Peak condition.

An ambitious airport terminal intended to give a sense of celebration to arrival and departure and to invigorate the economy of Colorado.

You wouldn't expect to find the largest international airport in the US within sight of the Rocky Mountains at Denver, but there it is, five runways, high speed trains, parking for 12 000 cars and the huge 275 m (900ft) long terminal building by C.W. Fentress, J.H. Bradburn & Associates. If the main thing about the airport is its terminal, the main thing about the terminal is its roof.

Denver mayor Frederico Pena asked the architects of the new airport (which replaces the 65 year old Stapleton International) to make a building that would be a symbol for the city and they responded by suggesting a white fabric roof formed into peaks as a conscious echo of the snow-capped skyline of the Rockies that form a dramatic backdrop to the plateau.

It is at the moment the largest tensile roof structure in the world and has been created to cover the Great Hall, the central space of the terminal. It is intended to make the place legible to all users, and all the common functions of the complex: general waiting, shops, restaurants and so on are grouped in and round it.

Functionally, the airport is a model of clarity. Passengers arriving by car are received under fabric canopies (foothills of the peaks over the Great Hall) that fringe the outside of the sixth level. From here, they pass through ticketing and check-in areas to arrive on balconies lined with restaurants overlooking the big space on level five. (Passengers arriving by public transport have a rather more complex journey, for they arrive at level five and have to go up to check in before descending again to the Great Hall). From the Hall, they go down to the platforms of the high speed underground shuttle that takes them out north to the concourses (by Allred, Seracuse, Lawler/TRA) that stretch out as thin fingers east and west of the rail spine. The concourses are dull, utilitarian affairs of seemingly endless boarding and reception areas strung out in regular lines.

Arriving passengers go through the dreariness of the concourses in reverse, enter the train from which they ascend to the Great Hall, from where they can pass through the walls of shops to collect their luggage (when the $193 million automated baggage handling system starts to work properly). After collecting bags, they move to the buses, or to the multi-storey car parks which fringe the terminal on both sides like rather stolid strata. International passengers have to go through a rather different route, being received in a comparatively small baggage handling area to the north and going through immigration and customs checks before entering the Great Hall. Although Denver is categorised as an international airport, international traffic is expected to form quite a small proportion of its trade. Its raison d'etre is as a US hub and the promoters hope to achieve for Denver and Colorado the regional boom that brought great prosperity to Atlanta and Dallas/Fort Worth in the 1980s; when it all works, with new techno-industrial developments to the south of the terminal attracted and running, the promoters expect that the airport complex will have a higher gross domestic product than several European countries. But 'when' is questionable - the airport has not been used yet (latest projected date of opening is 28 February), and many aviation experts believe that it is far too big.

No-one remembers the Texas or the Georgia airports as places of arrival and departure, but for all the dumb moments, stolid base and flashy internal finishes, a visit to Denver's Elrey Jeppesen Terminal will be an event because of the roof (which was designed with structural engineers Severud Associates). Fabric was chosen for lightness and speed of erection as well as its picturesque qualities. The peaks are created by 34 steel masts. placed in pairs 50 m (150 ft) apart with 20 m (60ft) between each pair. The fabric swoops between the peaks and is tensioned by cables following the ridges and the valleys. With ridge cables taking, downward thrusts of snow and selfweight and the valley ones resisting upward forces from the wind. A third set of cables is included for reinforcement. Arranged about 12 m (40ft) apart and perpendicular to the ridge and valley network, these are encased in fabric sleeves and attached to the outer membrane. They are intended to take stresses when a pane of fabric has to be replaced.

The roof is in fact composed of two layers of fabric, both of woven fibre-glass coated with Teflon. The outer layer is the primary tensile structure, while the inner one helps create an acoustical barrier, conceals the clumsy seams of the outer one and, by generating an air space which varies from 400 mm to 1600 mm in width, helps to provide thermal insulation. The crucial detail in any fabric roof which has to be sealed to a stable structure is the nature of the joint between the two. Above the ticketing counters, there are triangular clerestories of glazing that bring glimpses of the sky to the Great Hall. The upper edges of these are connected to the fabric (which moves up and down at this point by 75 mm) with pneumatic tubes that expand and contract as the fabric flexes. A similar detail is used over the big glazed walls at the north and south ends of the Great Hall, where the sections of the steel members are kept slender by stiffening the whole structure with horizontal bowstring trusses.

Such a large and ambitious terminal merits comparison to the best new equivalents elsewhere. In clarity of organisation, it rivals the much smaller Startsted (AR May 1991) and the much larger Kansai (AR November 1994), but it lacks their clarity of progression, in which passengers move in a poetic and orderly visual sequence from land to air sides. And it lacks their clarity of architectural expression - even though there are in effect two buildings at Kansai, the inner one is completely subsumed within the shell. In Denver, the exciting roof sits on top of and among dull support buildings - but it is unforgettable nonetheless.