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.
The works to the concrete frame created a robust and durable exterior allowing safe reoccupation of the structure.
Dan Podesta, associate, Civic Engineers
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.
Riches says that dealing with the base of the blocks was a key issue as ‘there’s no single ground floor’ due to the sloping site. They are in part populated logically here with three bay-wide accessible flat units and ‘townhouses’ with their own separate entrances, semi-private patios and a shared garden. The majority though are divided up into 1,850m2 of mixed-use work and commercial space. One unit with a large west-facing terrace has been earmarked for a restaurant, indicating how, as more phases complete and people move in, more businesses can viably be based here.
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.
Internally, rooms have been lined like ‘insulated boxes’– with insulation added to the cavity wall brick panels, windows moved back into thermal line and balcony flank walls and the soffits of living spaces all lined in insulation. The latter, while aiding with acoustic separation and providing a concealed service zone, also results in an unfortunate squeezing of head height, given the already low floor-to-floor dimensions of 2.515m, to just 2.215m.
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.
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.
Thermal imaging of the Phase 1 façade showed that the concrete frame on the balcony cheeks was the most thermally leaky element. This informed our response to insulating the exterior reveals of the building, expressed as coloured render panels. The building was thermally modelled by Greengage, which advised where insulation is best placed and which thicknesses will optimise its performance.
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.
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.
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.
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
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.
We spent two weeks looking at the building, studying it and learning from Phase 1. We noticed the remnants of lives lived there, the traces of inhabitation and how residents had made their flats homes. Some had painted their balcony cheeks different colours, all had laid patterned linoleum on their doorsteps. We won the competition with our proposal: to faithfully restore the building keeping as much of the existing fabric as possible, upgrading it thermally and acoustically, and giving each flat its own identity using patterned doormats and coloured balcony reveals.
‘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!’
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.
Source:Left: Keith Collie, right: Daniel Hopkinson
‘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.’
The challenge has been achieving this while working within the constraints of a very specific design (which is not as repetitive as it appears), and the size and layout of the existing flats, which do not meet modern standards and ways of living. We found that eliminating ‘problem’ bedsit flats allowed us to reconfigure the remaining existing flats and unlocked a new knock-through flat type, with fantastic double-width balconies. As a result, all the flats now have generous open plan living spaces, orientated to take advantage of the best views. This approach allows the retention of the external brick walls and window openings and the majority of party walls, which is very cost efficient and minimises construction waste.
Alim Saleh, senior architect, Mikhail Riches
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
The listing, while saving the building, threw up extra issues for retrofitting it and making it financially viable for a developer to take it on. Given this, it was agreed, after discussions with English Heritage, that for Phase 1, Urban Splash could strip the structure back to the frame and rebuild from there. The bright-hued ‘look-at-me’ transformation was the result, with the pinkish and buff brick infill panels replaced by powder-coated aluminium. In addition, the previous balance between window and solid wall was inverted, significantly increasing the proportion of glazing on the façade.
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.