Council on Tall Buildings and Urban Habitat
CTBUH Height Committee Meeting
November 7, 2014
See the CTBUH Height Criteria
See more on the Height Committee
CHICAGO After a warm welcome and a brief review of the Height Committee’s duties and past actions from the Height Committee Chairman Peter Weismantle of Adrian Smith + Gordon Gill Architecture, the following topics were addressed:

Co-joined Buildings
There are a growing number of examples around the world of tall building complexes that share connections along their height (e.g. Petronas Towers, Arc de La Defense, Marina Bay Sands, and De Rotterdam). In some cases, it is difficult to assert whether to consider these projects as single buildings or multiple buildings. After much discussion, the Committee proposed the following criteria to clarify the status of these project types: “A building complex is considered to be a single, co-joined building (as opposed to two separate buildings connected by skybridges or other elements) when 50% or more of the total building height is connected. Exceptions to this 50% rule can be made in cases where the form of the building creates a coherent arch, creating a singular architectural expression and thus a co-joined building – to be judged by the CTBUH Height Committee."
The Height Committee at work
Completed Criteria
Current CTBUH completion criteria state that a building is not complete until it is: “1) Topped out structurally and architecturally, 2) Fully-clad, and 3) Open for business, or at least partially occupiable.” Yet some buildings are completed and occupied, while still not fully clad, due to remaining internal fit-out work requiring construction hoists to be attached to the building. Thus “fully clad” in the current CTBUH height criteria for completion is problematic. To address this issue, the Height Committee agreed to add a footnote to the fully-clad requirement acknowledging that construction hoists needed for fit-out will not affect a building’s cladding status. Also, the word “structurally” has been removed from the first item and moved to a footnote explaining that a building must be topped out structurally in order to be topped out architecturally. The new criteria thus now states:
A building is considered to be "Complete" (and officially added to the CTBUH Tallest Buildings lists) if it fulfills all of the following three criteria:
1) Topped out architecturally 1
2) Fully-clad 2
3) Open for business, or at least partially occupiable.

Footnotes:
1 The topping out architecturally of a building implies that ALL structural and finished architectural elements are in place.
2 The omission of a small number of cladding panels to allow fixing of a construction hoist while interior fit-out of some building areas is continuing does not affect the status of “fully clad.”
Gross-to-Net Building Height
In 2013, the CTBUH featured a Tall Buildings in Numbers report that compared and analyzed the proportion of unoccupiable to occupiable space in the height of in skyscrapers. The report referred to the phenomenon of completing a building’s architectural form with structure that is not intended to be inhabited as “Vanity Height,” a term that has since been viewed as too pejorative. To remain impartial, the Committee agreed to adopt the term “Gross-to-Net Height” to represent the proportion of occupiable to unoccupiable space in a building.
Engaged in discussion
Structural Definitions
Over the recent history of skyscrapers, the number of all-steel buildings has experienced a decline, largely because of the shift to regions outside North America as the predominant location for such buildings. Concrete and especially Composite-structured buildings have become more popular in these regions, composite systems involving both steel and concrete acting together compositely. The current CTBUH definition for “Composite” structural systems lacks specificity in terms of structural type and material use, with now a high percentage of new buildings being lumped together in this one category. More sub-divisions of this category need to be recognized, to be of more use to the Skyscraper Center user. The Committee assigned Terri Boake this task of developing subdivisions for composite structures, based on recognized, established terms, and consulting the structural engineers of the Height Committee for confirmation. The Committee also decided to consider allocating CTBUH funds to hire a student who would work with Boake to update this information and structural types for all buildings in the Skyscraper Center.
Attendees:
Peter Weismantle Director of Supertall Building Technology Adrian Smith + Gordon Gill Architecture/
Height Committee Chair
Joseph Burns Practice Leader, Managing Principal Thornton Tomasetti
Terri Boake Professor University of Waterloo
Kim Clawson Architect Aon FPE
Johannes de Jong Director – Products & Technology KONE Corporation
Jean-Claude Gerardy Manager ArcelorMittal
Marshall Gerometta Skyscraper Database Editor CTBUH
Russell Gilchrist Design Director Gensler
Mounib Hammoud CEO Jeddah Economic Company
Abdo Kardous Senior Vice Pres. / Mng. Dir. of Asia Pac. Hill International
Simon Lay Director of Fire Engineering AECOM
William Maibusch Project Executive DPR Construction
Mic Patterson Vice President Enclos
Robert Pratt Managing Director Tishman Speyer Properties
Mark Sarkisian Director SOM
Alfred Anton Seeling Regional Design Director Woods Bagot
Antony Wood Executive Director CTBUH