Your building department will have all the specifications it requires. There are several important requirements like ceiling height and a safe egress aside from the interior stairs. Its VERY important to get a building permit and comply with the municipality for both safety and insurance reasons.
You might be able to call the town clerk and get that information. Once a mortgage is granted on a property, it is recorded on the public record. If not, you might want to try a local real estate agent to see if they can find out that information for you. Good luck.
Century 21 Princeton Properties