Owners of homes with underground floors frequently ask if it’s possible to build another bathroom there. The answer entirely depends on whether it’s a basement or cellar.
Although the two terms basement and cellar are largely interchangeable in everyday English, they’re distinctly different terms according to the Department of Buildings (DOB). A basement is at least 50% above grade and is considered a “habitable space” by the DOB. If it meets certain code requirements, it can serve as a bedroom or an entire apartment unit. As such, it can accommodate a bathroom.
A cellar, which is at least 50% below grade, may have a half-bathroom, but in most cases, it may not have a full, three-fixture bathroom. This is because a cellar is not considered habitable space. It can be renovated to accommodate certain household functions—for instance, a rec or storage room—but its official utility is fairly limited. Since it’s illegal for people to live in the cellar anyway, there’s generally no need for them to have a full bathroom.
However, note above we wrote “most cases.” In some cases, one- and two-family houses can have a full bathroom in the cellar. However, it must meet the following criteria given by the DOB:
- The cellar is open without partitions except for enclosures for:
- a boiler room
- a laundry room
- windowless storage and/or utility rooms limited to less than 60 square feet
- The cellar is connected via an unenclosed stair to the residence above, as well as direct access to the outdoors via stairs and an operable door
- The cellar is equipped with smoke and carbon monoxide detectors
- The boiler room is enclosed with one-hour fire-rated construction and properly ventilated
- If the cellar also contains a garage, the garage must be separated from the cellar by one-hour fire-rated construction.