There is no straight yes or no answer to this question, but in some cases full (three-fixture) bathroom can be permitted in the cellar. Only Licensed Architect can give you the final answer to this question, but we will make an overview in this article.
The first question would be whether your cellar is legally a cellar or a basement. If the floor is located underground by more than a half – then it is a cellar, if not – it is a basement or a ground floor.
The second question would be what types of uses does the Certificate of Occupancy of the Building lists on that floor. If there is any mention of “Living” or “Habitable” rooms or “J-3 Occupancy” or “R-3 Occupancy”- then chances of getting a new bathroom are higher, If it lists only “Garage”, “Boiler room” – your chances are medium. If your property is located in the Flood Zone – then your chances are minimal.
If your CO (Certificate of Occupancy) lists only “Boiler Room”, “Garage”, any other “Accessory spaces” – then in order to design a bathroom there, we must comply with several conditions: Cellar shall have open plan, have a direct access to outdoors, shall not have any other plumbing etc.