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Healing hand

aj building study

John McAslan's new wing for Benenden Hospital in Kent and the conservation of the matching listed wing from the 1930s are successfully completing a scheme that failed in earlier attempts

Thomas Smith Tait, the most influential Scottish architect of the inter-war period, died in 1954 at the age of 72. John McAslan, born in Glasgow in the same year, greatly admires Tait's work and was thrilled when his practice was commissioned to partially restore one of the latter's works and to design a new building in close proximity to it.

John McAslan + Partners (JMP) had no past experience in the design of hospital buildings, so the new clinic at Benenden Hospital in Kent was a challenge. Where the practice scored was with its proven expertise in restoring and extending iconic modern buildings, ranging from a Frank Lloyd Wright campus in Florida (AJ 22.11.01) to the Peter Jones department store in London and the De La Warr Pavilion at Bexhill-on-Sea.

It was the last of these, in which JMP has been involved for nearly a decade, that attracted the attention of local planners when the hospital proposed a possible new building adjacent to Tait's Lister Wing (completed in 1937 and now a listed building) and led to a detailed masterplan report in 1999. Planning permission and listed building consent were obtained in 2000, with the support of English Heritage, and the new building was completed late in 2002.

A partner in the practice of Burnet, Tait & Lorne since 1920 with that great Classicist Sir John Burnet (1858-1938), 'Tommy' Tait was schooled in the Beaux Arts tradition, but was open to more progressive influences. It was a matter of horses for courses. St Andrew's House in Edinburgh, which Tait won in competition in 1933, was certainly influenced by the work of Dudok. Elsewhere - at Adelaide House, next to London Bridge, and the frontage of the Daily Telegraph building on Fleet Street, for example - Tait returned to monumental Classicism. As architect in charge of the 1938 Glasgow Empire Exhibition, he designed the legendary 'Tait's Tower', the symbolic, and dynamically Modernistic, structure that put the exhibition on the world map.

'For Tait, Dudok was a very infectious disease', one of his assistants remarked, referring particularly to Burnet, Tait & Lorne's Infectious Diseases Hospital in Paisley, completed in 1934.Dudokian influences were even more evident in the Royal Masonic Hospital in London, with its finely crafted brick cladding.

At Benenden, Tait turned to a more lightweight aesthetic, perhaps inspired by Duiker & Bijvoet's renowned Zonnestraal Sanatorium at Hilversum. The designs also reflect more than a sidelong glance at the Bexhill Pavilion (Tait chaired the jury that selected Mendelsohn & Chermayeff 's scheme).

The two-storey wing contained wards along the southern edge, opening to a terrace and first floor balcony - the walls are meant to dematerialise in pursuit of fresh air - with a spine of service spaces to the north.

Fully glazed to the south, the building's north-facing facade is of load-bearing brick.

Benenden Hospital had been founded in 1906 'to accommodate the lower-salaried tubercular cases', with special provision for civil servants and Post Office employees.

The site was, and is, superb, with views south across the Weald. Today, the 145-bed hospital, run by the Benenden Healthcare Society and still independent of the NHS, offers a wide range of treatment, with specialities in endoscopy and gynaecology. Its buildings reflect a process of somewhat random development over the past century. In the early 1950s, Oswald Pearce was commissioned to design the Williams Wing as a close copy of Tait's building. The two blocks were connected by a clumsy three-storey link - the western 'bullnose' end of the Lister Wing was demolished as part of that project.

Within 40 years, Pearce's building had become a serious problem, with spalling concrete and water penetration leading to its closure. The potential for repairing and converting it was explored but this course was judged impractical. The proposal to demolish it was uncontroversial, given the undertaking to restore the lost integrity of its listed neighbour.

Few original drawings of the Lister Wing could be found, so JMP's reconstruction of the lost end relied on a close survey, with specialist fabricators manufacturing steel windows to match the originals and the (remarkably thin) concrete roof extended with the advice of Arup. Tait's building is in good condition throughout, though it would benefit from a general overhaul (now under way). JMP project architect Richard Ellis says English Heritage was concerned principally with the facade and the retention of the plan, so there was no funding for a strict restoration.

The new clinic occupies the same site and orientation as the Williams Wing - a conscious decision on the part of JMP.With the former link block removed, a connection had to be made with the Lister Wing and other hospital buildings (very ordinary masonry clad structures of the 1980s and '90s) to the north. This has been elegantly achieved as a deliberately neutral connection, well set back and externally rendered.

The plan of JMP's addition has a simple rigour typical of a practice where Louis Kahn has always been a prime influence. The treatment of the main facade has echoes of another McAslan hero, Glenn Murcutt. The brief was for a mix of consulting rooms and procedure rooms for minor operations, plus waiting and support spaces. Both inpatients and out-patients are treated here.

The plan places consulting rooms along the southern edge at first floor level. A central corridor separates these rooms from WCs and other facilities. The procedure rooms are accessed via a corridor along the northern edge of the building. Cantilevered at first floor level, it is connected directly to the blocks to the north. About 50 per cent of ground floor space is dedicated to sterile areas for the storage and preparation of surgical instruments and other material; the remainder has yet to be fitted out but is unlikely to remain vacant for long. Access stairs to the exterior are provided at each end of the building in fully glazed 'bookend' enclosures, recalling the glazed bullnose ends of Tait's original Lister Wing.

Constructed on a steel frame with floors formed on precast concrete planks, the new clinic is a straightforward and economical structure. Servicing requirements are moderate - consulting rooms and communal spaces are naturally ventilated - so connections can be discreetly accommodated within ceiling voids. The preference of the planners (and the architects) was for an undemonstrative new building that made no attempt to ape the style of the 1930s, nor vie for attention.

Before the Second World War, with the battle against tuberculosis the main concern, Tait opened his southern facade to the sun. In fine weather, the windows of the wards would be wide open with some patients lying in the open air. Consulting rooms need to be private places and those in the new clinic have both opening windows and blinds. Solar gain is controlled by the wall of fixed louvres standing forward of the facade. The landscape can still be glimpsed from inside the building; externally the effect of the solar screen is to provide the southern facade with a layered, essentially neutral, look. In visual terms this is a deliberate move: Tait's building can again be read as an elegant, virtually freestanding, glazed pavilion in the landscape. To the rear, where it closely abuts other buildings, the clinic is simply rendered, a cheaper alternative to the brick used in the '30s.

As a sensitive but far from timid response to historical context, JMP's building is everything one would expect from its architects.

For patients and staff, the facilities it offers are a huge improvement on those previously available. Internally, and this doubtless reflects a tight budget, spaces are less than generous. The building is one element in a large medical complex and extensive communal spaces were not required, but the reception would have benefited from being less cramped - its floor area is only a little larger than that of the escape stairs. Internal finishes are certainly economical, though an element of strong colour is used in communal areas to good effect.

It is unfortunate that the budget - which at £2.8 million for 1,858m 2represents very good value - could not have included provision for new furnishings. One decent work of art could do a lot to lift the spirits, which is, or should be, part of the process of healing bodies. A sound and strong building like this deserves furnishings of comparable quality. The architects say they are confident this will follow, and have already donated new reception seating to begin this process.

For all its modest scale, this project contains lessons that NHS clients, charged with far larger commissions, could advantageously study.

Structural strategy

The project comprises four different elements:

the new two-storey building, known as the Jubilee Wing, contains consulting rooms, sterilisation areas and procedure rooms plus plant rooms;

a new three-storey block south of the existing Queen's Ward, known as the link building. It connects the ward with the Jubilee Wing and the 1930s Lister Wing.

The building contains a lift, stairs and a plant room at level three;

two discrete two-storey corridor structures, which provide access from the link to the Jubilee Wing and the Lister Wing. The bridges allow differential movement of the three main building zones by the provision of movement joints; and lreinstatement of the western bullnose of the Lister Wing building.

The new buildings are braced steel frames at a grid spacing of maximum 6m.

Ties are provided perpendicular to the primary spans. The beams at each floor are typically positioned within the depth of the floor slab using a 'slimfloor'style arrangement. This system was chosen to match the existing floor-to-ceiling heights and to minimise the structure, to leave maximum space for services. The floor-toceiling height was so critical that welded plates on the underside of the I-beams could not be used to support the precast concrete floor panels as they do in actual slimfloor construction. Instead, the bottom flange of the UC sections used as primary beams support the precast panels. The top flange of the UC had to be cut away over a length sufficient to allow each panel to be inserted into the zone between the UC flanges, before being slid along the span into position.

The floor slabs are formed using precast concrete panels with an in-situ concrete topping joining the panels together into a stiff diaphragm. At ground level, the precast panels bear directly onto the foundations, which consist of mass concrete trench-filled strips and are founded on the Tunbridge Wells Sand Formation.

The western bullnose of the Lister Wing was reinstated. It has an in-situ slab at level one, supported on masonry stub walls down to the pad foundations. The 190mmthick slab at level two is supported on masonry walls within the building and at its two ends by arcade beams.These beams are curved and located at an inner and outer perimeter, supported on a series of steel CHS posts. The 170mm roof slab cantilevers out over either the main masonry cross walls or the inner arcade beam, supported by CHS posts. The reconstruction of the building reinstated the original structural configuration.

Services

The new wing has a hierarchy of services. The consulting rooms on the south facade are naturally ventilated. However, there was a concern that full-height glazing of rooms on the southern facade would lead to excessive solar heat gain, which was confirmed by analysis predicting internal temperatures in summer. A bank of external louver blades was incorporated to provide shade to the glazing in summer when the sun angle is high, but to allow daylight through in winter when the sun angle is low.

The ancillary rooms are treated with mechanical supply and extract systems, controlled by a centralised building management system.

Specialist areas within the new wing were discussed in detail with the hospital. The gynaecology and endoscopy procedure rooms have a dedicated mechanical air supply and are maintained at a negative pressure to avoid the spread of contaminants. In contrast, the clean production area, where the sterilised surgical equipment is packed and stored, is kept under positive pressure via another dedicated mechanical supply to prevent contaminants entering the space. Night-time set-back and a standby motor ensures this area is pressurised 24 hours a day.

To save cost, the feasibility of using an existing steam main instead of new gas boilers was studied with the hospital. Detailed coordination of steam and condensate mains through congested existing ceilings, and some aesthetic compromises round the back of the new building, allowed the steam main to be used.

A similar but less complicated arrangement allowed the deletion of new chillers and connections to existing boosted chilled water circuits, saving both plant space and installation costs.

The electrical and public health services design were discussed in depth with the hospital to ensure all the relevant hospital standards were adhered to. The project was successfully carried out without major disturbance to the existing hospital's activities.

CREDITS

TENDER DATE 2 February 2001

START ON SITE DATE 23 April 2001

CONTRACT DURATION 52 weeks

GROSS EXTERNAL FLOOR AREA 1,820 m 2

PROCUREMENT Two-stage selective tendering; JCT 98 with Quantities

TOTAL COST £2,823,856

CLIENT Benenden Hospital Trust

ARCHITECT John McAslan + Partners: Adam Brown, Richard Ellis, John McAslan, Fanos Panayides, Michael Pepper, Andrew Pryke, Anne Wagner

QUANTITY SURVEYOR Faithful & Gould

CONSULTING ENGINEER Arup

HEALTH TECHNOLOGY AND MEDICAL PLANNING CONSULTANT Robert Owen Associates

PLANNING SUPERVISOR Hurley Palmer Flatt

SUBCONTRACTORS AND SUPPLIERS Curtain walling, windows Mag Hansen; insulation Rockwool (Rockshield); roofing Euroroof; blockwork Tarmac Topblock; blockwork restraints Ancon; doors Leaderflush; ironmongery Laidlaw; tanking, DPM Grace; brise soleil, louvres Colt; primary steelwork Graham Wood; drylining British Gypsum; mechanical subcontractor Sladdens; electrical subcontractor Parsons

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