The following items address frequently asked questions concerning structural design requirements within the jurisdiction of the City of Portland.
General Design Requirements
The following requirements are applicable to both commercial and residential projects located within the jurisdiction of the City of Portland.
- Soils: Foundation and retaining wall design parameters may be based upon the default soil properties of the building code or as justified by submission of a Geotechnical Report.
- 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. Lateral pressures for walls supporting sloping backfill or surcharge loads must be determined by a Geotechnical Report.
- Design of basement and retaining walls shall include lateral soil loads due to earthquake motions.
- Soil frost depth is 18-inches.
- The minimum design roof snow load is 20 psf + 5 psf rain on snow surcharge where applicable per the Oregon Structural Specialty Code.
- Ground snow load used for determining drift requirements is based on Snow Load Analysis for Oregon as published by the Structural Engineer Association of Oregon. Ground snow loads at a specific site can be determined at the following link: http://snowload.seao.org/lookup.html.