November 2000

/CNAC Building

Classical symmetry

Hong Kong is full of glass boxes -- those reflective uniforms in silver, blue or black that dot the skyline on both sides of the harbour. Adoption of a modernist idiom, however, need not translate into anonymity and blandness.

At Chek Lap Kok international airport there is a model of classical symmetry which is modernist in expression but by no means pedestrian.
        The six-storey high Dragonair/CNAC Building, developed at a total project cost of HK$1.4 billion, consists of two identical but separate blocks linked together by a four-storey high atrium. An external colonnade of stainless steel-clad columns provides a vertical counterpoint to the horizontality of the overall design, responding to the call for form to follow function with an easy poise.
        The building's location, on a 1,440 sq m site overlooking Tung Chung Bay in the eastern corner of the airport island, immediately posed three challenges for the architect: height restriction; aircraft noise; and a corrosive seaside environment.
        The solution to these challenges, as developed by architect Wong Tung & Partners Ltd (WTPL), is a simple yet elegant one.
        The need to comply with height restrictions imposed by the glide path generated a low building which is rectangular in plan and modernist in expression but with classically derived proportions. The two wings on either side of the atrium form pavilions defined by the projecting roof element while the Flight Training Centre to the east of the office pavilions terminates and defines the forecourt space.
        The road system, according to WTPL architect Edward Billson, forms a perfect hippodrome of Roman proportions.
        The common atrium gives access to the main lift lobbies which by necessity are located at the end of the rectangular footprint, thus creating large, open office floors which provide maximum flexibility in terms of layout.
        The problem of aircraft noise was addressed by the adoption of a double-skin cavity wall system which provides 60 dBa of sound attenuation. A 800 mm cavity separates the 19 mm thick external layer of fully-tempered glass and the inner layer, which is an insulated low E coated unit.
        According to Mr Billson, acoustic engineers required three layers of glass with a minimum of 200 mm between two of the layers. The cavity wall system not only answers the engineers' requirements, but also avoids condensation problems through its use of acoustic baffles to ventilate the system. The cavity also facilitates maintenance and improves the building's thermal performance.
        Although studies in the US have indicated that natural light enhances productivity, clear glass is rarely used in Hong Kong both because of concern for the visibility of internal chaos, especially in strata-title buildings; and concern for the view out of the building, which is not always a pleasant one in urban Hong Kong.
        The Dragonair/CNAC Building, however, proves ideal for its application because of the spectacular views of Tung Chung Bay and the peaks of Lantau as well as the fact that it is an end-user building in which the interior layout can be coordinated. The low E glass used increases light transmission to 50 per cent, compared with 15 per cent for reflective glass while maintaining the same shading coefficient. The interior was carefully planned to ensure that workstations sit away from the glass line.
        "We believe the benefits of a large view and natural lighting outweigh concerns for not being able to put storage against the external wall," said David J Clarke, deputy director of WTPL.There are other advantages to the choice of cladding material - glass is also the best material for resisting the corrosive effects of a seafront environment, and the clear glass fits the airport's low reflectivity requirement for all structures.
        Several devices were employed by the architect to achieve the desired sense of lightness for the building.
        The choice of clear glass is complemented by the method for fixing the curtain wall, which is hung from Level 5 rather than supported on every floor. By thus separating the building volume from its skin, both the sense of volume and transparency are enhanced.
        Much thought was also given to the form of the brushed stainless steel pilotis and the roof. The slender, 25 m high pilotis were designed with entasis and therefore taper slightly from the middle to the top and bottom. To create an illusion of lightness, they are lit at the bottom, but not at the top. The large floodlights at the base of the pilotis also throw light into the stainless steel soffit.
        "The idea of the lighting is to get the building to glow," Billson explained. "The top of the pilotis is not lit because we wanted the roof to float, seemingly unsupported, above the pilotis and the building."
        Mr Clarke said the intention was to make the roof look almost as thin as a folded card. To achieve that sense of lightness, every effort was made to keep the roof free of electrical and mechanical installations. Thus, lift machine rooms are provided in the basement while the adjacent crew facility building is used to accommodate chillers which are connected to the main building through pipelines running through at the basement level.
        Upswept and projecting beyond the facade, the roof evokes images of Chinese eaves for some but also invites the inevitable allusion to flight.

section A-A

        "Our intention was to look at things of quality at the airport and pick up the vocabulary and materials without aping its imagery," Mr Clarke pointed out. "We deliberately avoided the aerofoil cliche but at the same time the design called for a strong yet simple roof expression." Light also suffuses the 20 m high, 24 m wide and 26 m deep atrium through a louvred ceiling and mast-supported skin walls. The 4.2 m by 1.5 m laminated glass panels are bolt-fixed to a system of steel outriggers which are supported in turn by the prestressed mast structures at 4.5 m centres. Design of the mast, which is reminiscent of the masts on sailboats, required a lot of engineering input, but the result is a support system which employs the most minimal amount of steel to support the maximum area of glass. Mr Billson said it was an environmentally responsible solution as it makes the most efficient use of non-renewable resources. Aesthetically it also continues the vertical rhythm of the pilotis across the atrium connecting the two buildings.
        The atrium is described as an interstitial space which allows the typical office to "break out" through a series of balconies that look down on it from different perspectives. A sense of airiness was achieved through the use of glass and the innovative fixing system, which are complemented by a light colour palette, creating an ice cube where the sense of freedom associated with the outdoors can be experienced in the air-conditioned comfort of the indoors.
        The building is set on a cleft travertine plinth sourced from Mariotti, a respected stonemason in Italy. Extending into the public space beyond the building, the plinth is part of the architect's careful orchestration of the user's experience of the project. This plan envisages the user approaching the building via the big, open space paved by the rough hewn stone and move towards the medium space defined by the pilotis. Finally the user reaches the intimate space established by a ground floor which sits back underneath a 7 m first floor cantilever that provides weather protection without spoiling the sleek facade.
        In addition to a quiet working environment, the view and natural lighting, Dragonair and CNAC staff also benefit from recreational facilities which include a fitness centre -- described as having one of the best views of all fitness centres in Hong Kong -- a 25 m long swimming pool; a sports hall for ball games and aerobics; a number of lounge areas; a reading room and a cafeteria which seats 400.
        The 32,500 sq m of total gross floor area includes a separate training block which houses a safety training module for cabin crew; a flight simulator unit for A320 aircraft (provision is made for one more simulator at a later date); inflight services mock-up; and lecture and debriefing rooms.

client Dragonair & CNAC (Group)
architect Wong Tung & Partners Ltd
project management Ove Arup & Partners and CITIC Project Management
contractor AMEC-Hong Kong Construction Co Ltd Joint Venture
structural engineer Maunsell Consultants Asia
m&e engineer J Roger Preston Ltd
facade technology Meinhardt Facade Technology (HK) Ltd
quantity surveyor Davis Langdon & Seah

-- Building Journal