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Nottingham Contemporary art gallery: Engineer's account

Arup’s account of its work on Nottingham Contemporary art gallery by Caruso St John architects, photography by Helene Binet

Click here to read the building study by Kieran Long
Click here to read the architects’ account by Adam Caruso

Background

Nottingham Contemporary is a high profile, publically funded project creating the largest single gallery space in the East Midlands, and one of the most impressive contemporary arts spaces in the UK. It is scheduled to open to the public 13 November 2009.

Arup has been making a contribution to the city of Nottingham for over four decades, shaping many projects, particularly landmark developments focused around regeneration and sustainability. For this project Arup provided all engineering services including Structure, MEP, Civils, Geotechnics and specialist services from teams based both in Nottingham and London.

The building has a total floor area of over 3000m2 comprising a mix of flexible arts spaces and amenities including: four art galleries, a double-height performance space accommodating up to 200 people, café bar and offices.

The site in the centre of Nottingham conferred multiple constraints on the design of the building: 

  • Its triangular shape and footprint led to an arrangement of the space over four storeys,
  • The steeply sloping site led to three floors being underground.
  • The unearthing of a listed ancient cave monument, unknown caves, ditches, wells and pits; major city utilities, and abandoned historic railway infrastructure meant that this was an extremely challenging site to develop.

De-Risking the Site:

A long history of occupation extending back to the Anglo-Saxon period, and a steeply sloping topography meant that at the project’s inception, a major programme of site investigations was required to define an Enabling Works contract that would ‘de-risk’ the site in preparation for the main construction work.

The site had remained undeveloped largely due to the fact that access was heavily constrained;to enter the site from its lowest point at the south, long abandoned railway structures had to be demolished, including a disused railway tunnel and its associated cutting.  

The site falls as much as 13m from North to South and is enclosed to the East and West by up to 13m high existing retaining walls which support busy roads, car parks and buildings. 

The Enabling Works operation was so complex that some contractors refused to tender. To assist the bidders, Arup developed an indicative phasing approach early into the project; which was refined following archaeological investigation.

Archaeology

Below the surface, Arup were designing for multiple known and unknown challenges; the Broadmarsh Caves, an English Heritage Scheduled Ancient Monument and visitor attraction, were known to extend beneath the western edge of the site.  There was significant potential for discovery of additional unidentified caves and medieval archaeology. Nottingham has a rich heritage of caves cut into its underlying sandstone throughout its occupied history, and variously used as cellars, dwellings, and air-raid shelters.   

In addition to underground structures, the site hosts major utility infrastructure from which large areas of the city of Nottingham receive power, district heating and drainage. 

Arup staged archaeological investigations, and topographic surveys of the site and the underlying labyrinth of caves. Previously unrecorded caves were discovered and registered during the project.

Enabling Works

During the Enabling Works Arup led continuous and extensive negotiations with third parties and key stakeholders. Discussions took place early on in the project with English Heritage in order to ensure that the development would not adversely affect the Broadmarsh Caves.  Arup worked with the contractor to ensure that the caves remained open to the public throughout the development. The sub-basement excavation for the development was as close as 2m from these caves.

Below ground works also included:

  • The diversion of 2 500mm diameter district hot water heating pipes serving central Nottingham.  A new route for these pipes was integrated with the foundations for the new building and incorporated beneath the sub-basement floor slab.
  • The redesign and diversion of a major Victorian combined sewer including the protection of a sensitive Victorian oval brick sewer which placed restrictions on ground movements that limited construction techniques.
  • A major high pressure water diversion feeding the Broadmarsh Shopping Centre.
  • Diversions of highway drainage.
  • Diversions of medium voltage and mains electricity cabling.
  • Construction of contiguous piled walls to the Eastern and parts of the Western site boundaries formed a 13m deep basement extending below the foundations of the existing retaining walls.

Structure:

It was the intention from an early stage to form much of the structure of Nottingham Contemporary from exposed reinforced concrete, consistent with a building where the distinction between above ground and below ground accommodation is often ambiguous. The architectural aspiration was to evoke a ‘found space’ or warehouse context appropriate for contemporary art. Lace patterns are set in to the pre-cast concrete cladding in reference to Nottingham’s history of lace manufacture.

The challenge throughout the design was to resolve the technical obstacles posed by the site and the non-repetitive geometry of the architecture in a manner consistent with the architect’s vision for the building.

The finely-tuned co-ordination of structure, services, and architecture was a key part of the design process. Despite the heavy servicing required by the gallery, there were very few hidden spaces in the public areas from where services could be run. A case in point are the 1.6 metre deep concrete beams spanning over the performance space, arranged to generate the desired architectural rhythm, which are required to support heavy artworks located in the gallery space above, while at the same time accommodating holes up to 1600 x 600mm for service penetrations.

To avoid disturbing the Broadmarsh caves, which are open to the public and are a Scheduled Ancient Monument, it was necessary to design the South West corner of the building to span 40m over the caves. In a further example of the close co-ordination of structure and architecture, the transfer structure is unobtrusively integrated into the exposed walls of the building and café terrace.

The roof structure above the main entrance level is framed in steel as a more economical alternative to long-spanning concrete. The extent and close spacing of the roof lights required an unusually densely-framed beam layout, which had to be precisely co-ordinated to fit between the sculpted roof light coffers. At the same time, the coffers allowed little of the diaphragm action or bracing conventionally used to stabilise roof structures. Strips of concrete slab are strategically located around the roof to deal with these stability forces in a way that allowed full realisation of the desired daylighting strategy for the galleries.

The support of the cladding was another central design challenge. The sheer weight of the precast cladding units (up to 8 tonnes each), combined with their position outboard of the structure, means that particularly large forces are generated, which need to be carried by the structure. Arup developed a strategy in conjunction with Caruso St John for the locations and types of support to be provided on each façade of the building. Recognising this issue early in the design process enabled the structure and façade designs to then be developed in parallel.

Environmental Services:

Principle challenges for the environmental services were:

  • Taking best advantage of natural light and natural ventilation for a building that by virtue of its steeply sloping site is largely buried below ground.
  • Matching environmental systems to the varying demands of the mix of uses: from close environmental control for the protection of valuable art works, to large ventilation and heat loads of a performing arts spaces, to providing simpler systems for the offices and amenities.
  • Rather than a one-size-fits-all approach common in large gallery buildings, the air-conditioning design provides adaptable gallery systems which give staff the flexibility to simultaneously control a range of environmental conditions in different exhibit areas.  In this way, the costly provision of operating a close control art preservation environment can be restricted to certain galleries at certain times (depending on the exhibit), while the rest of the galleries can operate normally and more cost effectively.
  • The architectural character of the internal spaces combines expressed structural and building services elements, requiring an unusually precise coordination between space planning, engineering and finishes.

Primary zoning was adopted within the preliminary space planning of the art spaces. The development can be effectively be split into two ‘zones’.

Upper level (Ground) art spaces, providing a ‘natural home’ for visual arts:

  • Natural light welcome as an illuminant for art and as an energy efficient form of lighting. Extensive use of coffered skylights.
  • Close control of temperature and humidity sometimes needed to meet the requirements of loan agreement paintings, but not always for the whole floor.
  • Two zones of control were identified, a south zone where close humidity control is more likely, and a north zone where it is possible but may be deployed less often.

Lower Level art spaces, providing a ‘natural home’ for performing arts

  • Effectively ‘black box’ space – below ground and protected from climatic, acoustic and visual intrusion form the outside.
  • Ventilated to provide fresh air and some cooling to performers and spectators, but with no provision for close control of humidity.
  • A partially passive climate control using the mass of the exposed concrete structure to act as a ‘thermal flywheel’ and limit temperature drift at times of high occupancy.

The flexible nature of the systems does not limit particular works to certain floors: visual art including paintings can be shown on the lower level, equally the upper level art spaces can be used for performing arts.

Sustainability

The design team took a holistic approach to the energy efficiency and sustainability of the project; assessing the building form, fabric and design, how it relates to its site, plant efficiencies, renewable technologies, and costs.

Key sustainable elements include:

  • Pre-cast concrete facades and exposed concrete interior finishes provide thermal mass heat sinks to reduce peaks in daytime heating and cooling loads.
  • The thick perimeter walls provide integral shading to the set-back glazing in areas around the perimeter.
  • High performance double glazing has been incorporated in the façade and roof to limit the solar gains in summer and heat loss in winter, without jeopardising the access to natural light.
  • The cliff acts as an additional thermal buffer in the winter which reduces the heating energy required.
  • Natural ventilation is used in the offices, education rooms and public spaces except where a more controlled environment is needed for art conservation or performance.
  • Optimal use of natural light at the main entrance (Ground) level to reduce the requirement for electric lighting.
  • There is a section of green roofing which provides good natural insulation and reduces rainwater runoff.
  • The systems have been designed to incorporate energy efficient components for example all the air conditioning systems incorporate heat recovery
  • Fresh air ventilation rates controlled by CO2 sensors for major spaces which will take account of the large wings inoccupancy between public viewing and set-up.
  • A sophisticated building management system is used to control the mechanical systems, which will optimise the heating and cooling energy used. It will also monitor the systems and as a result will be able to inform the users when energy wasting leaks may have occurred and help to facilitate a timely repair.
  • The building’s primary heat source is the Nottingham district heating system which is predominantly fuelled by municipal waste and offers a green energy source for the building.

Lighting:

The Ground level galleries at the top of the building benefit from generous daylight levels for most of the year from the coffered skylights within the roof.  The glazing in these skylights incorporates a diffusing laminate that prevent sun patching within the galleries, and also filters out ultra-violet radiation. Daylight levels vary significantly in the gallery spaces depending on the sky conditions and time of year. A system of manually deployed blackout covers are provided so that reduced light levels can be created.  These covers can be clipped into place externally to cover the roof lights when required.

Daylight in these galleries is supplemented by fluorescent luminaires positioned in the gaps between the plywood coffers. These fixtures are dimmed according to exterior lighting conditions as sensed by a daylight sensor in each gallery. 

The art spaces are also provided with a flexible system for the highlighting of individual works:  in the Ground level galleries this is achieved through the provision of hidden lengths of mains voltage track recessed between the plywood coffers, into which wall-washing or spotlighting fixtures can be added.

A dimmed fluorescent “house lighting” system is provided in the basement performance space. This is designed to be controlled in conjunction with the dedicated theatrical lighting system or independently for special art exhibition events, seminars or lectures. Theatre lighting, audio and machinery power cables are distributed at high level and within the floor to meet the technical needs of a wide range of stage productions, without becoming visually intrusive.

Conclusion:

In retrospect, Nottingham Contemporary is an elegant, high quality response to what was an immensely challenging brief. The building responds purposefully and successfully to the topography of the site.

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