For a space with a ceiling that increases in height as the distance from the operable openings increases, how is the ceiling height (H) determined for use in the natural ventilation distance formulas of Sections 402.2.1.1 through 402.2.1.3?

• The maximum ceiling height in the space.
• The ceiling height at the midpoint between the operable openings.
• The average height of the ceiling within 20 feet from the operable openings.
• The minimum ceiling height in the space.