Downland Gridshell – Project History and Design Brief

Introduction

The Downland Gridshell is an innovative modern timber gridshell structure intended to become the national centre for the conservation and study of traditional timber-frame buildings.

The gridshell, which uses new techniques, researched especially for this project, houses the Museum’s collections in an open access store. The project has attracted considerable interest, and the process of construction has been accessible to visitors.

Four front-line firms of architects were interviewed to design the Museum’s new Building Conservation Centre in 1996. They were required to propose an innovative building that would respond to the physical demands of the Museum and the sense of foresight held by its directorship. Rather than mirror the past, the new structure was to celebrate the special environment of the Weald and Downland region and serve as an exemplar structure for modern rural buildings.

Edward Cullinan Architects was appointed, working with Buro Happold engineers, Alex Sayer quantity surveyors and The Green Oak Carpentry Company Ltd. The Museum’s Directors have actively participated in and supported the approach that led to this unusual and unprecedented project.

The Weald & Downland Open Air Museum, a leading international centre for historic buildings, attracts 140,000 visitors a year. For over 30 years it has rescued and preserved threatened 15th – 19thth century buildings and artefacts that record the history of traditional rural life in the surrounding region of Kent, Sussex, Surrey and eastern Hampshire.

The Museum’s restoration and erection of original buildings provides visitors with a unique three-dimensional textbook of over 500 years of building materials and methods. The 50-acre open air site situated in the South Downs at Singleton, near Chichester, comprises more than 45 buildings and a major collection of artefacts and specialist library.

The new purpose-built Conservation Centre and Store will, for the first time, allow the Museum to make its research, conservation and restoration programme for houses, workshops, town and farm buildings accessible for viewing to the general public. The Museum’s stored collection of artefacts, relating to buildings, building trades and materials and rural life, will be brought onto the site for the first time, giving the artefacts a greater level of security, environmental stability and visibility.

The new building is intended to be a national facility for the study and practice of building conservation, especially the timber-framing tradition of England. The Museum already has an enviable reputation as a centre of excellence in building conservation training and for its extensive programme of traditional rural trades, crafts and skills courses. The building incorporates three integrated workshops for carpentry, building, plumbing, roofing and wheelwrighting conservation and restoration, which will bring these key crafts into the public arena. A classroom will allow practical workshops for up to 12 people at a time to learn traditional crafts and construction skills no longer taught in the modern building industry, but desperately needed by the conservation sector.

The environmentally controlled artefacts store will ensure the long term care and safety of the Museum’s collection, Designated by the Government for its international importance last year. Bringing the collection onto the Museum site will save at least £30,000 a year in off-site storage.

The new building has already generated new research and will continue to stimulate new ideas and solutions. The construction process of the timber gridshell was also a once-only opportunity for educational activity. Visitors were able to watch the gridshell take shape from a safe viewpoint.

The “Downland Gridshell” is a testament to architectural and building techniques of the early 21st century, as the Museum’s existing buildings are to their own time, and at the same time complement and extend the collection and work of this leading Museum.

Architects original views of the project

Cross section

Cross section

North elevation

North elevation

Plan

Plan

Project Overview

The Open Access Building Conservation Workshop, Demonstration Area and Museum Store is be housed in an innovative greenwood structure designed by Edward Cullinan Architects with Buro Happold Engineers. Practical in operation and innovative in design, this unique building is both visually elegant and holistic in its environmental impact. The conservation centre reflects the theme of the craft of timber using traditional materials, in a design philosophy that is entirely consistent with the Museum’s objectives.

Building the conservation centre for the Weald & Downland Open Air Museum has explored new techniques in greenwood timber construction. The undulating organic form of what has become affectionately known as the ‘Downland Gridshell’, seems to reflect the rolling South Downs countryside. The challenging site, in an elevated position within an area of outstanding natural beauty on the South Downs, called for a high quality structure, sensitive to the local environment. Given the contrasting uses of the building, the decision was made to employ a loosely clad clear-span timber gridshell workshop, set upon a sealed and sunken archive space of earth protected masonry.

The efficient and flexible structural form provided new potential for locally available materials and skills. The organic form is due primarily to the stiffness requirement for the shape of a gridshell, composed of a series of continuous curves. The complete form is a triple bulb hour glass, 12-15m wide, with 5m deep open ends to allow access to the building’s interior. Although two storeys high, from the outside the 1800 m2 building appears to be a single storey structure.

Internally the building is a single cell space enclosing two sealed workshop units. The gridshell is clad with a loose system of hanging plates of hardwood and glazing, while the difficult to drain upper pitches of the building vault is clad in a curving ribbon of watertight monolithic roof.

The two levels are separated by a built up floor structure of laminated beams on a central row of glu-laminated columns supporting a sealed and insulated industrial grade timber plank deck.

In contrast to the airy, loose construction of the upper floor, the lower level is sunk into the surrounding chalk site. Mostly buried archival areas are sealed and atmospherically controlled to maintain an overall 18-25C temperature to allow for long term processing, storage and display of the Museum’s archival stock. Within the main shell smaller areas provide their own macro environments for more sensitive materials. To reduce loads on water and power supplies the building and site systems take advantage of natural features such as earth mass, found by digging into the ground, and rainwater collection.

The building makes use of materially and energy efficient systems.

Structural and mechanical systems used get the most out of relatively small amounts of resources. An example of this is that the gridshell covering the entire workshop is constructed from timber. The material has been tested for strength and quality and applied in a way which makes effective use of computer supported engineering techniques.

Environmental issues

The building will run on minimal supplies of energy. Heat and power will be used as necessary and only in rooms where required. Where people will be exerting themselves physically, the building will not provide unnecessary heat. Controlled natural light will make artificial lighting during daylight hours redundant. Direct solar collection will pre-heat water, to be pumped through an underfloor heating system in the lower level. This floor heating strategy enables a direct thermal connection between the floor slab and the ground which will act as a heat sink, keeping the archival spaces thermally stable throughout the year. The only insulation materials used are at the upper zones of the external walls and the encasing ground.

Carpentry Specialists

This building presented exciting challenges to The Green Oak Carpentry Company team. In many ways this is a ‘carpenter’s building’ incorporating as it does a wide range of carpentry disciplines and structural techniques, such as solid oak framing like that on display at the Museum, large curved ‘glulam’ beams made up from thin planks, bent and glued together, and the gridshell itself, which might be likened to a giant ‘wooden basket’ moulded into a triple domed structure.

Also unique is the green jointing of the gridshell laths from freshly sawn oak. This means that the timber is more supple and therefore more easily formed. Glue technology has moved forward to a stage where this is now possible on a structure of this type.

Of interest is the use of locally grown Western Red Cedar boarding fixed vertically in tiers up the building, and which resemble the articulation of medieval armour.

The construction of the ‘ribbon roof’ that undulates over the entire length of the structure, is perhaps more akin to boat building than conventional roof construction as we know it.

The design process for the building has also been unusual in that from an early stage, the carpenters sat around the table with the architects and engineers to design the detail of the building. Putting all this together we have a building that is unique and innovative, both in its conception, engineering and its carpentry. It is our belief that the results speak for themselves.

The Design Team

Architects: Edward Cullinan Architects

Team: Edward Cullinan, Steve Johnson, Robin Nicholson, John Romer Edward

Edward Cullinan Architects’ 33 years of experience includes urban and rural master planning as well as the design and construction of a wide range of building types. The practice has remained deliberately broad based and non-specialised. Its interest is in the careful, inventive design and detailing of buildings that are responsive to their surroundings, useful to the occupants and good to be in. The practice has frequently built successful modern buildings in sensitive, historic surroundings and within the setting of much loved, often listed structures and is skilled at working with clients to anticipate their future needs, developing brief and design together. A commitment to the practice of the art of architecture has resulted in the practice’s work being published, exhibited and discussed extensively, both here and abroad. The practice has received many awards for its work, and and several of its members teach design at university level, both here and abroad.

Engineers: Buro Happold

Team: Michael Dickson, Richard Harris, James Rowe, Peter Moseley

Buro Happold is a multi-disciplinary international practice of consulting engineers establishedin1976 offering civil and structural engineering, mechanical and electrical engineering, quantity surveying, building services and environmental engineering, infrastructure and traffic engineering, geotechnical engineering, facade engineering, fire engineering, Computational Fluid Dynamics analysis, access consultancy, project management, urban design and a range of specialist CAD services.

Project Manager and Quantity Surveyor: Boxall Sayer Ltd

Team: Clive Sayer, David Foster, Paul Comins

Founded in 1946 Boxall Sayer Ltd offers a full range of Quantity Surveying and Construction Cost Management services. The practice also offers Planning Supervisor Services under the Construction (Design and Management) Regulations 1994 and a range of advice on the new procedures involved.

Projects covered include new-build, refurbishment and planned maintenance in all sectors of the construction industry. Those in-hand range from maintenance and improvement schemes costing a few thousand to major redevelopments costing millions and include sports & leisure centres, educational buildings, heritage schemes, retail schemes, industrial and office complexes and residential sites.

Main Contractor: E.A. Chiverton Ltd

Team: Mike Wigmore, Chris Silverson

Founded in 1945 the firm offers a complete range of construction services mainly within West Sussex and Hampshire.

Recent projects include a Lottery Funded sports complex for Bognor Regis College £2.9 M, a new Health and Fitness Suite for the Westgate Centre, Chichester for £1.6 M and three new primary schools for West Sussex County Council each with a value of c£900,000.

The firm has experience of major works in Public and Community buildings, Commercial, Historic Building Refurbishment, Sports Facilities, Schools, Surgeries and Housing, as well as maintaining a general works department carrying out smaller projects.

Specialist Scaffolding Contractor: PERI

Team: Carl Heathcote, Jurgen Kuerth, Howard Ball

PERI was founded in Germany in 1969 and is still run and operated by the founder.
PERI designs manufactures and supplies worldwide innovative formwork and scaffolding systems for sale or hire to the construction industry. The Downland Gridshell has given PERI the opportunity to demonstrate the benefits of both formwork and scaffolding systems in one construction.

Recent projects undertaken include the refurbishment of the Harrods Depository at Hammersmith, the German and Japanese Pavilions at the Hanover Expo Fair, window replacement contracts in London………

Carpentry Specialists: Green Oak Carpentry Company Ltd

Team: Andrew Holloway, Steve Corbett

Green Oak Carpentry Company Ltd are specialists in the design and fabrication of new oak timber framed structures, and the restoration of old timber buildings. Projects include design and construction of ‘barn’ houses, conservatories, pool buildings, garden structures and so on. Recently the company constructed a bridge over Grand Union Canal with a single span of over 17 metres for Ealing Borough Council.

The company is committed to the development of new and exciting timber structures, arising out a good understanding of historic timber buildings. Over the years we have established an excellent reputation for craftsmanship and innovation. Clients include The National Trust, The Royal Parks, The Weald & Downland Open Air Museum and many private clients.