Beton House, Sheffield

Phase three of Park Hill regeneration offers a masterclass in reusing structures

Few buildings provide as valuable a template for the retrofit of existing concrete structures as the 1960s Park Hill estate in Sheffield. This is Europe’s largest listed building, and is being regenerated in a multi-phase programme by developer Urban Splash. In phase three, local practice Whittam Cox has taken one of the lower blocks of single and double-storey flats and converted it into a terrace of three-storey townhouses for student living.

This attempts to address one of the main failings of the estate: single-tenure housing rather than a mix of residents and uses. But the project is also notable for its strict strategy of retaining as many of the physical elements of the once-derelict structure as possible.

This process began with the original drawings, produced by Arup in the 1950s, which were used to develop a 3D BIM model of the existing building. From this, the team could calculate the tonnage of the frame and make a conservative estimate of its embodied carbon. This weighed in at 1,050,480 tonnes CO₂e, which will now continue to be useful for decades to come. In addition, the explicit strategy of retaining non-structural elements, such as floor screeds, concrete balconies, blockwork partitions and stairs, saved a further 577 tonnes CO₂e.

Material efficiency was also improved by the decision to leave much of the internal structure exposed. The original plaster had protected the boardmarked concrete beneath, and could be wet-scraped away and simply finished with an anti-carbonation coat. Elsewhere, more painstaking concrete restoration was needed. Many of the balustrade spindles, for example, showed severe spalling, but rather than removing them, the team managed to save 90% through careful repair work.

Throughout the project, a conservation-led approach has been taken, with the architects keen to express rather than conceal the repairs,” says Matt Borland, associate director at Whittam Cox. “We went through a lengthy process with the conservation officer to agree a colour for the patch repairs. The concrete is quite unique, with a brown tone from the aggregate mix that was used, and it varies a bit as well because of the way they cast it originally.

There were also a number of different textures – some where you could still see the wood grain from the board marking, and other that were really badly washed out.” The decision was taken to use a smooth repair mortar with a consistent colour throughout, so that repairs would be visible and read as part of the history of the building. All of the repaired concrete was finished with a clear, matt protective coating.

Cold bridges also proved a challenge – the estate having been designed before avoidance of thermal bridging was a consideration. Passivhaus modelling was used to work out how thermal improvements could be made. Insulated linings have been used as much as possible to create a break between the external and internal structure, helping to achieve a weighted U-value of 0.22W/m²K.

The as-built operational emissions of the townhouses have been measured at 33kgCO₂e/m², but Whittam Cox expects this to improve and is continuing to monitor energy use on a meter-by-meter basis. The building is also all-electric – by replacing gas for heating and hot water, it will rely less and less on fossil fuels as the national grid switches over to renewable sources.