25 May '12, 10pm
The challenge? How to safely support the weight of a large solar-electric array atop a 100-year-old barn structure.
With the engineer’s stamp in hand, the second hurdle was how to work on a steep corrugated metal roof. Since we would be connecting our safety harnesses to the racks and walking on them a lot while building the array, they needed to be stronger than typical aluminum PV mounting rails. We designed a system using steel Unistrut bolted through the roof to another piece of Unistrut on the inside of the rafters, sandwiching the roof between them. For the topmost section, where the slope was not as steep and the force on the rails wouldn’t be as great, Spax engineered lag screws secured the Unistrut Rails to the rafters. Where each bolt penetrates the metal roof, a steel spacer holds the rail off the roof surface; a neoprene washer, sealed with silicon sealant, is used against the metal roof. This is not suitable for a residential roof (we always use fully flashed feet rather th...