The city's seismic ordinance classifies the various building code occupancies into five "relative hazard" levels. To go back to the warehouse vs. day care center example, a day care would be classified at a higher hazard level than a warehouse. When you change the use of a building in a way that the seismic ordinance considers an occupancy change to a higher relative hazard, you could be required to upgrade the entire building. Whether or not a seismic upgrade is required usually depends on the floor area of the change in relation to the building as a whole. In some cases, a building may need to be upgraded seismically because the change of use is seen as dramatically increasing the number of occupants.