February 24, 2016
Why would you want to use an imaginary property line if there is an actual one there? The openings on your building are governed by Table 705.8 IBC or whatever code was applicable when you constructed, same with your neighbor and those are based on FSD to the property line. Someone may have allowed something they shouldn't have, and now they are now trying alleviate the situation.
July 12, 2017
Is there any restriction on the distance to (or the percentage of openings in) a facade built near the property line, where the adjacent property has a building also very close to the shared property line? It has several unprotected, un-sprinklered openings, and someone has indicated I may be required to use the imaginary line rules (applied to the neighbor's building) in setting the distance of my building to that building. I thought the imaginary line was only for buildings on the same property. My understanding is that since you can't control what happens on adjacent properties, you only had to concern yourself with your own building and it's distances and opening percentages relative to a property line. Maybe I'm wrong. This is in California.