A roof structure is made stronger by the system elements working together—much stronger than its main load-bearing element, the rafter, is alone. Current engineering analysis methods do not take this composite action into account when evaluating rooftop strength.

A roof structure is made stronger by the system elements working together—much stronger than its main load-bearing element, the rafter, is alone. Current engineering analysis methods do not take this composite action into account when evaluating rooftop strength.

Two Sandia research reports, “Structural Code Considerations of Solar Rooftop Installations” and “Empirically Derived Strength of Residential Roof Structure for Solar Installations,” have been featured recently in a number of solar trade outlets.

Sandia tested numerous rooftop structure configurations at UNM’s structures laboratory.

Sandia tested numerous rooftop structure configurations at UNM’s structures laboratory.

The reports detail rooftop structural analy­sis conducted by Sandia and funded by the US Department of Energy’s SunShot Initia­tive. Test results indicate that the actual load-bearing capacity for residential rooftop structural systems is several times higher than published values. These outcomes provide a new data for consideration in evaluating rooftops for solar PV instal­lations.

The reports were highlighted in newsletters from the Solar Energy Industries Association, Solar America Board for Codes and Standards (SolarABCs), and the Interstate Re­newable Energy Council. The reports were also featured in a June article in Solar Builder magazine, a blog post from DOE’s Office of Renewable Energy and Energy Efficiency, and webinars with the Solar Instructor Training Network and SolarABCs (and will be in an upcoming edition of the International Code Council’s Building Safety Journal).

The reports and related items are available on Sandia’s PV website and results are summarized in a related fact sheet.