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Quayside cool

PROJECT PROFILE: COMMERCIAL BUILDING George Demetri reports on Ove Arup's offices at Cardiff Bay

A new office building in Cardiff Bay combines well-designed brick construction with passive cooling in order to achieve a comfortable building with an eye-catching design. It is to the developer's credit that the prospective tenant was allowed considerable design input

Consulting engineers at the cutting edge of technology might be expected to choose a sophisticated cladding system for their own premises. Cladding which is at once attractive, durable, tried and tested, provides good value for money, requires little maintenance and has a thermal capacity to mediate the internal environment. So it cannot come as a surprise to hear that the very qualities sought by Ove Arup & Partners for the cladding to its new office in Cardiff Bay are embodied in the brick-faced cavity- wall construction which has been used throughout.

Ove Arup & Partners, having had a presence in Cardiff for some 28 years, now has a new Welsh headquarters which constitutes Phase 2 of the Scott Harbour development. Designed by Powell Dobson Partnership architects, the smart, purpose-built accommodation at Capital Waterside is located in the developing Cardiff Bay area and a stone's throw from some important landmarks, such as the spectacular nineteenth-century terracotta Pierhead Building, the new Welsh Assembly and Alsop & Lyall's elliptical sectioned Visitor Centre.

Developer Grosvenor Waterside was keen to allow the engineering practice - and future long-term tenant - to tailor the design to its needs in association with the architects. The result is a building which uses a traditional material - brick - not only to respond to the aesthetic requirements of the site in a cool, stylish modern idiom, but also to assist in the creation of a comfortable working environment.

Design aims

With a tight budget and the desire to avoid a cliched office block, the designers have aimed for a stylish building which combines efficient workspaces with a controlled internal environment. These ends were considered higher priority than either the cachet of expensive finishes, or superficial stylistic statements. What was required was a dignified architecture which made few concessions to the more usual commercial developments. But there was also a green agenda and one of the main reasons behind the choice of brick was to ensure good environmental control and avoid peak heat gains.

Construction

The three-storey building - completed in August 1998 - has been designed to complement the adjacent Scott Harbour Phase 1. Boldly asymmetric in both plan and elevation, it is arranged around a single core, offering 3,000m2 of accommodation for around 200 members of staff. The steel frame structure on piled foundations is clad with a 365mm thick cavity wall construction, comprising a single brick outer leaf, a 140mm block inner leaf and a 123mm wide cavity partially filled with 38mm foil-faced insulation. This achieves a U-value of 0.39W/m2degreesC. The thicker than normal cavity construction was necessitated partly by thermal requirements, and partly by the desire to maximise the set back of windows within the reveals, so that the full brick depth to the window face affords extra protection on an exposed site.

The pink buff brickwork looks welcoming in the well articulated elevations which also provide plenty of action, such as the hierarchy of opening shapes and proportions. The dynamic curve of the main block is achieved using standard stretcher bond, and the dramatic, cantilevered end wing on the main road elevation with its gently radiused end wall and knife- edge return clearly alluding to the nautical character of the site. Complementing the brickwork are crisply detailed reconstituted-stone dressings which further articulate the surface, as do mouldings in the same material placed above the highest line of windows in the same way a moulding might be placed above a traditional window head. To cap it all, a curved profile aluminium coping is used to complete the parapet.

Internal environment

The capacity of massive construction to benefit the internal environment has been understood since ancient times. In this case, a thick, insulated cavity wall provides a sufficiently long thermal lag - the time taken for solar heat gains to pass from the outside wall face to the inside. This lag was calculated by Arup to be 9.8 hours and has been used to stagger peak internal heat gains and so ensure manageable temperatures.

Further mass is provided by the attractively sculptured ceilings of exposed precast-concrete panels comprising alternating vaults and flats. Each 2.4m-wide vault is supported by a flat panel on either side. These in turn are suspended from 600mm-deep primary steel I-beams which also support the timber joists and chipboard floor above. The void created is used for services distribution and exemplifies the integration of structure and services.

The application of brise-soleil to office windows on the south and south east elevations has also boosted the passive cooling strategy. Positioned one third of the way down window openings, they perform a tripartite function: as a solar shading device; as a light shelf to reflect light through the top section of the window; and as an aesthetic feature. Further shading is achieved by the deep, 225mm window reveals which also serve to protect the windows from the prevailing south-westerly winds.

For those sweltering summer days and nights, the passive cooling is helped by the displacement ventilation supplied by a 70kW chiller. The idea is to remove the warm air emanating from people, lights and computers, and replace it by cooler supply air introduced through floor-level grilles aided by the generous floor to ceiling heights, averaging 3m, which allow the stratification of air conducive to a comfortable environment.

The essence of Capital Waterside Phase 2 is the combination of various technologies to produce a worthy building which fulfils the aesthetic, economic, technical and environmental aspects of the brief. In all these brickwork plays an important part.

Client

Grosvenor Waterside

Architect

Powell Dobson Partnership

Structural Engineer

Ove Arup & Partners

M + E

Ove Arup & Partners

Main contractor

Balfour Beatty

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