In one- or two-family dwellings, an exception can be made for the ban on full bathrooms in cellars if certain requirements are met. Full bathrooms, or three-fixture bathrooms, are bathrooms containing a lavatory, a water closet and a shower or bathtub. According to Buildings Bulletin 2011-010, in order for a cellar of a one- or two-family residence to qualify for a three-fixture bathroom, the cellar must be open without partitions and have direct access to the residence above and the outdoors. The cellar must also be equipped with smoke and carbon monoxide detectors and without any other fixtures. If the cellar contains a boiler room, the boiler room should be enclosed with one-hour fire-rated construction and properly ventilated. If the cellar contains a garage, the garage should be separated from the cellar.

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