To my knowledge and in practice the term “isolated building” talked about during drills and included in CIDS was to let everyone know this building may be “out of the ordinary”.
The roof FFs know getting to roof may be tricky due to no adjoining building. LCC know they may be pressed to get very crafty getting acess to roof. A first due TL may leave spot for aerial to get ladder up, etc…
Is building isolated with only one stair? That would be on CIDS. Now roof guy knows he doesn’t have possibility of
A 2nd stair in different wing that might be used if not compromised by fire conditions in other wing.
Isolated building, single stair, rig can’t get to roof? now you’re taking the fire escape to roof. And all the challenges that taking that way brings. If fire conditions block the fire escape with access to roof, well now roof access isn’t happening until fire conditions are controlled to a degree that access can finally be safely