The Hepworth Wakefield

The new Hepworth Wakefield gallery is the focal point of regeneration on the River Calder waterfront, formerly the site of a huddle of low mill buildings. It houses a collection of sculpture by local-born artist Barbara Hepworth alongside the works of other prominent artists, and is one of the largest art galleries yet built outside London.

As a response to its environment, the building was conceived as a group of ten linked blocks of varying sizes, and is expressed in pigmented self-compacting concrete. The addition of pigment was untried in this country and required the development of dedicated pour techniques to get the meticulous mirror finish specified. This route to achieving the design proved highly cost effective compared with precast options, as well as advancing UK industry knowledge in aesthetic concrete techniques.

The two-storey building houses a learning suite, café, lecture theatre and ancillary facilities on the ground floor, with ten gallery spaces above. The various skew roofs of the airy gallery spaces, up to 13m high, enable generous clerestory glazing as part of the natural lighting strategy.

The river elevation sits directly above the water. Below, river water is directed through the line of an old mill race at basement level to provide cooling – part of a sustainable and highly integrated building services agenda designed to achieve a ‘very good’ BREEAM rating. A detailed anti-clash 3D model helped optimise structure and services integration throughout. The mass of the building is part of the flood protection strategy for the waterfront area.

The structure is founded on a 400mm raft slab on CFA piles. Floor spans are constructed in either flab slab, T-beam slab or post-tensioned concrete, depending on column spacing. The gallery floors are topped with a monolithic 20mm screed, with two-way movement joints at the perimeters. Steel roof trusses support precast concrete planks.

Our engineers and consultants worked on all aspects of the gallery complex, including the new access bridge across the river for cyclists and pedestrians.

facade engineering

As a response to its environment, the new Hepworth Wakefield gallery was conceived as a group of ten linked blocks of varying sizes, reminiscent of the huddle of low mill buildings that once characterised the riverside site. The two-storey building houses a learning suite, café, lecture theatre and ancillary facilities on the ground floor, with ten gallery spaces above. Local-born sculptor Barbara Hepworth is shown along with the work of other prominent artists.

Our façade engineers started with extensive research into suitable materials to realise the architect's vision of a high quality mirror finish to the building. Polished precast concrete panelling using a specialised aggregate was the initial idea. However, following a budget review and value engineering, an in situ concrete structural solution was chosen. To achieve the desired effect, pigmented self-compacting concrete has been used.

The addition of pigment to to self-compacting concrete was untried in this country and required the development of dedicated pour techniques and aggregated mix design to get the meticulous finish specified. After intensive testing, limestone fines were chosen to replace PFA, and a pour technique that ensured even colouring were used, resulting in an integral structural and facade solution.

The detailing of the façade required cold bridge analysis to be carried out. Risk analysis highlighted that the building's waterside location meant condensation could potentially build up in the façade, causing mildew. Flixo software was used for iso-thermal analysis to assist with the detailing and minimise the risk of condensation, and also to reduce heating costs.

fire & safety

Our fire consultants work to make designs fire-safe, rather than allow generic fire regulations to dictate design. This emphasis is never more relevant than in dealing with landmark structures such as architect David Chipperfield's new gallery building on the River Calder. Here, we represented the project in tripartite negotiations with the insurers, local Building Control and the Museums, Libraries & Archives Council (MLA) to agree basic fire safety standards that integrate effectively with the building's design.

The objective of the fire strategy is to enable the openness of the building desired by the architect and client — and the use of materials — while ensuring safety for visitors and the exhibits.

A key component are the 'virtual' fire compartments: horizontal and vertical compartments achieved using the inherent performance of the architect's design. These compartments create the opportunity for horizontal movement to a place of safety, which assures safety for large numbers of people and allows the gallery to respond flexibly to the needs of disabled persons. It also enables an effective salvage strategy, thus integrating the means of escape and fire-fighting strategy with the security strategy.

We minimised the number of fire dampers required in the building through close coordination with the design of the ventilation system and capitalising on the inherent performance of the ductwork.

geotechnical engineering

The early involvement of our geotechnical engineers at The Hepworth Wakefield provided the integrated engineering and design team with a comprehensive site model for the new gallery on its riverside site. Historically, this site had been raised to compensate for a 2m drop in the River Calder. The resulting made ground varies between 2m-3m in depth and is in reasonable condition despite a degree of contamination from former industrial use.

We suggested options for the construction of foundations and a basement where the removal of contaminated materials from site is not desirable. Our engineering designs incorporate the need for water resistance and protection measures to cope with carbon dioxide gas that may result from the decomposition of organic materials in the made ground.

Geotechnical testing and analysis also informed the design of the foundations. End bearing piles sunk through made material into rock were tested for performance under tension caused by hydrostatic uplift. The final in situ concrete two-storey structure, with single-level basement, is founded on a 400mm raft slab on CFA piles.