The Council on Tall Buildings and Urban Habitat  (CTBUH)—the international body that arbitrates on tall building height and determines the title of “The World’s Tallest Building”—has announced a change to its height criteria , as a reflection of recent developments with several super-tall buildings.
The new criteria wording—“Height is measured from the level of the lowest, significant, open-air, pedestrian entrance to…” allows for the recognition of the increasing numbers of multi-use tall buildings with often several different entrances at different levels, whilst also accommodating buildings constructed in non traditional urban or suburban locations. The CTBUH Height Committee has determined that the previous description of where to measure tall building height from—“Height is measured from the sidewalk outside the main entrance to…” is now no longer sufficient.
This will have an impact on both the height of tall buildings and their relative international height rankings. Burj Dubai, set to open as the world’s tallest building in January 2010, will now be measured from the lowest of its three main entrances (which opens into the entrance lobby for the tower’s corporate suite office function), while the recently completed Trump International Hotel & Towers in Chicago will be measured from the lower, publicly accessible Chicago Riverwalk. In the case of Trump, this additional 27 feet means that it will surpass the Jin Mao Tower in Shanghai to occupy the rank of 6th tallest on the current list of completed buildings.
“Beginning in 2007, with the knowledge that Burj Dubai would be significantly taller than any structure ever built, the CTBUH Height Committee met to review the criteria by which we recognize and rank the height of buildings,” said Peter Weismantle, Chair of the CTBUH Height Committee and Director of Supertall Building Technology at Adrian Smith + Gordon Gill Architecture in Chicago. “As one might guess, with the committee being made up of architects, engineers, contractors, developers, building owners and academics, a variety of opinions and views were expressed. The resulting revisions almost two years later reflect a general consensus of the committee in recognizing the most recent trends in tall building development around the world.”
Also in response to the changing designs and forms of tall buildings, the Height Committee has elected to discard its previous “Height to Roof” category. “The roof category just doesn’t make sense anymore,” said CTBUH Executive Director Antony Wood. “In the era of the flat-topped modernist tower, a clearly defined roof could usually be identified, but in today’s tall building world—which is increasingly adopting elaborate forms, spires, parapets and other features at the top of the building—it is becoming difficult to determine a ‘roof’ at all, even less so to measure to it.”
The tallest 10 buildings in the world as of November 2009 are shown in the diagrams below, ranked according to the three height categories now recognized by CTBUH. These are: (i) Height to Architectural Top, measured to the topmost architectural feature of the building including spires, but not including antennae, signage, flag poles or other functional-technical equipment; (ii) Height to Highest Occupied Floor, measured to the level of the highest, consistently occupied floor in the building (thus not including service or mechanical areas which experience occasional maintenance access); and (iii) Height to Tip, measured to the highest point of the building, irrespective of material or function of the highest element.
About the CTBUH
The Council on Tall Buildings and Urban Habitat, based at the Illinois Institute of Technology in Chicago, is an international organization sponsored by architecture, engineering, planning, and construction professionals, designed to facilitate exchanges among those involved in all aspects of the planning, design, construction and operation of tall buildings. The CTBUH is the world’s leading body in the field of tall buildings, and the recognized source of information on tall buildings internationally. It is the arbiter of tall building height and determiner of the title of “The World’s Tallest Building.” It maintains a significant database of built, under construction and proposed tall buildings.
More information on CTBUH height criteria can be found here .
The CTBUH recognizes tall building height in three categories:
Height to Architectural Top: Height is measured from the level1 of the lowest, significant, open-air, pedestrian entrance to the architectural top of the building, including spires, but not including antennae, signage, flag poles or other functional technical equipment. This measurement is the most widely utilized and is employed to define the Council on Tall Buildings and Urban Habitat (CTBUH) rankings of the Tallest Buildings in the World.
Level: finished floor level at threshold of the lowest entrance door
Significant: the entrance should be predominantly above existing or pre-existing grade and permit access to one or more primary uses in the building via elevators, as opposed to ground floor retail or other uses which solely relate/connect to the immediately adjacent external environment. Thus entrances via below-grade sunken plazas or similar are not generally recognized. Also note that access to car park and/or ancillary/support areas are not considered significant entrances.
Open-air: the entrance must be located directly off of an external space at that level that is open to air.
Pedestrian: refers to common building users or occupants and is intended to exclude service, ancillary, or similar areas.
Functional-technical equipment: this is intended to recognize that functional-technical equipment is subject to removal/addition/change as per prevalent technologies, as is often seen in tall buildings (e.g. antennae, signage, wind turbines, etc. are periodically added, shortened, lengthened, removed and/or replaced).
Highest occupied floor: this is intended to recognize conditioned space which is designed to be safely and legally occupied by residents, workers or other building users on a consistent basis. It does not include service or mechanical areas which experience occasional maintenance access, etc.