Go down to the Dept. of Building and Safety (see link) and ask to see the building permits for your property. Only permitted work is part of the building. If you did the work with a contractor who pulled permits, you can advertise it.
If you did not have the work permitted, in some cases you can ask if you can apply for one retroactively, but you may need to re-do work to bring it up to code. The moral to the story is that you should always try to do work with permits so it is covered by insurance (no permit, no proof that work was completed to code, for insurance purposes, it never existed).