The following language is adopted as a new Section 203:
"203. MEASUREMENTS
203.1 Scope.
Grade plane, building height, building area and floor area shall be established in accordance with Sections 203.2 through 203.5, respectively.
203.2 Grade plane.
With respect to each building, grade plane shall be a reference plane representing the average finished ground level adjoining the building at exterior walls. Where the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the property line or, where the property line is more than 6 feet (1829 mm) horizontally from the building, between the building and a point 6 feet (1829 mm) horizontally from the building.
Exceptions:
1. In no case shall grade plane be lower than the top of the established curb at the midpoint of the front property line of the lot on which the building is located.
2. For all structures on a zoning lot not exceeding 10,000 square feet (929 m2) in area, "grade," determined in accordance with Section 17-17-0265 of the Chicago Zoning Ordinance, shall be allowed to be used as grade plane.
203.3 Building height.
Building height shall be the vertical distance from grade plane to the mean elevation of the highest roof plane. For purposes of this code, building height is not the same as mean roof height.
Exceptions:
1. Building height shall be measured to the highest walking surface of an occupiable rooftop located above the highest story.
2. Building height shall be measured to the top of a parapet wall that exceeds 42 inches (1067 mm) above the highest point of a low-sloped roof or occupiable rooftop.
3. Unoccupied rooftop structures shall not be considered in determining building height in accordance with Section 1510.1.1.
4. Rooftop access penthouses and other rooftop structures associated with occupiable rooftops shall be considered in determining building height in accordance with Section 1513.
5. Dormers that do not have a low-sloped roof, are no higher than the highest point of the roof plane in which they are located and do not exceed one-third of the horizontal area of the roof plane in which they are located shall not be considered in determining building height.
6. For buildings without low-sloped roofs or occupiable rooftops, building height may be measured to the mean elevation of all roof surfaces above the finished floor of the highest story.
7. Where there is no occupiable rooftop above and the highest roof plane is provided with continuous insulation installed entirely above and not exceeding 12 inches (305 mm) in height above the structural roof deck and required parapet walls, building height may be measured to the highest point of the structural roof deck.
203.4 Building area.
Building area shall be the sum of the horizontal area included within surrounding exterior walls, or exterior walls and fire walls, exclusive of courts for each story above grade plane and the horizontal area of mezzanines, equipment platforms and lofts. Areas of the building not provided with surrounding walls, such as patios and exterior balconies, shall be included in the building area if such areas are included within the horizontal projection of the roof, floor or walking surface above. The floor area of basements shall be included in building area where required by Section 506.1.3.
Exception: The horizontal area of the portion of any story, mezzanine or loft with a ceiling height of less than 5 feet (1524 mm) shall be excluded from the calculation of building area.
203.5 Floor area.
Each reference to "floor area" in this code shall mean gross floor area unless the provision specifically references net floor area.
203.5.1 Gross floor area.
Gross floor area shall be measured in the manner provided for determining building area in Section 203.4 with a further deduction for the horizontal area of shafts without openings and the thickness of interior walls enclosing such shafts. There shall be no deduction for corridors, stairways, ramps, closets, mechanical rooms, elevator shafts, toilet rooms, the thickness of interior walls, columns, or other features.
203.5.1.1 Separated mixed occupancies.
The gross floor area of a mixed occupancy separated in accordance with Section 508.4 shall be the horizontal area included within surrounding exterior walls, fire walls and fire barriers. Areas of the occupancy not provided with surrounding walls, such as patios and exterior balconies, shall be included in the gross floor area if such areas are included within the horizontal projection of the roof, floor or walking surface above.
203.5.1.2 Unseparated mixed occupancies.
The gross floor area of an occupancy that is not separated in accordance with Section 508.4 shall be measured to the centerline of interior walls and partitions that separate the occupancy from other occupancies in the same story.
203.5.2 Net floor area.
Net floor area shall be the actual occupiable horizontal area, not including columns, permanently attached equipment and furnishings that are 28 inches (711 mm) or greater above the floor, the thickness of interior walls and unoccupied accessory areas such as aisles, corridors, stairways, ramps, individual wellness/lactation rooms, toilet rooms, mechanical rooms and closets."
(Amend Coun. J. 7-24-19, p. 3646, § 25; Amend Coun. J. 2-19-20, p. 14473, Art. II, § 2; Amend Coun. J. 6-25-21, p. 32180, Art. II, § 2; Amend Coun. J. 1-26-22, p. 43756, Art. II, § 2)