annexe, extension, take over, wing, annexment, annexure, annexer, additional, add-on, adjunction, more...

secede, detach, separate, divide

annexe, annexation, annexationist, annexationism, more...

non, new, statistical, secret, small, story, separate, present, confidential, special, second

building additions,   building wing,   building off of,   addition to,   another document,   added on to,   ranch add-on,   theater add-on,   building annexes,   add-on building