Associated Architects has taken a disused Royal Mail sorting office in Birmingham and transformed it into Mailbox, an innovative, iconic urban space and a new gateway to the city
There are very few, if any, precedents for Birmingham’s giant Mailbox. It is marketed as the largest mixed-use building in the UK, offering more than 100,000m 2offloor space and comprising two hotels, 16 restaurants and bars, 200 roof-level apartments, offices, shops, a 1,000-space car park and more. There are many ideas at play, not least the robust stroke of cutting a street straight through its heart to provide a handy pedestrian link between New Street Station and the canalside convention quarter.
The Mailbox possesses its name and inevitable red render because it was created from the shell of a Royal Mail parcel and letter sorting office. Although it is the largest job its designer, Associated Architects, has taken on by far - with a huge 12m x 12m column grid and complex changes in level and scale - it never breaks free from the controlling intelligence. And as a regeneration scheme, the practice has also undertaken further adjoining wharfside buildings - the mixed-use Washington Foundry and Salvage Wharf, and a purposedesigned restaurant for Fish! Part of the canal has also been excavated and a new bridge and delightful cone-shaped tower built to house a lift and staircase, which the architects call the node.
The old sorting office, to the south-west of the city centre and sitting just outside the elevated inner ring road, was the largest automated mail-processing building in the world and easily Birmingham’s biggest building. It was built in the late 1960s, large and squat with unadorned concrete and curtain walling, but serviceable and surprisingly unassuming. It had a basement tunnel to nearby New Street Station and large-scale openings for articulated lorries. It employed thousands of people during the 1970s - then more of an industrious behemoth than a white elephant as it was still in use, albeit on a reduced scale, until the Mailbox development started.
The contract to strip out the machinery alone was worth £1 million.With the generous grid augmented by 6.2m floor-to-ceiling heights and massive floor-loading capacity, it gave the architect unparalleled flexibility in which to work. ‘It was built on a heroic scale, ’ says architect Ian Standing, ‘but it sat between other buildings with its base below the ring road and, because the site rises more than 12m to the canal, the change of height meant it didn’t seem so dominating.’ Clearly, there was no question of demolishing the building and starting again. With an open brief, a developer committed to quality, a co-operative city council excited by the tourism possibilities, and a grid size only to be dreamed of in a new building, the sorting office could be transfigured and redefine the area.
The idea of making the Mailbox a route rather than a destination is central to the scheme. The development is conspicuously upmarket, with designer retailers such as Armani and Christian Lacroix, the four-star Malmaison Hotel and Crosby Homes’ rooftop apartments at £350,000. But the street, open to the elements and Birmingham’s many inhabitants 24 hours a day, ensures vitality over bloodless ‘executive’ gated communities, even if many of the people passing through can only afford to window-shop.
The street, named Wharfside Street, offers a coherent pedestrian and, importantly, tourist route for this part of the city centre for the first time. People are drawn from the Navigation Street entrance of New Street Station, just 300m away to the new Mailbox Square, under the elevated roadway and up and through the grand portal which reaches two-fifths of the building’s height. It is 12m wide and cuts through the rectilinear plan of the building, rising 18m to the canalside exit, where it opens out to the waterside bars and restaurants, the canal network, new bridge, student housing and beyond. This side of the building is an urban oasis, where the city centre stretch is slowed to at least a calm, unhurried stroll and the waterside views can be enjoyed.
Externally, the building is treated simply.
The Mailbox Square elevation, onto which the Malmaison hotel and retail units face, is the most radically remodelled. Graded steps address the changes in level in front of the building and provide piazzas and landscaped areas. The old horizontal concrete panelling has been verticalized for a much stronger statement. A stone-and-glazed base rises either side of the new opening, followed by the red rendered element, broken for more glazing above the portal. This is capped by a clerestory strip of glazing, then metal louvres and a projecting roofline. But, despite the post-office-red expanse, the experience is appealingly civic, not corporate.
At the canal end of the building, metal walls act as a foil to the south-west waterfront. But, elsewhere, intervention is kept to a minimum to accommodate further development as the need arises. Simple zinc panels and metal windows replace the curtain walling between the horizontal concrete panels, acknowledging the building’s industrial past. Staircases at the corners are clad in glass channels, backlit with blue neon. The entire building is lit dramatically to include the ring road undercroft.
The hotel has its entrance in Mailbox Square, to the right and below the streetline, but it bridges the portal and sandwiches the retail units that are visible at the entrance to Wharfside Street. The hierarchy of spaces and uses was crucial to the viability of the development. Developer Alan Chatham, (fresh from the success of Brindleyplace) and Associated Architects discussed multilevel retail at length, and decided to use it, despite received wisdom being against the concept. On entering the Mailbox there are two floors of retail space arranged so that one level is at grade with the entrance, the other at grade with the next level at the top of Severn Street, where there is an exit.
Escalators link the two floors.
Internally, the street is broken into smallscale elements with different treatments reflecting the different uses. Detail is more sophisticated than in the exterior, and architectural effort has been concentrated here, with the huge grid resolved in more varied ways and the height controlled to echo the scale and character of a typical urban street.
Stonework is used as a base to red-terracotta piers inserted on a 6m grid throughout the retail areas, with stonework on the whole of the office level. This effect continues through the restaurant level as framing to shopfronts, as with the retail providing the controlling grid for individual designs.
The retail space ends at the mid point of Wharfside Street, where there is a generous landing to encourage people to pause and orientate themselves. This coincides with the external level of Severn Street. The office entrance is sited here, with a 12m-high foyer using bridges to link with the higher levels.
Office space is sited in the two wings of the street above the retail units, and in two complete floors at the rear of the building, each providing more than 6,000m 2of floorspace.
The tall floor heights will also allow for further mezzanine space.
The residential entrance is also sited at this point of the building, with concierge and lifts linked to the basement car park.
Birmingham has trailed behind the likes of Manchester and Leeds in the inner-city living phenomenon, although Mailbox represents something of a leap ahead. The apartments enjoy the highest levels of the building, using the large expanse of roof to create a courtyard with sprawling balconies and roof gardens.Views are expansive, though window sizes are rather mean. Further apartments are sited in the wings of the street using an existing floor level, with the roof again developed as a vacant site.
Rising a further storey, the street defines the restaurant area, exiting the building at the canal end where it has been cut back to form an elevated piazza. This links to the terrace of the adjoining Salvage Wharf development, connected to the graceful new metal footbridge that springs from a bluebrick cone (the ‘node’). The node supports the bridge, but is also designed to be a townscape marker visible from all long viewpoints into the area and positioned on the defining axis. The node has also proved to be a popular orientation and vantage point.
The Mailbox represents a vigorous approach to regeneration, which respects the complex histories of the surrounding buildings and topography. Birmingham is a robust, redbrick city and Mailbox is destined to become a bold, iconic addition.
The existing Royal Mail sorting office had a robust steel-framed structure with a column grid of 12m x 12m and floor-to-floor height of 6.1m. The main floor beams were 940mm x 305mm sections with 610mm x 229mm secondary beams (spanning the 12m) placed at 3m centres. Shallow precast units spanned onto the secondary beams acting compositely via the shear studs. The steel and concrete were tested and calculations carried out to determine the load capacity of the various elements.
The steel structure was founded on concrete pads, which were seated on the Mercia sandstone (originally estimated as having a 1,200kN per square metre bearing capacity). The flexibility and robustness of the structure allowed for the addition of mezzanine decks and structures on the roof - the building was originally designed to take an additional storey, with stub columns protruding through the roof deck.
A new open-air street was created through the middle of the existing building by demolishing the central 12m wide bay from ground level to roof. Temporary and permanent steel bracing were used until the construction of new cores, which provide permanent lateral stability, was finished. The new housing on the roof is of lightweight timber-frame construction and sits on a concrete-beam grillage supported off the existing roof beams. This created a service void, which was adopted for drainage from the houses. New steel plant enclosures at the existing roof level house plant-controlling services within the main building. The ground floor was demolished and raised to allow for extra parking.
At the east end of the building, new concrete mezzanine decks were introduced at all floor levels, with two new floors created above the original roof level. In addition, a new-build portion was added to the first two 12m bays of the northside. This complex structural refurbishment included the introduction of a large vierendeel girder at roof level from which to hang the floors. This portion of the building provided the shell and core for the new Malmaison Hotel. Excavation at basement level provided space for a leisure facility, including swimming pool.
Lightweight mezzanine decks in office and retail areas provided additional space at little extra cost. A mixture of steel and masonry was used for the structures on Salvage Wharf to reflect the canalside environment.
The ‘node’ structure is reinforced concrete with masonry cladding, its viewing gallery has a steel and glass roof. Fish! was constructed in tubular steel, glass and timber over a concrete basement structure connected to the basement level of the ‘node’. Lateral bracing was avoided in order to allow maximum freedom for openings in the walls. The circular steel columns were therefore fixed at the base, on top of the basement structure, and designed as free cantilevers.
The new Mailbox management offices were constructed within the old Washington Wharf Foundry building. The original timber roof trusses and timber purlins were held in place during the demolition of the main frontage, excavation of a lower-ground floor to towpath
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Curtins Consulting www.curtins.com
Gross floor area
All areas gross internal in m2
AREA EXISTING ADDITIONAL TOTAL
Retail 17,150 2,629 19,779
Offices 19,742 0 19,742
Leisure 2,443 372 2,815
Residential 3,762 7,321 11,083
Hotel 5,760 2,336 8,096
Cores - retail 360 0 360
Cores - office 1,700 0 1,700
Cores - residential 753 0 753
Cores - common 2,517 0 2,517
Car parking 21,275 12,356 33,631
Loading 1,816 0 1,816
Total 77,278 25,014 102,292
Total costs Percentage of total
Recladding elevations 4,215,002 11.07
Demolitions, alterations 1,404,144 3.69
Office cores 2,601,981 6.84
Existing shell: restaurants 43,488 0.11
Existing shell: car park 2,308,344 6.06
Retail core 917,155 2.41
Real Street: common works 2,781,041 7.31
Existing shell: offices 148,600 0.39
Base build works: residential core 105,028 0.28
Base build works: residential car park 563,844 1.48
Base build works: infrastructure 2,972,645 7.81
Loading and transfer area 46,685 0.12
New build: retail 1,117,271 2.94
Hotel 1,499,882 3.94
New build: leisure and restaurant 231,622 0.61
External works 418,880 1.10
Residential common parts M&E 763,864 2.01
Residential new build 5,287,603 13.89
Residential fit out works 4,083,167 10.73
Residential core 519,947 1.37
Residential car park 173,422 0.46
Provisional sums 1,012,846 2.66
Building subtotal 36,716,461 96.46
Fees 1,348,159 3.54
TOTAL 38,064,620 100.00
Costs supplied by Faithful & Gould
TENDER DATE Stage one August 1998 Stage two June 1999
START ON SITE 9 August 1999
CONTRACT PERIOD 63 weeks
FORM OF CONTRACT JCT with contractor’s design
CONTRACT SUM £38,064,620
CLIENT The Mailbox
ARCHITECT Associated Architects: Matthew Goer, Ian Standing
STRUCTURAL ENGINEER Curtins Consulting
CLIENT’S AGENT AND QUANTITY SURVEYOR Faithful & Gould
LANDSCAPE ARCHITECT Gillespies
CONTRACTOR, DESIGN AND BUILD MANAGER Carillion
CONTRACTOR ARCHITECT Weedon Partnership
MECHANICAL AND ELECTRICAL SERVICES ENGINEER Couch Perry Wilkes
ENGINEER (TRAFFIC) Arup ENGINEERS DEPARTMENT Birmingham City Council Transportation Department
ARTIST Thomas Heatherwick Studio and Mark Pimlott
PUBLIC ART CONSULTANT Modus Operandi
PLANNER Birmingham City Council Planning Division
BUILDING CONSULTANT Birmingham City Council Building Consultancy
LIGHTING CONSULTANT DPA Lighting
WORK FOR RAILTRACK mezzanine steelwork Cov Con; handrail and stairs Hubbards; raised access floor Hewetsons; partitioning Neslo; acoustic ceiling Profile Lighting Services; disabled lift Landmark Lifts
level and rebuilding of the first floor and front masonry walls.