In addition the windows have to be no more than 45" from the floor and adequate for escape in case of emergency. I've seen some basements that have a small transome window near the top of the wall, that isn't adequate for living area. MikeY

There has to be proper ingress and egress, i.e not having to go through a room such as storage,furnace,or laundry room that's not part of the actual unit, to exit the apartment.. You have to have windows in each bedroom that open for natural ventilation and light.If you remodel an existing basement into an apartment that wasn't previously one you have to take out a building permit