Purcell had its work cut out creating new exhibition halls in an Edwardian courtyard and a new entrance in a listed facade – all of it reversible. Tom Brigden tells how the firm worked with planning and site constraints on the £12 million project
Give us an idea of the context
Manchester Museum occupies a series of linked buildings on Oxford Road, most notably the grade II* listed 1888 one by Alfred Waterhouse. It was a family affair. Son Paul did the adjacent Haworth building in 1912 and annexe a year later – both grade II. Grandson Michael built onto this in 1927, linking it to the 1908 dental school. There were ad hoc additions over time as routes in and through the museum were always problematic. In 2003 an Ian Simpson Associates extension created an accessible entrance in the courtyard between it and Manchester University’s 1901 grade II Rutherford Building but this was difficult to find as it was only reached via an arch on Oxford Rd. As the museum’s remit was to use the chance of expansion to grow and diversify its audience, we had to address this – not least because our new South Asian Gallery needed to go into that courtyard space.
How did you deal with the new entrance?
There had been a lovely arched entrance in the annexe building in the past but re-using it was ruled out as it was accessed up stone steps and far too narrow for emergency egress. The client wanted an Oxford Rd entrance, but as it’s listed, we had to consult Manchester city planners’ conservation team, Historic England and the Victorian Society. It meant breaking the Haworth elevation by removing a stone window sill and transom. There was a lightwell in front with iron railings, which had to be filled in and railings (and basement lights) reconfigured, and highway stopping-up was needed to allow for the ramp access. Stopping up involved months of negotiations with the city highways department and could only start once we had planning and listed building consent. Building it required the road to be dug up – with university data and electric cables running through it – a co-ordination nightmare. The curious layout of the ramp’s stone paving intimates the line of the former lightwell.
The new entrance is quite understated
We wanted to keep it really simple, but it’s also informed by Part B regulations for escape. We couldn’t have doors opening onto the ‘highway’ section of the ramp so inner bi-parting doors open outwards and the full height oak outer oak-board doors rebate into the oak side walls to allow clear escape widths. This gives the impression of a ‘doorless’ entrance, which we all liked. An architrave on the inner doors lines up with where the stone transom was – a historical reference to it.
What about the new courtyard insertion to the rear?
As it’s set off a small lane to the university campus with limited access and grade II-listed buildings all around it, it was a challenge to build – luckily we were able to plug into the 2003 Ian Simpson entrance extension without further disturbing any of them. The extension was conceived as a ‘jewel box;’ a total of 750m² of lower-level gallery space with the new dedicated South Asian Gallery above. The massing was again dictated by city conservation and Historic England concerns – which was mainly about the roofline and how it connected to the buildings around.
To gain consent we did context studies to prove our proposal did not obscure existing elevations – which meant creating a narrow lightwell around the new building and linking it back with recessed glazed connections to maintain the legibility of the listed elevations. Then there were roofscape concerns. Views of the Haworth’s ‘Hotel de Ville’-style roof were sacrosanct to Historic England and our building line was set to the upper string course line of that building so we did not impinge on it.
And your formal approach?
Being a high-grade museum space, it’s conceived essentially as a highly secure decorated box. The upper level is expressed in 3D, formed, green faïence tiles from Darwen terracotta in Blackburn, influenced by Manchester’s 19th century terracotta tile traditions. We imagined the lower-level wall as mortar-bedded stone ashlar. But this was a D&B contract in which we were novated, and as a result of cost and buildability concerns, limestone facing panels hung off rails on rainscreen cladding were chosen. Honed panels were supplied for maintenance reasons.
Glazed areas needed to be 99% UV filtering, which accounts for their dark, highly reflective nature. One large floor-to-ceiling glazed opening is set into the wall of the exhibition space. The glass and frame are fully security-rated and can be closed off with blinds but provide a great shopfront for the museum on a lane much-used by students and staff. In the narrow lightwell on the perimeter we did not need to deal with direct sunlight, so glazed units are more transparent – allowing visitors to read the museum’s listed elevations beyond and for the Rutherford building to bring light into its study spaces. The east-facing pair of sawtooth roof lights to the South Asian Gallery have oak slat blinds outside to cut out direct light, so both exhibition halls can be naturally lit – or not.
What was the structural strategy?
It’s a hybrid steel and timber structure sitting on concrete foundations. There was a lightwell going to basement level running on three sides of the courtyard but we decided to place the piles further back than its retaining wall – 3.5m in fact – to ensure there’d be no effect on existing foundations. We have ground beams from this that cantilever out towards the three listed facades and the concrete slab and the steel structure sits on this. There are drained cavities on existing facades in the lightwell and movement joints between the new slab and old buildings. The interstitial glazed structure around is cantilevered off steel beams and impinges – but does not rely on – the listed facades, meaning that it can move and breathe as it always has and that our intervention is fully reversible technically.
Why the hybrid structure?
A lot of considerations informed the structural strategy. Our environmental sustainability advisor was keen on the cross-laminated timber floors in the steel structure to cut the project’s embodied carbon but they brought clear benefits in other ways. This is a working, academic site and we had to minimise site logistics where we could. Bringing in prefabricated CLT slabs and inserting them in the steel structure using a crane was much better than constant concrete deliveries. That said, the new ground floor sits on a raised steel sub-frame and is made of insulated polished concrete, with the CLT slabs installed at first floor and roof level.
Another concern was construction vibrations. The museum’s very delicate collections are all held in the basements and could have been damaged by the works. Monitors were installed on site and fed live data to both the contractor and client during construction to ensure agreed limits were not exceeded. Also, the new toilets that we installed in the old building were located above these collections so we had to ensure that if water leaked here it could never reach them. As a result, we fitted specialist tanking all along the floor and up the walls behind the integrated plumbing systems.
It’s a highly serviced building – how was this co-ordinated?
Air handling happens in the suspended ceiling void below the CLT soffit, with a high level perimeter feed and central extract for the main gallery spaces. Main service risers run up either side of the new gallery entrance. The client wanted to maintain the potential for a roof garden as this is visible from windows facing the courtyard, so future loadings have been accounted for and heavy plant is on a flat roof of the 2003 extension, leaving the rooflights as the only elements at roof level.
The suspended ceiling has electrical and data tracks installed to allow for fully flexible exhibiting and lighting. Metal ceiling panels are acoustically insulated behind to create requisite acoustic levels in the gallery spaces. And there’s a resilient layer in the first floor timber floor to deal with visitor footfall.
900m² for £12m seems expensive
Museum consultants were appointed to ensure that we met international exhibition-grade spaces. That’s not just about the servicing of the galleries but includes minimum heights for exhibits as well as reinforced floors to allow for cherry pickers, museum grade ancillary spaces, air tightness criteria and security design for wall build-ups. On top of these, logistics issues concerning single-point site access and accommodating the needs of a working university campus all added to the cost of the D&B contract. But yes, it was £13,000/m².
As told to Jan-Carlos Kucharek