspection considers UMB’s to be at higher risk of collapse during an earthquake than reinforced masonry buildings and has identified over 2000 units in San Francisco they consider to be UMB’s.
Owners of UMB’s with 5 or more units are required to retrofit their buildings to minimum requirements prescribed by San Francisco law. Retrofitting deadlines are determined by the buildings location and occupancy. The minimum standard of retrofitting is referred to as “Bolts Plus”. This involves bolting the walls to the floors and installing wall supports.
For more specific information about UMB”s contact the Seismic Safety Division of the DBI at 415-558-6083.