I would like to finish my 3rd floor attic, and make it liveable space for rental purposes as a 3rd bedroom for the upper unit apartment, with bathroom. As a Landlord, are there codes - laws for areas of exit, etc? What exactly is defined as liveable space? Adam

You have to contact your town's building department to find out the code requirements for living space.

Agreed, and yes there specific guidelines as to exits being properly marked, the need / placement of smoke or fire detectors and other guidelines to follow when converting part of a house into an apartment for rent. Always contact the city so that you don't have a lease terminated bya tenant who complains your unit isn't up to code!