The name carriage house today may refer to a single family home, a commercial building, or an outbuilding on a property with a main house.
Original carriage houses were outbuildings that were built to house horse carriages. Sometimes the horses lived in the same structure. Sometimes the caretakers for the horses and carriages lived in an apartment on the second floor. Some carriage houses were modest, others were elaborate. That might depend upon if the owner had one modest carriage, or 3 elaborate carriages that needed storage.
When I first moved to the east coast, I rented an apartment on a sprawling estate in Greenwich, CT. It was one of the actual original barns from this very large estate, with the original wood plank floors still intact on the second floor. Some called this place a carriage house. I called it a barn. I lived there when I first moved to the east coast from California. The concept of carriage houses, as well as mature trees and homes on acreage were all quite fascinating to me. Now that I have been in real estate for 10 plus years (NJ and FL) , carriage houses remain fascinating, but are no longer foreign to me.
Many land parcels in the northeast were subdivided, causing the former carriage houses to now become the only structure on a newly created parcel. Many of these carriage homes were converted to single family homes, and some retain much of their old world charm. In MLS listings and property descriptions, one can occasionally read the house style defined as a carriage house. Many carriage houses are, indeed, single family homes today. A few former carriage houses became zoned for commercial use after subdivision, and may now be the location of a coffee shop or retail store.
Still, other carriage houses continue to co-exist alongside main houses, never to have yet been subdivided and set free to exist on their own. The uses vary. I am familiar with carriage houses being used as extra garages, guest houses, and business offices located on the same property with a main house.
Sometimes you will find that the garage has been taken over by the carriage house, and they are now occupying both floors of the building, and it is no longer used as a garage. I hope that's helpful
In addition to the previous definitions, the description "carriage house" can also be found in new construction. Carriage houses are found in groups, just like townhouse communities. Carriage houses are one level-living and share a wall or walls. Groupings of two or four units are common. These homes are very popular in Western PA. You may be more familiar with the term "patio home".