Tar and gravel is especially bad for ballasted racked PV systems.
I think I would be mostly worried about if it is going to leak or not.
What do you mean by ballasted racked PV systems ? Do you mean held in place by weights ? Trying to get the pro's and con's about different roof systems and having PV systems attached to them ...
Yes, that is what I mean. Ballasted racking systems depend on evenly distributing the weight of the array under the pans that hold the concrete ballast blocks. Tar and gravel roof surfaces concentrate the array weight into point loads where the pans are in contact with the individual rocks, so they are more prone to causing leaks.
I wonder if that is allowed by Florida building codes ?
You could research that. I rather doubt that code actually speaks to it directly. It probably comes down to having a reputable engineer stamp a design and the AHJ accepting the engineering. Since the design windspeed will have to be the max in Florida (hurricanes) as compared to some other places, having enough weight to hold down the system is something which the roof would be less likely to support (may or may not be solvable with reinforcement). FWIW I recall a ballasted racking manufacturer touting their systems surviving hurricane Maria in Puerto Rico in 2017; I realize PR is not FL. Also FWIW in California you don't need as much weight for the wind uplift but the have additional requirements (attachments and/or distance from edge of roof) because they are worried about the whole thing sliding to the edge of the roof in an earthquake, which they may not worry about in FL.
Yeah I dont think it is black and white. I have worked on quite a few ballasted systems and most of them have at least a few attachments. You can have more attachments and less ballast or vice versa, or both if you are modeling a high wind speed.
