星空传媒

The current craze for self building has resulted in some outstanding and ambitious residential projects, but one currently under development in Chelsea surely tops them all. Topping out has just taken place on a conversion of the Victorian former King鈥檚 College building on Manresa Road into apartments that are being billed as possibly the most luxurious in London.

Julian Simmonds, a former executive vice president of financial services giant Citigroup, noticed the elegant fa莽ade of the 1895 built structure stretching for some 100m along Manresa Road while house hunting, bought it and gained planning permission for conversion to residential use. The project is ahead of schedule to deliver 15 duplex, triplex and penthouse apartments offering the clear space usually found only in Docklands loft conversions along with a level of exclusivity and luxury seldom found anywhere.

Simmonds brought in Candy and Candy as co-developers to provide shell and core apartments that will cost between 拢7m and 拢15m each. Thanks to the choice of a structural steelwork frame to support the apartments behind the retained fa莽ade, residents will have a great deal of freedom in how they use the interior space. Fitting out to the purchasers鈥� specification will cost an additional estimated 拢7m for each apartment. The development is being described as 鈥榚ight star鈥� to signify the level of luxury that is being built in.

Simmonds says Manresa Road will offer residents 鈥渇lexibility, huge rooms, an M&E specification that鈥檚 never been done before and a flexible structure鈥�. The M&E specification includes full air-conditioning with humidification and air cleaning, and the choice of heating by warm air, underfloor, or radiators. An uninterruptible power supply will provide 48 hours鈥� backup in the event of a power cut. And all the plant is designed to cope with the theoretical maximum number of people the apartments could hold, about 1500. According to Simmonds, the quality will be unprecedented in the residential sector, and residents will have the flexibility to create big rooms of 40ft to 60 ft.

Ready-made history

21 Manresa Road was designed by the architect J M Brydon and completed in 1895 for South-West London Polytechnic. During the 1930s it became Chelsea School of Art. In 1985 the building was transferred to King鈥檚 College London, which used it as a research facility until 2002. The new structure is divided into eight 13m wide bays running from front to back, comprising 15 apartments, eight of which are single width triplex units, four double width duplex units, and three triple width penthouses. There is a raised ground floor, a first floor, a mezzanine level and a second floor. Room heights are dictated by the existing windows and will be around 4m. In the duplex apartments, the mezzanine floor will be made of timber on Metsec purlins, allowing it to be moved, if desired, to create a stunning double-storey space.

The original concept design was in reinforced concrete, but this was changed for steelwork when structural engineer Michael Barclay Partnership was brought into the project. 鈥淲e put forward a steel option because we thought going for wide-span construction would give the interior designers and architects a lot more freedom,鈥� says partner Tony Hayes. Concrete would have meant using internal columns, or beams of a greater structural depth that would have carried a penalty of reducing the storey heights. 鈥淲e came up with a steel alternative that removed four internal columns in every unit, and confined the structure to the line of the party walls,鈥� says Hayes.

Universal columns along the party walls at 2m centres support cellular beams spanning the full width of each apartment, to create column-free spaces. 鈥淏ecause the client is selling the apartments as shells we wanted to give them a blank canvas, so they wouldn鈥檛 have to go back later and employ another engineer if they wanted to remove a column or modify the structure,鈥� says Hayes. 鈥淭he beauty of the scheme is that we can generate a service zone within the depth of the Fabsec beams.鈥�

Hayes said the design is aimed at maximum flexibility, not maximum elegance of the structure. So although there is more steelwork than could have been needed, the design succeeds in terms of the flexibility it provides the end user to change the interior around.

Design of the cell beams - undertaken by steelwork contractor Bourne Steel - was complicated by a number of factors, such as the number of holes for services. 鈥淭here are 300mm holes at 450mm centres, with a number of additional holes for ductwork over and above that,鈥� says Rob Sperring, project manager of main contractor Multiplex.

An unusually onerous deflection criterion applied. The deflection of the cellular beams under subsequent fit out loads, both imposed and dead, is limited to 1/750 of the span rather than 1/360. This is partly to protect the apartments鈥� expensive finishes such as marble floors that would be at risk of damage. The beams are pre-cambered to take out deflections under construction loads.

The specification is extremely high in all parts of the project, as can be seen in the attention devoted to preventing sound propagation. No special acoustic measures are needed for steel framed structures, but the developers decided on a 鈥渂elt-and-braces鈥� approach. As a result, the primary beams in each unit run from front to back of the building, one on each side of the main columns and supported by brackets. Blockwork party walls are built off these beams so that between each dwelling there are two walls separated by a 700mm void, which also acts as a vertical service duct.

People like working on a prestigious site. we鈥檙e spending the money we need to get a good job

Julian Simmonds, developer

Both the primary and secondary beams rest on Tico acoustic attenuation pads. In addition the fixing bolts are fitted with sleeves, collars and washers to prevent sound transmission. Vertical sound transmission is dealt with by the composite steel/concrete floor construction, with 150mm concrete on top of Richard Lees Holorib decking. Residents are thought likely to add over 100mm of their own finishes, probably with resilient material beneath, so effectively there will be 250mm of concrete on top of the beams.

Demolition of the old structure began in January 2004 and steelwork contractor Bourne Steel was integrated into the design phase from late summer 2003, with steelwork erection starting on 16 December 2004, once basements works had been completed. 鈥淓veryone said we were crazy starting four days before Christmas,鈥� says Sperring. 鈥淏ut it highlighted a number of problems which Bourne worked on over Christmas. It gave us momentum so that when we came back in January we could hit the ground running.鈥�

Cherry picking problems

The huge tubular bracing members supporting the retained fa莽ade, which crossed the site diagonally created an access problem which Bourne Steel overcame by bringing in two special Genie cherry pickers with telescopic booms fitted with 鈥渄roop snoots鈥� or articulated arms, which gave them a reach of 25m.

鈥淭hey could stand outside a bay and reach back to the far side of the bay next door,鈥� says Bourne Steel divisional manager Rod Potts. Another benefit of the machines was that they allowed the steelwork to be fixed without erectors having to walk on the steel itself, which enhances safety.

Steelwork was installed bay by bay, with the cherry pickers standing on the garden area and erecting the steel to its total height at the front and cascading back. Following trades were able to start work sooner than would have been possible by constructing one level at a time over the complete width.

Steelwork installation was completed ahead of schedule in June, despite a design change to the roof steelwork. Angled rafters were introduced to form the profile of a mansard roof at penthouse level. 鈥淭his transferred loads all over the place,鈥� says Potts. 鈥淭he rafters were picked up by the gable beam, which needed a column to the second floor. Some of the beams that were already in fabrication had to be redesigned.鈥� Changing the construction sequence allowed between two to three weeks to be recouped.

Having a private individual as a client seems to have helped with fostering a strong co-operative relationship between members of the construction team. 鈥淲e have a good relationship with Multiplex,鈥� says Potts. 鈥淚n site meetings we sit down and thrash out problems without animosity.鈥� Multiplex鈥檚 Rob Sperring says: 鈥淎ll the contractors are here because we want them to be. Bourne was selected because they鈥檝e worked with us before and are recognised as a non-adversarial company who deliver.鈥�

All agree that the on-site atmosphere has been helped by the close personal attention given to it by Simmonds himself, who is on site most days. There is a feeling on site that this is a unique project. Simmonds says: 鈥淚鈥檝e been very happy with Multiplex and all the subcontractors. There鈥檚 a good relationship between all of us. People like working on a prestigious site; we鈥檙e spending the money we need to get a good job, being fair, and people have responded very fairly.鈥�

The first apartments are due to be handed over to their new owners in September, and the development is certain to become one of London鈥檚 most prestigious addresses.