1 -- The living area of this type of residence is confined to the ground floor. The headroom in the attic is usually too low to be used as living area. 1.5 -- The living area in the upper residence is 50% to 90% of the ground floor. The upper level has a peaked roof and/or dormers. The living area of the residence is the sum of the ground floor plus the area on the second level with a ceiling height of 6 feet or more. 2 -- In this type of residence the second floor area is equal to or nearly equal to the ground floor area. The total living area is the sum of the ground floor area and upper floor area. 2.5 -- This type of residence has two levels of equal or nearly equal area and a third level which has living area approximately 50% of the first floor area, with a ceiling height of 6 feet. The total living area is the sum of the ground floor area, second floor area and area on the third floor with a ceiling height of 6 feet or more. Bi-level or Split-Entry -- This type of residence has two floors of living area, one above the other. One area is about 4 feet below grade and the second is about 4 feet above grade. Both areas are approximately equal in size. Both levels have full ceiling heights. The living area is the sum of the lower level area and the upper level area. Tri-Level -- This type of residence has three levels of living area, one at grade, one about 4 feet below grade and one about 4 feet above grade level. All levels are originally designed to serve as living areas. All levels have full ceiling heights. The living area is the sum of the area of the three levels.
In a tri-level home, the foundation is the area beneath grade level.