TL;DR (generated, confidence: high)

Portland City Code Chapter 24.85 establishes seismic design requirements for existing buildings undergoing occupancy changes or alterations, with specified acceleration parameters and exemptions for pre-1974 buildings through 2029.

Key points:

Until Jan 1, 2029, most buildings built before 1974 do not require seismic evaluation reports for additions or alterations, though URM buildings and occupancy changes remain subject to requirements (Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗)
Chapter 24.85 first adopted in 1994, underwent major revision in October 2004 which became the governing code for seismic design of existing buildings (Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗)
Section 24.85.040 triggers seismic upgrades when occupancy or use change results in increase of 150 or more occupants (Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗)
Applicants can request exemption for up to 10% increase in occupant load (from October 1, 2004 baseline) via building code appeal to waive seismic upgrade triggers (Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗)
BSE-1E (20% probability exceedance in 50 years) spectral acceleration parameters Sxs and Sx1 have 75% floor relative to BSE-1N values (Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗)
BSE-2E (5% probability exceedance in 50 years) spectral acceleration parameters Sxs and Sx1 must be at least 75% of BSE-2N but not exceed BSE-2N values (Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗)

Entities: code_section: Chapter 24.85 | code_subsection: Section 24.85.040 · Section 24.85.065 | seismic_hazard_level: BSE-1E · BSE-2E · BSE-1N · BSE-2N | parameter: Sxs · Sx1 | building_type: Unreinforced Masonry Buildings

Chapter 24.85 - Seismic Design Standards for Existing Buildings

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Source: Chapter 24.85 - Seismic Design Standards for Existing Buildings ↗ Last modified: Sun, 19 Apr 2026 20:06:45 GMT

Please note: Until Jan. 1, 2029, most buildings built before 1974 do not require seismic evaluation reports when proposing additions or alterations. Seismic upgrade requirements may still apply to unreinforced masonry buildings or other projects with changes in occupancy. Please visit this page ↗ to find out more information or schedule a free 15-minute appointment ↗ to ask structural engineering questions about a commercial project.

First adopted in 1994, Portland City Code Chapter 24.85 "Seismic Design Standards for Existing Buildings" contains requirements for upgrade to the lateral systems of existing buildings when the buildings are undergoing change of use or occupancy or are being altered. In addition, for Unreinforced Masonry Buildings (URM's) undergoing alterations or repair, Section 24.85.065 has triggers associated with the cost of repair or alteration which, if exceeded, would require mandatory seismic strengthening.

In 2004, Chapter 24.85 underwent a major revision. This revised version, adopted in October 2004, serves as the governing code for seismic design for existing buildings.

Per requirements in Section 24.85.040, Change of Occupancy or Use, when a change of occupancy or use results in an increase in occupant load or 150 or more occupants, a seismic upgrade may be triggered. Is there an avenue to allow for a larger increase in occupant load for large buildings with high occupancy without triggering a seismic upgrade?

Based on pastprovisions in Oregon Structural Specialty Code and IEBC as amended by Building Codes Division and past precedent, PP&D may consider a request to allow an increase in occupant load of up to 10% of the occupant load as of October 1, 2004, if the 10% increase in occupant load would result in an increase in occupant load that is larger than 149 occupants. If an applicant wishes to submit for consideration to allow up to 10% increase in occupant load for the purposes of waiving seismic upgrade triggers of section 24.85.040, a building code appeal would need to be submitted. Get information on how to file an appeal ↗.

What are the limitations on the use of Sxs and Sx1 acceleration parameters associated with BSE-1E and BSE -2E ground motions in Chapter 24.85?

BSE-1E is the Basic Safety Earthquake-1 for use with the Basic Performance Objective for Existing Buildings, taken as a seismic hazard with a 20 percent probability of exceedance in 50 years except that the design spectral response acceleration parameters Sxs and Sx1 for BSE-1E seismic hazard level shall not be taken as less than 75 percent of the respective design spectra response acceleration parameters obtained from BSE-1N seismic hazard level.

BSE-2E is the Basic Safety Earthquake-2 for use with the Basic Performance Objective for Existing Buildings, taken as a seismic hazard with a 5 percent probability of exceedance in 50 years except that the design spectral response acceleration parameters of Sxs and Sx1 for BSE-2E seismic hazard level shall not be taken as less than 75 percent of the respective design spectra response acceleration parameters obtained from BSE- 2N Seismic hazard level and may not be greater than BSE-2N at a site.