Technicians installing photovoltaic solar array on a high tilt rack located on a sloped roof. Building located at 2415 Prospect Street in Berkeley, California. Photo taken in September 2010 by Alfred Twu.

This picture is a good example of how not to install solar. The wind load on the North roof is increased by the exposed under side of the panel and in strong winds could easily rip the roof off. A good structural engineer would not sign off on this design nor would any educated building inspector. Understanding both the lift and load forces of a solar array on a roof are important for both the longevity of the system and the building.

A properly installed solar array will last 30 years and reduce the environmental degradation of the roof by sheltering it from the harmful UV rays while reducing the cooling load on the building. A poorly installed system such as this will be buffeted by winds which causes the lag bolts to loosen in the roof trusses, breaking the seal of any caulking designed to protect against water infiltration and eventually allow the wood to rot. This will allow the lag bolts to be pulled out during a medium wind storm and the upper array will flip over onto onto the lower panels on the front or collapse backwards onto the back roof deck. The failure may only be partial in which the rack will twist which could lead to the tempered glass in some of the panels breaking rendering the electrical connections open to moisture and short circuits.

In the event of a heavy wind storm, unless the roof was built with properly fastened hurricane clips at each truss, the entire roof could be lifted and torn off. From the age of this building it is highly unlikely that it has hurricane clips. When installing solar, it is a small investment to get it structurally certified and if required in your area, a building permit and inspection.

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