Park Hill Phase 2 by Mikhail Riches: less vibrancy, more subtlety
While the scheme still contains some three-bed units, usually at atypical, cranked knuckle points in the plan, it feels as though the demographic encouraged and expected here is more couples than families.
One can’t but help read a slightly bish-bash-bosh noughties optimism in the first phase compared with Mikhail Riches’ more subdued and subtle rework, slightly austerity-Britain
‘Where once brick infills progressed from brown to beige, now metal panels go from blood red to lime green. Park Hill’s been Tangoed. Pantoned. Urban Splashed.’
Source:Left: Keith Collie, right: Daniel Hopkinson
The project started with an analysis and survey of the existing structure – including full thermal modelling – although unhelpfully very few of the original construction drawings exist. It was one of Arup’s first concrete-framed buildings and has suffered the problems of many early concrete frames, with only 100mm-thick slabs in places, meaning water ingress has resulted in bad spalling to edges. ‘But it’s incredibly well detailed,’ says Riches, pointing to the drips cast into the underside of slabs. ‘These basically saved the building from being in a far worse condition.
In 2015 Urban Splash held a competition for Phase 2 of the project: 195 flats and 2,000m2 of commercial space. It gave the five shortlisted practices a flat in the derelict building and two weeks to demonstrate their ideas. The brief asked the architects to ‘spend as much time on the site, live and breathe it, wholeheartedly commit – can you do this?’
‘It’s also incredibly complex – more like a 3D jigsaw puzzle. That meant every corner has had to have a bespoke solution to the wet-cold frame. It would have been so much easier just to overclad it!’
More successfully, glazed slots with built-in shelves have been cut next to front doors, allowing better light and overlooking and also a chance to display objects as a marker personalising each entrance – a feature inspired by the corner display windows incorporated into the entrances of Phase 1.
The past decade has seen the focus on reducing embodied carbon shift the approach of retrofit to maximum retention of fabric. Indeed, the choice of Mikhail Riches – a practice known for its fabric-first, materials-based work – was perhaps itself reflective of this changed thinking. In the final round of the 2015 competition, when each shortlisted practice was given an empty flat to work with for the final interview, rather than attempting a temporary wasteful fit-out, the practice illustrated its concept simply and economically with drawn sketches on the room walls. Looking appropriately like 50s magazine illustrations, these incorporated patterns and cartoons from the fragments of remaining wallpaper into the design. ‘We felt from the beginning that they really understood the DNA of the block,’ says Latham.
Indeed, at Park Hill the access balconies were even named after those terraced streets they had replaced, with many residents rehoused next door to their previous neighbours. The maisonette units were grouped generally in clusters of four, with adjacent front doors and sharing back-to-back H-shaped service riser cores. Two units have their main floor below deck level and two above, while all run through the width of the block enjoying good cross-ventilation. Facilities for the whole complex, meanwhile, included a nursery and primary school, shopping centre, four pubs and even apparently a mortuary.
We are also working with low existing ceiling heights: floor-to-floor dimensions are 2,515mm (these would be at least 3,100mm in a modern building) but to achieve the best results thermally within the tight parameters we have added insulation to bring ceiling heights to 2,215mm.
Repair mortar and an anti-carbonation coating was applied to all exposed concrete elements. The aim of this coating was to provide a barrier to mitigate further carbonation and extend the design life of the superstructure frame.
But the completion of Phase 1 undoubtedly remains a signature model for the reimagining and rehabilitation of Modernist estates, both as places to live and in the public imagination. It was shortlisted for the 2013 Stirling Prize at a time when the demolition of other prominent examples, such as London’s Heygate Estate, was gathering pace.
The scope of other future elements remains under question. The S1 artist-led gallery space and studios planned for Phase 4, won in competition by Carmody Groarke in 2017, is still seeking more funding.
Civic Engineers acted as civil and structural engineer on Park Hill Phase 2 for Urban Splash. Having provided the same service and support on Phase 1 (2007-2011) and Phase 3 (2017-2020), Phase 2 saw our role evolve as we designed a retentionist repair strategy for the existing concrete frame. The principal design aims of this were:
Percentage of floor area with daylight factor >2% Not measured | Percentage of floor area with daylight factor >5% Not measured | On-site energy generation 0% | Heating and hot water load 91 kWh/m2/yr (estimated) | Total energy load 157 kWh/m2/yr (estimated) | Carbon emissions (all) 57 kgCO2/m2 (estimated) | Annual mains water consumption Not supplied | Average airtightness at 50Pa 4m3/hr/m2 (actual tested average) | Overall thermal bridging heat transfer coefficient (Y-value) 0.16 W/m2K | Overall area-weighted U-value 0.42 W/m2K (including thermal bridges) | Predicted embodied / whole-life carbon 360 kgCO2eq/m2 (post-retrofit) | Predicted design life in years 60 years (estimated)
Up at deck level, the width of the ‘streets-in-the-sky’ has been preserved. This is in contrast to Phase 1, where entrances were built out into the access decks, with alcoves lined in noughties-style timber, forming deep warm thresholds to each group of four flats. Mikhail Riches has opted for a subtler delineation of threshold, with the entrances to two of each foursome being slightly recessed. To this has been added a slightly tongue-in-cheek decorative ‘mat’ delineated as a pattern within the black resin deck of the access balcony. These were inspired by the ad-hoc mats of patterned lino that earlier residents had glued to the concrete deck in an attempt to individualise and humanise their front doors. It’s not totally successful, looking a bit crude and overthought. Indeed the black resin flooring, which is acoustically dampened on rubber crumb, was chosen to match the look of the original street-like asphalt but feels as if it could have been lighter. It reduces light-levels in the low deep deck spaces and is unforgiving in showing up dirt and litter.
It was one of the earliest and most complete manifestations of the ‘streets-in-the-sky’ concept first mooted by the Smithsons in their 1952 Golden Lane Estate competition entry – itself channelling Le Corbusier’s original Unité in Marseilles. The basic model was of mega-blocks or estates functioning as self-contained neighbourhoods, with dwellings accessed off supposedly street-like pedestrian walkways, separated from vehicular traffic.
Completed in 1961 by Sheffield City Council, Park Hill is a Grade II*-listed Brutalist housing scheme, containing 1,000 homes, making it Europe’s largest listed structure. Urban Splash took on its redevelopment and Phases 1, 2 and 3 are now complete.
Mikhail Riches’ sensitive picking up on and referencing of clues offered by the existing fabric has been a feature of its nuanced approach throughout the project.
This report was crucial for our performance specification and repair strategy which included removing areas of defective concrete, including cleaning and removal of corroded reinforcement. Where corrosion of exposed reinforcement was significant, bars were locally cut out and replaced with new welded reinforcing bar primed for application of repair mortar.
Planned by Sheffield Council’s architecture team under city architect JL Womersley, Park Hill replaced an area of back-to-back terrace streets which had been condemned as slums and had gained a reputation for gangland crime, earning it the moniker Little Chicago. When completed, the scheme was thought to be the longest building in the UK with its series of cranked blocks all sharing the same roof datum and linked by a series of access balconies. These cleverly use the steeply sloping site, being accessed at ground level at one end while ending several storeys up at the other where the land drops away. This, together with their generous width, famously enabled milk-floats to drive along them, delivering to individual doorsteps.
The works to the concrete frame created a robust and durable exterior allowing safe reoccupation of the structure.
Dan Podesta, associate, Civic Engineers
Start on site January 2019 | Completion August 2022 | Gross internal floor area 12,750m2 (GIA residential area), 2,000m2 (GIA commercial area) | Construction cost Undisclosed | Architect Mikhail Riches | Client Urban Splash | Structural Engineer Civic Engineers | M&E consultant Beechfield Consulting Engineers | Quantity surveyor Broadfield Project Management | Project manager Broadfield Project Management | Principal designer Rawlings | CDM co-ordinator Rawlings | Approved building inspector Salus Approved Inspectors | Acoustics Sandy Brown | Fire CHPK Fire Engineering | Sustainability / thermal Greengauge Building Energy Consultant | Landscape Austin-Smith:Lord | Main contractor Urban Splash Construct | CAD software used ArchiCAD | Predicted annual CO2 emissions (operational) 20 kgCO2/m2 (post-retrofit)
The only major demolition of the frame has been around the entrance areas, where new double-height lobbies have been created through the removal of flat units. The treatment of these lobbies is much rawer than in Phase 1. There, elements like a shiny sculptural stainless-steel stair were inserted; here, lifts and stairs remain strictly orthogonal and utilitarian, with existing concrete walls left showing all their history, including the cast-in timber chocks used to attach skirtings in the lost flat units.
That initial phase was the first of five mapped out by HawkinsBrown and Studio Egret West in a masterplan for Urban Splash in 2007. Now Phase 2 of 195 units has been completed by Mikhail Riches. The decade’s delay is indicative of the backwash in the property market caused by the financial crash, which saw both Urban Splash in difficulties and the withdrawal of central government funding, which had enabled 40 per cent of the Phase 1 units to be subsidised for social rent. As such, Phase 2 consists of just affordable and market-price housing, although Latham says the ambition remains to meet the original target of 20 per cent social rent across the whole scheme. The mix of the development has changed in other ways too, with Phase 3 developed by Alumno Developments as student flats in a retrofit completed by Whittam Cox Architects last year.
Park Hill is an exposed concrete frame building. Its Grade II*-listed status means that overcladding the concrete, which acts as a massive cold bridge, was not an option; we needed to insulate both sides of the concrete in each room.
In any case, the steer from English Heritage – after the more billboard nature of Phase 1 – was that this phase should retain more of the original fabric in light of the estate’s listing. Another factor was the knowledge that, whereas the enormous amount of spoil from Phase 1 was reused to form the landscaping, any demolished fabric from later phases would have to be expensively removed from the site.
Internally, the tight layout of each flat has been eased by converting most three-bed units to two-bed with an added en-suite. The sense of openness has also been increased by removing walls between stairs and landings. The wall finishes wrapping around the stairs are nicely left as raw concrete – it being far enough away from the external envelope for insulation to offer only limited thermal benefit.
Gobsmackingly, it was just one of four huge estates – and not even the largest – planned and built in a ring around Sheffield by Womersley’s team. However, as with many other large Modernist estates in the UK and against a background of deindustrialisation and rising unemployment in the 1970s and 80s, all four estates suffered from lack of maintenance and antisocial behaviour. By the following decade, the other three had been totally or partially demolished. It’s a fate Park Hill might have suffered too but for its Grade II*-listing in 1998, in recognition of its importance as a fully realised version of ‘streets-in the-sky’ and its inspired use of its hillside site.
The design of the repairs was launched with a concrete condition survey of the structural frame to confirm its quality, identify defects and specify remediation works.
This was Rory Olcayto in the AJ in 2013 describing the vivid visual hit of anodised aluminium panels used by HawkinsBrown and Studio Egret West in the first phase of Park Hill’s retrofit for Urban Splash.
The brickwork has been lightly cleaned externally and insulated internally. New windows are pushed back to the thermal line with pressed aluminium reveals creating depth to the façade, providing some solar shading while giving the brick an equivalent treatment to Phase 1’s brightly coloured panels.
Alim Saleh, senior architect, Mikhail Riches
‘We wanted it to be visibly transformed,’ said Urban Splash development manager Mark Latham at the time of this initial zingy regeneration of 260 of the almost 1,000 flats in the Modernist estate, originally completed in 1961 to designs by Ivor Smith and Jack Lynn, which sits prominently on a hilltop to the east of Sheffield’s city centre. ‘It was important for making people realise what it could be.’