Question-and-Answer Resource for the Building Energy Modeling Community
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I don't believe there is a way to do this in IES (or any other tools I'm familiar with) without some difficult post processing. To be honest, I typically just ignore that rule and allow for self shading for the baseline, based on what Cory said. As the example Rsunnam provided points out, this should be conservative (unless you're in a really cold climate). If the adjacent shading structures allow the baseline to be rotated, then the process of rotation effectively averages out any self shading, so to me those two requirements in App G are redundant.
The only thing I could think of in IES would involve a lot of post-processing. You would need to run a simulation without the adjacent buildings and without suncast, and then run a simulation with the adjacent buildings and with suncast. If you compare the solar gains (and also exterior conduction, though I suspect that will be smaller), you could then manually calculate what the cooling load should have been by subtracting the difference and recalculating the cooling energy. Of course that gets very complicated very quickly, because fans and pumps should be reduced too, and by that point you've basically modeled the entire HVAC system by hand in a spreadsheet or something, which is why I just ignore it.
It might, however, be possible to trick suncast into it, though I haven't tested it. You could do the same runs as above, and then compare the .shd files and manually edit it (telling suncast to run even though it thinks it's out of date). That again would take forever because those files are huge.
