Mikhail Riches has taken a light-touch approach to the latest phase of the mammoth regeneration project, celebrating the original structure while updating it to modern standards
There is more than one way to revamp a brutalist icon. A decade ago, Hawkins\Brown and developer Urban Splash gave the derelict Park Hill estate a new identity and a vibrant facade of primary-toned sliding panels. Phase two, now nearing completion, follows that successful rebrand with a more understated approach. Architect Mikhail Riches has taken a huge eight-ten storey block, shaped like a five-sided horseshoe, in the middle of the grade II*-listed site and reconfigured it as 195 new homes and approximately 2,000m2 of offices, retail and cafes, with a more muted palette and a lighter touch to the original structure.
The infill brickwork has been retained, and cleaned with a fine aggregate-based jet wash to restore the two-storey bands of terracotta, light red and cream that demarcate the iconic “streets in the sky” access decks, of which Park Hill was the first built example. Colour – in 12 subdued tones – has been added to the balcony reveals rather than the main face of the building. “So when you look at it front on, you just see the brick. But as you turn the corner, the colour reveals itself,” says Alim Saleh, senior architect at Mikhail Riches.
The starting point for the architects was to pore over Arup’s original hand drawings for the scheme from the late 1950s. “We were able to obtain hundreds of them – everything from GAs [general arrangement drawings] to details to reinforcement, all setting out the concrete frame and structure,” says Saleh. “We had to scan them, blow them up and sometimes decipher what they meant. We also had to translate everything from feet and inches – which was a lengthy process. And that's what we then used to create our 3D BIM model.”
The drawings revealed a structure that was supremely efficient in terms of material use, but also showing many of the typical flaws of concrete buildings from its era. “Arup basically engineered it so well that there was no waste – the concrete was exactly what was needed and no more.” The slabs are extremely thin, varying between 127mm and 152mm. “In some areas, there wasn't enough rebar cover, by modern standards, so weathering and concrete spall had developed over the years.” There was further spalling on the balustrades and handrails, some of which had almost entirely broken away.
A more fundamental problem was the cold bridging inherent in the structure. The beams and slabs run through the apartments to the balconies and streets in the sky, with only a layer of asphalt covering the concrete decks. The streets also had low soffits, not only making them feel cramped and institutional, but giving the team very little space to work with. As much insulation as possible has been added while still maintaining a 2.2m floor-to-ceiling height, including linings to all of the decks, soffits and external beams and an upgraded 600mm floor zone inside the flats. Concrete balcony window upstands were replaced and the brick balcony reveals were coated with insulated render rather than paint. Passivhaus modelling software was then used to test thermal bridges.
Each flat has also been given a wet-pour resin stone entrance threshold, cast with patterns inspired by the original 1950s linoleum. There are 12 patterns, corresponding with the 12 coloured balcony reveals, which give a sense of identity back to the flats. This approach was prompted by the way that residents had adapted the flats over the years: “What we noticed when we first looked around the building was that people had started to paint their own balcony reveals. It allowed them to stand back from the building, look up and say, ‘Oh, that's my flat. The pink one.’”
The balustrades and handrails have been replaced wholesale with precast replicas, reduced in size slightly to leave a shadow gap to the concrete frame. And there’s a new in-situ concrete bin store, its plywood markings set out to follow the same board widths as the original columns and beams.
The main structural alterations to the building involved the removal of some party walls. The flats at Park Hill are configured as maisonettes, either going up or down from each street, but the smallest were just half a bay wide at the back, which was incompatible with modern space standards. “Where these units backed on to each other, we merged them into a large flat with a double-bay living space,” says Saleh. “Or we gave them back to an adjoining flat to make them more generous. But by doing that we’ve ended up with 36 different flat types – a lot more than we originally thought.”
At ground-floor level, a double-height entrance lobby has been created by removing the first-floor slab and sacrificing the residential space above. The perimeter columns have been reinforced and thickened, with rebar dowelled into the existing columns and new concrete cast flush against them, boardmarked to echo the original. Where the slab has been taken out, the newly exposed concrete edge has been hand-tooled: “It was about trying to leave a visible scarline and celebrating the history of the building,” says Saleh.
Elsewhere, concrete has been repaired where needed. This involved cutting out the damaged area and replacing the corroded reinforcement, before building up the repair mortar to the required depth. A few different methods were trialled on one of the estate buildings still awaiting regeneration to mimic the “rough and ready” texture of the finish, says Saleh. “The subcontractor looked at using a plastic float and then a very soft brush. But Historic England wanted it to feel much rougher and more in keeping with the existing frame, so we used thicker, coarser brushes.” A twist came when they looked again at the columns on phase two and realised that some had vertical joint marks from the timber shuttering, which were not evident on the trial building, where smoother plastic-coated formwork had been adopted. “They had some artistic licence, so tooled a line down the repair with a ruler to bring that joint back.”
The repairs were finished with a Keim anti-carbonation colour wash to blend in with the surrounding concrete. Even so, Mikhail Riches was keen for traces of the building’s former life to remain. Timber blocks embedded into the concrete, used for fixing skirtings, door frames and windows, have been exposed, as have electrical sockets and switches that were cast in the walls. The brickwork facades still show areas of dark carbon staining. “At first, we wanted to get them as clean as possible, but we couldn’t do that without damaging the integrity of the brick. And actually, seeing that staining on the brick, it tells us the story of its past. It’s not perfect but it’s part of its beauty.”