The need for constant communication in a continuous market room and the ability to expand it to three times its initial size dominated the Lloyd’s brief. There was also the difficulty of dealing with internal circulation loads, especially at peak times like the daily lunch exodus from the building. Productivity issues dictated a high level of occupant comfort. Finally, the solution had to be flexible enough to change function from office to market and back again without disrupting ongoing activities.
As the design emerged, the magnitude of internal heat gain from people, lights, and equipment soared above the conventional 3 or 4 W/ft2 all the way past 13 W/ft2 in the market room and over 12 W/ft2 in the office areas. In part, this was due to the manner in which Lloyd’s operates the trading floor. Moreover, it became evident in the late stages of design that computer technology would have to be incorporated into the workstation environment. This led to a doubling of the electrical power needed and to an attendant increase in mechanical cooling capacity.
Fitting the required building area into the irregularly shaped site was further complicated by the close proximity of adjoining building foundations. Right to Light laws that protected existing buildings from the shadows of new construction carved into the vertical deployment of the building volume. Old London’s urban context created a difficult backdrop for Rogers’s expressionistic ideals.
Among the many challenges shaped by the design propositions, the visual legibility of building parts seemed most critical. Exposing structural and mechanical components required careful consideration and craft in their fabrication and connection, greatly exceeding that necessary when these parts are simply covered up by layers of finish materials. The constraints of one system would affect the attributes of others in unexpected ways. Ultimately, systems such as glazing and interior light fixtures were developed exclusively for the Lloyd’s building. Other systems had to be mocked-up at full scale and tested off-site. Weatherizing and cleaning externally exposed pieces had to be considered in practical as well as aesthetic terms (compare Lloyd’s with Pompidou in this regard). At the macro-scale, London’s cool climate threatened to invade any open-skinned expression of unbroken interior space.
The atrium in particular threatened to be an environmental problem. Fear of cold drafts flowing down the glass surfaces and spilling across the floor of the market room led to an engineering investigation. Members of Ove Arup’s office performed one of the first architectural uses of computational fluid mapping to test the situation. They concluded, somewhat ironically, that warm air rising from the intense level of activity and use of equipment in The Room would more than offset the effect of heat loss against the glass.
Appropriate Systems
The service towers that surround Lloyd’s are undeniable references to Louis Kahn’s “served and servant” articulation of function. As in Khan’s Richards Medical Research Building in Philadelphia and the Salk Institute in San Diego, the towers organize and facilitate the functional design scheme. The formal precedent of George Street’s Law Courts is likewise reflected in the skeletal expression of the service towers. As a continuum of Rogers’s own work, the exterior expression of services and uninterrupted expanse of interior space are clear carryovers from his work with Renzo Piano on the Centre Pompidou.
With cramped perimeter boundaries and Right to Light- restricted height setbacks, there was no where to go but down. The approach to Lloyd’s and its boundaries are so limiting that delivery trucks have to be taken by 10 ton and 24 ton elevators to the lower of two basement levels for unloading. Cooling towers were placed on the roof because there were no other outside areas available. There is no on-site parking.
A clever separation of public and private circulation is achieved by raising the business entry a half-level above the street and opening a pedestrian mall around the level below the street. The public spaces on the lower level connect to Leadenhall Market and to a street-level passage called “The Green.”
Enclosure of the gallery floors uses 2.2 acres (8903 m2) of a double-pane outer glazing and a single pane inner panel. The insulated unit outer glazing is 0.25 in. (6 mm) rolled glass outside plus a 0.5 in. (l2 mm) air space and a 0.25 in. sheet inside. The inside layer of glass is a 0.25 in. (6 mm) pane of rolled glass. Glazing is set in a thermally broken aluminum frame and braced with perforated aluminum fins on the exterior. The 1.6 in. (40 mm) void between the two glazings is used as a return air path to warm the interior glass surface during cold days and aid thermal comfort close to the exterior wall. The outer insulated glass unit was developed by RRP as a translucent daylight lens with rolled facets or “dimples” that refract light and scatter it at different angles.
Infill panels on the gallery block, located at the raised floor level and penetrated by air ducts, are of epoxy-coated and linen-textured stainless steel. The prefabricated toilet modules, the satellite tower cladding, and the elevators are surfaced with the same material. The epoxy coating was developed for steel bridges and is expected to be maintenance free for more than ten years.
The 224 ft X 153.5 ft (68.4 m X 46.8 m) gallery is framed by poured-in-place concrete columns on a 35 ft by 59 ft (10.8 m by 18 m) grid. Eight interior columns form three center bays of 35 ft by 35 ft (10.7 m), above which a glazed steel frame atrium rises to the full 13-story height. Glasssided escalators, reminiscent of Norman Foster’s Willis Faber Dumas building, run up and down two levels from the double-height market room. The all-important Room market level is a double-height version of the typical 9.8 ft (3.0 m) floor-to-ceiling office floor. Three gallery levels above The Room extend the market area vertically and
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Figure 10.23 One of the six service towers. |
keep communication and walking distances compact.
Horizontal construction in the gallery is made of a two-way grid of 21.6 in. deep by 11.8 in. wide (550 mm X 300 mm) beams at 5.9 ft (1.8 m) on center both ways. The floor grid is supported by posttensioned U-beams spanning between the columns and ending in precast yokes resting on precast brackets at the column support. A return air plenum and service void is created by 17.3 in. (440 mm) high stub columns that rest on the grid intersections and support a 3.9 in. (100 mm) concrete deck above. Custom-designed light fixtures fill the 10,000 ceiling voids, 59.1 in. (1.5 m) on each side, and are suspended inside the grid beams below.
The atrium vault and exterior glazing are of exposed structural steel frame. The atrium glass is set in an external space frame tubular steel barrel vault. The barrel vault springs from a custom-cast steel bracket bearing on top of the concrete columns. Satellite towers were constructed from about 1800 precast concrete frame pieces.
The served-and-servant configuration pulls virtually all mechanical elements out of occupied space. Toilet rooms, elevators, electrical and plumbing risers, even firemen’s lifts, are located in the towers. The toilet rooms were prefabricated as complete modules in Bristol and delivered ready to plug in.
The mechanical plant is in the lower basement level, and the cooling towers are on the roof. Distribution of air to the market room is accomplished from the basement level up through floor registers. Air for the remaining gal-
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Figure 10.24 External ductwork. |
leries comes from three-story fan rooms located on top of four satellite towers. Vertical air distribution runs down the towers on the exterior of the elevator lobby windows. Horizontal supply and return air ducts of up to 24 in. (610 mm) diameter finger across the facade at every level at the base of each floor. Supply feeds into the floor plenum. Return draws air up through the light fixtures, across the stud column service void, through an exterior fishtailshaped extract duct, down the window cavity and into the duct. All exterior ductwork is clad in stainless steel.
Inside, the gallery ceiling-to-floor service layer is divided into three physically separated zones totaling about 45 in. (1.1 m) in thickness. First is the concrete ceiling grid continuously in-filled with a combination return air, fire sprinkler, and light fixture. Above that is the void between the stub columns provided for horizontal distribution of services and as a return air plenum. Finally, above the concrete deck, an 11.8 in. (300 mm) raised floor is left as a service way and provides a supply air plenum.
Some 1600 local fan terminals in the raised floor distribute air to the market areas. They mix 50 percent room air with 50 percent primary (supply) air and deliver it to as many as four workstations. There are also 900 perimeter water-to-air heat pumps using chilled water return lines from the fan rooms atop the service towers as a heat source in the early part of cold days.
The expressionist notion of articulating the systems externally is echoed on the interior. Exposed structure forms the ceiling grid, whose cells are completed by the sophisticated lighting fixtures. Most partitions are eliminated, leaving the exterior glass wall as a translucent boundary. The floor consists of finish surfaces over the 23.6 in. X
23.6 in. (600 mm by 600 mm) raised floor panels.
The only principal interior element consists of a custom-designed modular workstation. It is readily demountable and easily connects to distributed services beneath the floor panels. Each workstation provides individual controls for task lighting and air distribution.
Technical Integration Highlights
• Terraced floors above the sixth gallery level promote maximum use of the site and conform to Right of Light requirements.
• Deployment of service towers around the rectangular gallery fill the odd corners of the irregularly shaped site and maximize its utilization.
• Uninterrupted interior space is provided by pulling services to exterior service towers.
• Separate ceiling return air and raised floor supply air plenums eliminate interior ductwork.
• Light fixtures combine return air and fire sprinkler hardware.
• The expression of technical elements lends scale and clarity to the elevations.
• Service towers break up the regular surfaces of the rectangular glass-box gallery.
• A visual dynamic plays between the static box and the apparatus-covered towers.
• Craft in fabrication of exposed structure and mechanical elements creates a machine aesthetic.
• Tight security is provided by elevating the guarded business entry at a half-floor (8.2 ft or 2.5 m) above the street and leaving an exposed public walkway around the retail and restaurant floor a half-level below. This also creates a strong pedestrian connection to the Leadenhall Market.
• The air distribution plenums couple the heat capacity of the structure with the thermal needs of the space, provide a large thermal buffer for the cooling system, and reduce supply air temperature requirements.
• Return air cavities in the exterior glazing alleviate cold glass walls.
• Fire water storage tanks double as thermal storage reservoirs for the heating system.
• Service distributions under the raised floor are accessible for reallocation of market spaces or workstations.
• Service equipment is accessible for repair or replacement upon obsolescence.
• Return air light fixtures remove 60 percent of the convective heat from the lamps before it ever enters the room as a cooling load.
Lloyd’s makes a decidedly Gothic impression. Richard Rogers’s reference to Street’s Law Courts in the Strand as a formal precedent seems well served by the six technical service towers, or “turrets” as Rogers has called them, that spire around glass walls and gleaming fishtail ducts. The building even responds to Rogers’s desire that different views provide surprises “rather like a Gothic cathedral.” Lloyd’s’ visual expressionism conveys the mechano – rationalist interworkings of its architectural systems very explicitly—and this is probably the most obviously integrated building anywhere. It suggests technical integration like a red race car suggests tire-burning velocity. Service towers beyond anything Kahn could have possibly foreseen, exposed structure, exposed ducts — all the visual integrations are marshaled together around their shared mandates. Is this unified visual result the best measure of integration, or are performance factors the deeper and more critical outcome? The window wall is a return air duct after all; the light fixture is an acoustical ceiling; desks become personal air diffusers; every part of the building does two or three things. Or perhaps it is less a matter of features than of benefits: flexible space, technology uptake, folded space, personal comfort, site utilization, energy efficiency, and so on.