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Structural Design Requirements for One and Two-Family Residential Structures

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Get information about structural and engineering requirements for one and two-family residential projects in the City of Portland.
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The current state building code governing Prescriptive One- and Two- Family Residential construction is the 2017 Oregon Residential Specialty Code (ORSC), which is based upon the 2015 International Residential Code (IRC) as amended by the State of Oregon; and for the Engineered One- and Two- Family Residential construction the current state building code is the 2019 Oregon Structural Specialty Code (OSSC).

Your project needs to meet all the requirements of the building code.  The structural requirements for residential projects may be designed using either the prescriptive method or needs to be engineered by a registered design professional, or a combination of the two design methods.    

Prescriptive Design 

In the prescriptive path,  the ORSC (Oregon Residential Specialty Code) provides conservative method of construction to ensure the building will resist gravity, wind and earthquake loads.   

Prescriptive Gravity Design Values 

  • The minimum design roof snow load is 20 psf + 5 psf rain on snow surcharge where applicable per the Oregon Structural Specialty Code.  

  • For live loads, refer to ORSC Table R301.5 

Note: Calculations are required for any beam over 10’ long or supporting a point load. 

Prescriptive Lateral Design Values 

Prescriptive lateral design maybe accomplished by using braced wall panels, continuous sheathing and tie-down anchors, per Section R602.10 of ORSC. Note that plans and calculations are not needed to show that a structure will resist wind and earthquake loads for a “minor” addition – Lateral Bracing for Minor Dormer Additions. 

The following are design values that may be used for prescriptive residential design: 

Wind: Applicable design wind pressure is 18 psf (ASD). 
Seismic: Applicable Seismic Design Category is D1.  

Engineered Design 

If your design does not meet the prescriptive path, you will need a licensed design professional, certified in Oregon. They will need to prepare engineering calculations and drawings to show the structure can resist vertical and lateral loads in accordance with the Oregon Structural Specialty Code (OSSC). For structural design requirements, refer to Structural Design Requirements for Commercial Structures.  

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