These guidelines are general in nature and represent requirements for engineered systems for solar installations on typical residential roof types consistent with the typical housing stock within the City of Portland. Requirements for existing structures with complex roof framing systems may fall outside these guidelines and require additional documentation and/or analysis. You may also submit questions about this page.
- Drawings may not contain color; Line quality and contrast must be easy to read and dark enough to scan.
- Dimensions and Notes must be printed to match 12-point font minimum.
- All plans, building sections, and elevations must be drawn to scale; the scale used must be clearly shown.
- Drawings that depict structural information shall be stamped/signed by an engineer registered in Oregon.
- Get more information on minimum submittal requirements.
Residential Engineered System Solar specific drawing guidelines
In accordance with section 1603 of the Oregon Structural Specialty Code (OSSC), construction documents should include the following structural design information:
- Design Snow Load: In accordance with section 1608.2.4 the minimum design sloped snow load, ps, used for design shall not be less than 20 psf times the importance factor, Is, plus the rain-on-snow surcharge where applicable.
- Basic Design Wind Speed: In accordance with OSSC section 1603.1.4 Basic wind speed V(mph), 1609.3.1 and wind exposure. In the City of Portland, the Basic Wind Speed shall not be less than 98 mph (Reference OSSC Table 1609.3).
- Dead load: In accordance with OSSC section 1603.1.8.1 The dead load of rooftop-mounted photovoltaic panel systems, including rack support systems, shall be indicated on the construction documents.
The structural design criteria noted above should be included on the first page or the cover sheet of the drawings. This page shall be stamped by a Registered Design Professional, registered in Oregon.
As required by OSSC 107.2.1, construction documents need to clearly show the location, nature and extent of the work proposed and show in detail that it will conform to the provisions of this code and relevant laws .
The roof framing plan should include the following:
- When roof is framed using manufactured trusses provide a simple roof plan showing the spacing of manufactured trusses (not to exceed 24” o.c.).
- When roof is framed using stick framing, show existing structural framing members including rafter size and spacing ridge board or ridge beam, hip or valley framing, and support posts/bearing walls. Posts, bearing or pony walls below the roof which support the roof framing shall be shown dashed.
- Clearly show the spacing and locations of racking attachment points to the existing roof structure.
Provide a full building section at each location where a new PV array is located (not required when roof is framed using pre-engineered roof trusses):
- Section should specify all existing structural framing members (bearing walls, ceiling joists, roof rafters, collar ties, pony walls, ridge beam or ridge board, diagonal braces, and/or any other pertinent structural framing members).
- Clearly identify any new strengthening members (sistered members, added braces or collar ties, etc.) in the section and indicate the connections to the existing framing. Any strengthening member added shall show or describe the size and spacing of attachments to the existing framing members.
- Clearly identify which elements are new and which are existing.
Identify the size and spacing of new or existing members if not already indicated on plan drawing.
- Provide solar rack attachment detail showing the attachment to the existing framing. Clearly identify PV panel, racking system, attachment hardware, and required fasteners.
Residential Engineered System Solar structural analysis guidelines
For building alterations such as addition of solar panels to an existing roof, the OSSC requires that any existing gravity load-carrying structural element for which an alteration causes an increase in design gravity load of more than 5 percent shall be replaced or altered as needed to carry the gravity loads required by the Building Code for new structures (OSSC 3405.1 [IEBC 503.3] and OSSC 3408.6 [IEBC 806.2]).
Addition of roof mounted PV arrays is an alteration to the load path and load application to the existing roof members. The dead load of the solar panels and the snow and wind loads on the panels are now imparted to the existing roof rafters at discrete points at the racking standoffs as compared to the existing uniform distribution of loads; this change in load path oftentimes exceeds the 5 percent increase when compared to the existing uniformly distributed loads. Calculations therefore must consider point loads due to snow, dead and wind loads at the point of attachment of the standoffs in addition to other loads in the analysis.
Analysis of the existing structure shall include the following:
- Design shall consider the 20 psf minimum low-slope roof or sloped roof snow load as required by OSSC 1608.2.3 and 1608.2.4.
- Where a ridge is framed by a ridge board that is not directly supported by a vertical reaction, the rafters and ceiling joists create a “frame” and must be analyzed as such. The connection of the rafters to the ceiling joists (heel connection) is critical for load transfer and must be determined to be sufficient or strengthened.
- All roof framing members that are affected by the PV installation must be checked. If the existing framing consists of dormers, hips, or valleys, these elements must be evaluated for the modified load path; for this condition, it is not sufficient to check only the roof rafters.
- Where long-span ceiling joists transmit axial load, and are likely spliced over an existing bearing wall, the splice connection shall be verified or strengthened to meet demand.
- Analysis shall determine the adequacy of the existing framing and connections, and provide strengthening as required to address any deficiencies (sistered members, added braces, added collar ties, strengthened connections, etc.).
Analysis of racking attachment to existing structure:
- Design of racking attachment to the existing structure shall be provided considering all governing load cases. Attachments shall be designed to determine fastener size, spacing, and embedment into existing framing.
Residential Engineered System Solar response to structural plan review comments
- To clarify how plan review comments have been specifically addressed, please provide written responses to each checksheet comment and identify where in the calculations or revised drawings the comment has been addressed.