Feature

A Tardis in King's Cross

The Institute of Physics has harnessed the power of concrete to create a cavernous, slightly sci-fi space behind a row of Victorian shopfronts, writes Tony Whitehead

The new headquarters of the Institute of Physics is not an imposing building, at least not from the outside. Strolling past its frontage on Caledonian Road, King’s Cross, you might miss it altogether – and that’s partly the idea.

Set as it is opposite a quaint Victorian crescent, and among a busy mixture of shops and restaurants, local planners were insistent that the size and massing of the IOP’s new 2,400m2 premises should not disturb the pleasantly human scale of its locale. The IOP agreed, says Harish Ratna, project director at architect TateHindle: “The client too wanted a building that would engage with, rather than dominate, its neighbours here in the ‘knowledge quarter’ of King’s Cross.”

So the site’s front facade, a row of 19th-century shops with two floors of ‘living over’, has been largely retained, its weathered brickwork now supported off the new in-situ concrete-framed building. The same applies to the IOP’s rear facade on Balfe Street which, running at an angle to Caledonian Road, gives the building a distinctive V-shaped plan. A new fourth floor is set well back behind a balcony so as not to loom over the streetscape.

The outlines of the Victorian retail units are now framed by precast concrete elements in grey with a medium-heavy acid etch to produce a stone-like texture. The old sashes have also been replaced with full-height glazing, providing literal shop fronts for the IOP – “a showcase for its activities”, as Ratna puts it.

Curious passers-by can peer into the IOP’s ground-floor Accelerator Centre – not a sub-atomic particle smasher, but a science-friendly environment for physics-related start-ups. Elsewhere in the building are seminar rooms, two floors of offices, a council chamber and, in a newly excavated basement level, exhibition space and an auditorium.

Entering the building from its low-key Caledonian Road entrance, one is immediately struck by two things: the bold use of exposed concrete and the surprising amount of space. The concrete aesthetic is accentuated by grey fabrics, and prominently positioned metallic lift doors lend an almost retro, science-fiction feel to the interior. Meanwhile, thanks to the V-shaped plan, the building widens out unexpectedly to a full-height atrium where a wow-factor internal balcony overlooks the large basement-level exhibition space. “The scale is not what you might expect after the impression you get from the street,” agrees Ratna. “It is like a Tardis – which I guess is quite appropriate.”

The Doctor would no doubt feel at home here: the roof is fitted with a cosmic ray detector and the building is trialling Li-Fi – a light-based version of Wifi with up to 1,000 times the bandwidth. A large interactive screen in reception is dwarfed by an even larger one in the exhibition space which has been used to teleconference with the International Space Station. Today it is showing dramatic video of our boiling sun.

It’s no surprise that the building design should actively seek to exploit the physics of concrete. “The IOP’s ambition is to put physics into action,” says Ratna. “It wanted to reflect this in the building, and this is one reason we went for concrete. Exposed concrete helps with sustainability, in that it reduces the need for other finishing materials such as plasterboard. But in particular, we wanted to exploit its thermal mass to reduce the load on the building’s heating and cooling systems.”

To facilitate this, almost all the ceiling soffits in the building are formed from the exposed underside of the concrete slabs. The columns are also exposed in-situ concrete, as are the majority of the walls. Having so much concrete in direct contact with the air allows it to absorb heat produced by sunshine, people and electronics, releasing it overnight when the building is vented. Alternatively, in winter, heat can be retained to reduce active heating requirements the following day.

“What the thermal mass gives us,” explains Ratna, “is a useful time lag. So in summer, cooling does not need to be switched on until later in the day, if at all. Similarly, in winter heating is kept to a minimum. The building has just a small boiler to help on the very coldest days.”

The thermal mass effect works in tandem with a low-energy M&E system featuring GeoKOAX geothermal heat pumps – the first-ever UK deployment of this technology. These work like normal heat pumps, sending water down boreholes to allow the near-constant temperature of the ground to heat or cool it as required.

This is used to moderate the temperature of air being drawn into the building via playfully designed zinc-clad “chimneys” on the roof. The air is then circulated through voids under the raised floor of each level where it interacts with the temperature of the concrete before filtering out into occupied spaces via floor-mounted diffusers.

“We sank the boreholes and then cast the basement slab around them,” says project architect Chinedu Soronnadi. “Usually these boreholes would need to be something like 150m deep, but the GeoKOAX technology uses wider bores and swirls the water around to increase the exchange of heat. As a result, our boreholes need only be 75m deep.”

Solid steps

The IOP has two staircases: one “back-of-house” which was completed early and used as contractors’ access, and one that, while more of a “designer” staircase, still exhibits the IOP’s distinctively industrial style.

The latter (above) is made from steel stringers but features precast concrete treads. “We originally conceived the treads as steel, but were concerned about noise and slip resistance,” says TateHindle’s Chinedu Soronnadi. “The concrete gives a safer, more solid feel. To reduce weight, each tread has a polystyrene former inside.

At first we left the treads unfinished, but found the bare concrete, though smooth, was prone to marking, so in the end we did apply a sealant.”
The stairs appear to be hung from stylish vertical steel rods, though they are mainly cleated to the walls of the stairwell. “The rods, apart from looking good, actually stop the stairs from swaying,” says Soronnadi.

Having considered ready-made precast units for the other staircase, the decision was made to make it from in-situ concrete. “After discussion with the contractor we felt that there was so much in-situ concrete being made in the area, we might as well add this,” says Soronnadi. “It also meant that we could fit it more efficiently into the exact shape of the site at this point.”

Again the concrete is smooth and consistent: “It came out beautifully, all except the tops of the treads which, being at the top of the mould, are always the hardest bit to get right,” admits Soronnadi. “We ground down any lumps and then painted these to prevent marking or dust issues.”

Both logistically and in terms of the programme, says Soronnadi, the shallower bore holes proved convenient, especially for such a restricted site. Standing in the basement exhibition area, and looking up through the full-height atrium, the building’s structure is clear to see. On the lift core, the lines of the 1,220mm x 2,440mm phenolic film-faced birch ply sheets that formed it are clearly visible, and have been carefully centred around the two lift doors. Tie-bolt holes are symmetrical, aligned and plugged with recessed biscuits made in Germany to match the in-situ concrete.

The board markings on the concrete soffits of the upper floors are also visible, and run in two directions, reflecting the 37° angle of the V-shaped plan. The exact position of each board was specified in the drawings to avoid an unseemly mish-mash where the two courses connect. The result is a final neat triangle at the centre of the V.

Perhaps surprisingly, given the smooth, pale finish of the walls and soffits, standard C40-50 visual concrete was used throughout. The mix sourced from a nearby Hanson batching plant was naturally pale in colour, allowing the building to make the most of natural light spreading throughout the floors via the atrium. The mix also came with an Excellent rating under the BES 6001 certification for sustainable sourcing.

“Getting concrete from only two miles away was obviously better environmentally, but also helped reliability,” says Sorrandi. “We knew exactly when deliveries would arrive, which helped the contractor to organise pours efficiently. We didn’t need trucks queuing outside – not that there was room for that anyway.” Close coordination of deliveries also helped reduce day joints, with fresh concrete ready to be poured as soon as the first batch had been vibrated.

The high quality of the concrete work can be seen on the round columns. These were made using phenolic film-lined cardboard forms encased with stainless steel outer covers. The result is desirably smooth and neat, though here and there the odd blow hole is visible. “We filled a few on the ground floor,” admits Soronnadi, “but a few small neat holes on the upper floors have been left as they give a sense of how the building has been made.”

The 500mm-diameter columns are few and far between – only three per floor – and while this does provide for enviably open, flexible spaces, it also means that the slabs have to span up to 12m. “To enable them to do this we have concealed [in-situ] upstand beams in the floor voids,” says Sorranadi. “So while the slab is only 250mm thick, there are additional upstands of another 450mm where needed.”

Cast-in conduits had to be designed into the slabs at an early stage to allow for lighting cables: “While the ground floor has exposed services in places, elsewhere we wanted clutter-free soffits. Some services could be concealed behind the acoustic rafts, but the lighting is a special feature so the cable routes were cast in.”

While he is speaking, design director Ratna has wandered over to play with the interactive touch screen in reception. The IOP, it seems, has got what it wanted: a stylish, sustainable building that is also engaging and fun.

Downstand solution

The exposed concrete soffit of the basement-located auditorium in the IOP is unique in that it features downstand beams to enable the slabs to span more than 11m.

To use the same kind of upstand beams as in the upper floors would have resulted either in the ground floor being above pavement level, or the auditorium ceiling being too low, explains project architect Soronnadi: “So to achieve the desired 3.6m ceiling height down here, we have used wider, shallower and heavily reinforced beams.”

He originally thought of this as a problem, he says, “but in fact, these 1,000mm x 200mm downstands are ideal for an auditorium as they help break up acoustic reflections. The grey fabric acoustic rafts fit neatly between the downstands and they’ve ended up looking really good.”

A peculiarity of the auditorium is that it extends beyond the ground-level footprint of the building and borrows space from under the pavement outside. This meant that the load of the building’s front facade lands some way inside the auditorium and so four substantial concrete columns have been positioned to deal with this. These rectangular, 500mm x 350mm columns were constructed with regular ply shuttering and, being located towards the back of the auditorium, do not obstruct the audience’s view.

PROJECT TEAM
Architect TateHindle
Structural and M&E engineer AECOM
Main contractor J Murphy & Sons
Concrete frame contractor Addingtons
Precast concrete supplier Evans Concrete Products

Photos Dirk Lindner