Lifschutz Davidson Sandilands deserves a big hand for managing to squeeze an old-school cylinder-shaped building into a tiny London backstreet

In an era of wildly geometric architecture, there’s something distinctly old hat about a drum-shaped building. The cylindrical format was used in the 1960s for office buildings just off Kingsway in London and for the Bullring in Birmingham. Admittedly the Swiss Re tower of 2004 is circular in plan, but Foster and Partners turned it into an icon by adding its double-curved cigar profile.

Yet despite its unfashionable form, a cylindrical office building has just been dropped on to a tiny backstreet in Westminster, central London. Its architect is Lifschutz Davidson Sandilands and its developer IVG Asticus, a pairing that has already completed a couple of upmarket office conversions in London. In this case, the drum is not the sculptural whim of the architect. Rather, it is the result of the developer reverting to mercenary type by trying to wring as much lettable office space out of a given site.

The problem is the geometry of the site and the buildings surrounding it. The site is tiny in area, trapezoidal in plan and bounded on three sides by a nearly continuous wall of medium-rise brick buildings.

The pure cylindrical shape of the Asticus Building is clearly expressed in the stylish reception foyer
Credit: Chris Gascoigne@View
The pure cylindrical shape of the Asticus Building is clearly expressed in the stylish reception foyer

If a trapezoidal building were placed on the site, with its perimeter walls close up to the boundary, it would deliver the maximum floor area possible. But it would be blighted by limited daylight and eyeball-to-eyeball views of the neighbours straight ahead. By contrast, the perimeter walls of a cylindrical building curve continuously, leaving it with the shortest stretches of elevation facing the neighbours head on, as well as more daylight funnelled down through the empty corners.

A drum with an internal diameter of 28m has been fitted on to the site so snugly that the fully glazed perimeter wall rises just 1.5m from the boundary on two sides.

Paul Sandilands, director of Lifschutz Davidson Sandilands, acknowledges that the cylindrical building solution was inherited from Foggo Associates, which had already obtained planning permission and listed building consent to demolish the existing Victorian building on the site, Caxton Hall, which was listed grade II but derelict. That takeover took place when the German-owned developer Asticus bought the site from Amberswift, along with the design and planning consent.

Although the cylindrical building fits the site remarkably well, making it work on the inside presented several headaches. Here, again, though, Foggo had cracked the main problem. The standard solution in cylindrical buildings is to pack structural frame, toilets, lifts, stairs and services in the centre. But in such a narrow building as this, a central structural and services core would take a sizeable bite out of lettable floor space. Instead, Foggo had the bright idea of shifting the core to a “blister” that projects some 7m into the only spare corner of the site. The blister is barely visible from the street and leaves the interior of the drum entirely free as usable office space

A tight fit into a cramped site has not compromised the pure drum shape, as the services and access ‘blister’ has been tucked out of view at the back
Credit: Chris Gascoigne@View
A tight fit into a cramped site has not compromised the pure drum shape, as the services and access ‘blister’ has been tucked out of view at the back

Asticus was not content to leave it at that, however. It called in its own team of consultants to appraise Foggo’s scheme in detail and, after that, to rationalise and refine several aspects.

The biggest design change was to shift the mechanical plant from the basement to the rooftop, as Waterman Building Services reckoned the site was too tight to feed fresh air down into the basement chillers. This presented quite a dilemma. Westminster planners were adamant, first, that the height of the cornice line should not be raised and, second, that no rooftop plant rooms should be visible. But Asticus was determined not to sacrifice a whole storey of precious office space.

The dilemma was solved by the architect and Adams Kara Taylor, the structural engineer. The plant room has been visually lost by tucking it behind and sinking it down slightly into a coronet of projecting steel fins. Below the plant room, all 10 office floors allowed in the planning consent have been retained but compressed in height (see “The big squeeze”, below). And as a bonus, the top floor gains an exhilarating double-height space around the perimeter where the fins of the coronet crank up and over it.

The next change concerned the internal layout. The usual layout for ceilings, floors and internal partitions in circular buildings is radial like the segments of an orange. But as Sandilands points out, this can result in uncomfortable wedge-shaped rooms that are frowned on by tenants. Instead, a cruciform rectilinear layout was devised. This would be more cost-effective by accommodating standard square ceiling panels and straight air-conditioning ducts above them.

The four internal structural columns were spread out at intervals of 10.66m. This arrangement leaves four “orange segments” in the corners without suspended ceilings or ductwork. But they are supplied with conditioned air through the downstands of suspended ceilings around their perimeter and lend themselves to use as executive offices or meeting rooms.

Unimpeded by a service and access core, the interiors benefit from space and all-round views to the surrounding city
Credit: Chris Gascoigne@View
Unimpeded by a service and access core, the interiors benefit from space and all-round views to the surrounding city

Finally, the detailing of the perimeter envelope was slimmed to increase usable floor space (see “From the outside in”, below). Foggo’s scheme adopted the standard formula of a loadbearing perimeter grid of precast concrete columns and beams. But this was switched to precast casings that enclose slender columns, which formed an integral part of the building’s overall structural system of in-situ concrete. Being lighter and slimmer than load-bearing columns, the casings eat up less usable floor space and also less window space.

As a result of these various refinements, usable office space amounts to an efficient 83% of the total gross internal floor area.

In the event, none of this work to reconcile the demands of planners and developer has compromised the building’s architectural quality. In the hands of Lifschutz Davidson Sandilands, the process was more one of refinement and it is this, not the conflict between planners and developers, that shows in the finished building.

On the outside, the drum with its projecting precast concrete window bays is more delicately modelled than Richard Seifert’s rugged Kingsway building. The topmost coronet is even more exquisitely detailed and makes a splendid landmark on the dense city skyline.

On the inside, each office floor has a wonderful sense of space, free of internal obstructions other than the four narrow, widely spaced columns. The floor-to-ceiling glazing adds to this sense, as well as providing panoramic views out to the Palace of Westminster, Buckingham Palace and other famous sights.

How remarkable that such a gem has resulted from the developer’s insistence on squeezing the maximum floor space out of the site.

The big squeeze

As with many city-centre new-builds, fitting in the maximum number of usable floors beneath the cornice height laid down by Westminster planners meant compressing the storey heights of the Asticus Building. The problem was aggravated when the building was redesigned by switching the plant room from the basement to the rooftop while retaining the original cornice height.

The original design team adopted a standard solution to the problem of compression, which was to post-tension the concrete floor slabs so as to make them stronger and thinner. But this option was rejected when Adams Kara Taylor took over as structural engineer.

“On a circular building, post-tensioning brings complications,” explains project engineer Steve Toon. “You need to have jacking points that project all round the perimeter. These clash with fixings for the cladding panels, so the whole facade becomes bulkier.”

So Adams Kara Taylor fell back on conventional in-situ concrete construction for the entire structural frame of slabs and columns. The floor slabs were kept as thin as possible by combining a flush soffit without downstand beams with a pre-camber that added strength to the slab as the freshly cast concrete settled down to a level surface as it cured. The thin slabs also called for high-density steel reinforcements, which were made even denser by slimming down the vertical supports to just four internal columns of 800mm diameter at relatively wide intervals of 10.66m and 36 perimeter columns measuring 300 × 300mm in section.

As partner Albert Taylor says, “All this involved a huge amount of analysis. But the frame shot up quickly, with Ground Construction as specialist contractor.
And the floor slabs ended up just 320mm thick, which is only 20mm more than post-tensioned slabs.”

Getting cost certainty

Construction management, rather than a lump-sum contract, is the procurement method favoured by developer IVG Asticus.

It appointed ISG InteriorExterior for the £16m, 80-week contract.

“We like construction management because we are more hands-on than other developers and it allows us to meet the trade contractors,” says Matthew Mason, development director at Asticus.

“We operate construction management successfully by fixing 85% of the specialist packages within six months of start on site. This gives cost certainty to the risky packages such as M&E and cladding. We leave the internal finishes, which are lower risk, until later.

”The job was genuinely delivered below budget and on time,” he adds proudly.“And we all remained friends all the way through.”

From the outside in

The external envelope was one of the trickiest aspects of the design. To speed up construction, the integrated loadbearing system proposed by original architect Foggo Associates was split into two separate components: in-situ structural columns and external casings in precast concrete.

The new team also planned to combine the precast concrete casings and the glazing in a single package, as this would hand the responsibility for procurement, design, production and installation to one organisation. But this created another headache. “It was difficult to procure the combined cladding package because it was too small for a bespoke international system but too complex for a domestic stick-type cladding company,” says Paul Sandilands, director of architect Lifschutz Davidson Sandilands. “In the end, the £3.5m contract was awarded to Felix, which subcontracted the precast concrete casings to Decomo of Belgium.”

Entire bays of precast casings were fabricated and fully glazed off-site by Felix. When delivered to the site, the modules weighing 3.7 tonnes each were craned directly into position and bolted to the concrete floor slabs and columns. Internal casings in pressed aluminium were also part of the same package, but installed later.