Sandia study reveals most roofs can support the weight of rooftop solar structures
Sandia National Laboratories released the results of a three-year study on Thursday, concluding that most U.S. rooftops in good condition can support the weight of rooftop solar photovoltaic (PV) installation system loads.
“There is a misperception in the building industry that existing residential rooftops lack the strength to carry the weight load of rooftop solar photovoltaic installations,” Sandia Structural Engineer Steve Dwyer said. “Most existing well-built wooden rooftops can support PV system loads.”
After the Department of Energy initiated its Solar America Cities program, some cities reported that the primary barrier to rooftop solar installations was difficulty in obtaining construction permits. Dwyer said this came as a surprise, but he found that most code officials were unknowledgeable about solar technology and how a solar PV system would impact the integrity of a residential roof structure.
In response, Sandia researchers conducted a three-year study testing the weight-bearing capacity of residential rooftops to better inform permit obtainment regulations. The team did this by constructing a number of roofs in a lab and determining exactly how much weight was required to break the structures.
The study determined that most U.S. rooftops in fair condition could withstand the weight of solar PV system loads because the weight-bearing capacity of each rooftop support beam works together to support the structure. On average, the researchers found a 330 percent excess load-bearing capacity of rafters compared to values estimated by the National Design Standard.
