Inventor Allen Gezelman asserts that ballast-only solar attachment systems (BOSAS) are sub-optimal for high wind areas such as Florida and seismic-active areas such as California. As a result, Gezelman decided to come up with his own solution that he calls an adhered-ballast solar attachment system (ABSAS) that is designed for future low-slope California & Florida solar equipment installs.
We followed up with Gezelman for an explanation of the system.
“Florida Building Code only mandates designing roofs for 20-psf live load, which means that for the most part you cannot use ballast in Florida unless you really spread things out,” he said. “This is also true for many areas of the U.S. that use International Building Code (IBC) or variations thereof. Further, you probably cannot use perimeter (PZ2=66.6 psf) or corner (PZ3=103.6 psf) roof zones. I have been opposed to ballast for Florida for decades and have refused to do such designs until I invented the ABSAS.”
As Gezelman expains it, ABSAS combines the uplift resistance designed and built into the roof assembly, roof deck and building framing with the weight of a very modest amount of ballast to produce an aggregate uplift resistance that is more than adequate. The solar takes the wind force and transmits it to the building framing using a load path that passes through the roof assembly into the roof deck by adhering the bottom ballast block of each stack to the roof surface with Great Stuff foam-in-a-can.
String is useful
“We have used other, more expensive, foams and found the inexpensive HD Great Stuff works as well as any & better than some very expensive foam products such as Gaco Flash Foam,” he said.
Some examples of the ABSAS in action: The Children’s Services Council is in Boynton Beach Florida. The design wind speed in Boynton Beach is 170-mph. The calculated wind pressure for roof interior area (PZ1) is 37-pounds per square foot (psf).
Standard rail requires closer spacing.
Another is MLK in the downtown St. Petersburg area. Wind speed is for 145-mph. The contractor had to use deck plates and screws under the ballast stacks because in-situ testing showed that there was not a well-adhered load path from roof surface through to the roof deck.
“Plates and screws provided that load path. Further, the foam under the block water-proofed everything by encapsulation,” Gezelman said.
Another, Tierra Verde, juts out into Tampa Bay near the Skyway Bridge. Plates and screws were also needed on that job because the modified bituminous roof cap sheet pulled loose at 550-lbs during in-situ uplift tests.
9-ft c-c 4 in Cee roof attach
“California Solar Contractors will probably be interested in the results of testing on a Unirac BOSAS (ballast only solar attachment system), which I expect to retro-fit by injecting foam under the ballast trays and bottom blocks. This is probably a best practices solution for the headache California Solar Contractors will get when seismic resistance begins to be required for ballasted systems,” he said.
ABSAS offers a cost savings when you consider, on average, only one 32-lb ballast block is needed per PV module in Florida. Other ballast materials needed with ABSAS only about $15/module versus $50/module or more with other systems.
— Solar Builder magazine
[source: http://solarbuildermag.com/news/case-adhered-ballast-solar-rooftop-attachment-system/]
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