Structural Design Requirements for Commercial Structures

The current state building code governing commercial and engineered residential construction is the Oregon Structural Specialty Code (OSSC). 

Soils and foundations

Foundation and retaining wall design parameters may be based on the default soil properties of the building code or on a Geotechnical Report submitted to justify them. 

• The default allowable foundation bearing capacity within the City of Portland is 1,500 psf (minimum 12” wide footing).
• Default lateral soil load for the design of basement and retaining walls supporting level backfill shall be 40 psf/ft for laterally unrestrained retaining walls and 60 psf/ft for laterally restrained retaining walls. A Geotechnical Report must determine lateral pressures for walls supporting sloping backfill or surcharge loads.
• Design of basement and retaining walls shall include lateral soil loads due to earthquake motions.
• Soil frost depth is 12 inches. 

Snow

• Determine ground snow loads at a specific site: Use the Oregon Design Criteria Hub.
• Determine design snow loads: Use the procedures from the Minimum Design Loads for Buildings and Other Structures (ASCE 7) as modified by the Oregon Structural Specialty Code.

Wind

Determine design wind pressures: Use the 3-second gust wind speed and the procedures of Minimum Design Loads for Buildings and Other Structures (ASCE 7) and the Oregon Structural Specialty Code.

The wind exposure category is site-dependent and must be determined by the Engineer of Record based on site conditions.

Seismic

All locations within or administered by the City of Portland are classified as Seismic Design Category D under the Oregon Structural Specialty Code (OSSC).

Determine site-specific seismic design parameters: With the ZIP code or latitude and longitude, use the Oregon Design Criteria Hub.

Existing buildings: seismic standards and upgrades

Seismic requirements for existing buildings are governed by Portland City Code Chapter 24.85.

A seismic evaluation or upgrade may be required if an existing building undergoes:

• Change of use or occupancy
• Addition
• Renovation
• Alteration
• Re-roof (for unreinforced masonry buildings)

Seismic cost triggers (updated February 2026)

Chapter 24.85 requires certain seismic cost thresholds to be updated annually based on the construction cost index.

These thresholds are adjusted in the first quarter of each year.

(a) Seismic evaluation trigger – Section 24.85.060

An ASCE 41 seismic evaluation report is required when construction costs exceed the current threshold.

Current threshold: $386,338

Temporary exemption (through Jan. 1, 2029)

Most buildings built before 1974 do not require a seismic evaluation report for additions or alterations until January 1, 2029.

However, seismic upgrades may still be required for:

• Unreinforced masonry (URM) buildings
• Projects involving a change in occupancy

For structural engineering questions about a commercial project, schedule a free 15-minute appointment.

Learn more: Code Alignment Project

(b) Unreinforced Masonry (URM) buildings – Section 24.85.065(B)

URM buildings may require seismic upgrades when repair or alteration costs exceed certain thresholds within a two-year period.