Kimbell Art Museum extension, Texas

There is an irony in having to build in the shadow of the Kimbell Art Museum, the 1972 masterpiece by Louis Kahn, a man fundamentally obsessed with light and shadow. But having built a mere stone’s throw from Le Corbusier’s chapel at Ronchamp only two years ago, it’s not a challenge that Renzo Piano shirked. Far from it; the original site for the extension – to the east of the gallery (effectively the building’s rear) and separated from it by a road – looked an unworkable proposition to Piano. So, aware that he had to respect both scale and proportion of Kahn’s primordial concrete and travertine vaulted lozenges, the architect successfully argued to build on the ‘Great Lawn’ to its west, part of Kahn’s ceremonial entrance and directly addressing the Kimbell’s principal facade. This almost confrontational approach has led to some oppositional formal moves that consciously counter point Kahn’s work, while manifesting a natural evolution of Piano’s own gallery oeuvre. And like the building it responds to, his $135m extension, which opened last December, puts all the magic above picture rail level.

At 7500m2, Piano’s pavilion doubles the area of Kahn’s original building and creates two new major ground floor galleries, with below grade auditorium, education, servicing, minor gallery and 135 parking spaces, largely housed beneath a green roof. Since its founding, with limited space, the Kimbell has always sold pieces in order to buy. Over the years, this has meant that although a provincial museum, the quality of works on display has only increased. The new gallery means the Kimbell can show most of this collection and also allows for state-of-the-art modern gallery spaces to host temporary shows and, with its 300 seat auditorium, associated events.

‘Even a room which must be dark needs at least a crack of light to know how dark it is,’ said Kahn. This thinking very much dictated his approach to the Kimbell, whose long, low concrete barrel vaults are each pierced length ways with a central slit, allowing their polished soffits to act like blotting paper and bleed light across their surface. The specular effect is sublime, and wholly suitable for Texas’ arid clime, but at around 75 lux it needed augmenting to 350 lux by artificial light to give the correct viewing conditions for art. With his new pavilion, Piano has circumvented this need for artificial light during the day by creating a space that, in a way, acts as a kind of Kimbell Art Gallery in negative. While the confluence of Kahn’s 7m wide barrel vaults are reflected with dual 1.5m deep timber glulam beams spanning the full 30m width of both galleries, Piano has inserted between them– instead of imposing curved concrete – a pure, diffused white light to create the antithesis of Kahn’s effect.

Renzo Piano Building Workshop partner Mark Carroll explains the lightweight roof system for the Kimbell as a development of the gallery spaces that they have worked on for the last 30 years – in particular the Menil Collection in Houston, Switzerland’s Beyeler and the High Museum in Atlanta. ‘The difference is that here there was no carte blanche; we needed to follow Kahn’s basic rules, but also to respond to them in our own way,’ he says. ‘With Kahn, the views are all internalised but our building is all about transparency and drawing as much light into the building as we could.’ The strategy has resulted in the formal massing of the building- effectively one storey, with full glazing to the north and south and 1.5m thick concrete cavity walls to the east and west. Between the two main galleries runs a large daylit lobby and reception space connecting the galleries to each other and the auditorium/archive/carpark level, allowing views east to the Kimbell. Above it all, delicately poised on spigots over those deep dual cross-laminated timber beams, runs Piano’s lightweight steel and glass roof structure, cantilevering out at its ends 3m over the pavilion’s external concrete columns. With 40m of clear space between the cavity walls and the columns, and filled with homogenous light, the galleries are a model of flexibility.

The roof here represents a sublimation of all the other gallery roofs that RPBW has designed, and responds to the need to optimise light quality and minimise resultant heat gain as part of a larger mechanical ventilation and sustainability strategy for the pavilion. ‘In Texas, light and heat need to be strictly controlled. Usually you would shade, then filter the light and add photovoltaics separately; here Piano has integrated all three functions into the one roofing system,’ explains Arup lighting designer Arfon Davies. The resulting sections are double glazed, krypton-filled, lower level curved panels, above which sits a louvred panel whose uppermost faces are impregnated photovoltaic cells. The louvre panel size is dictated by the glazed module below and keeping it to a size that a single person can open for maintenance.
 
He adds that the louvre panels operate independently of each other using mechanical worm drives to maintain tight control of light in the galleries: from flooding them with light down to almost blackout conditions for videos. Davies explains that the louvre system does not actively move to control the light throughout the day, however. This is mainly done by the frit and diaphanous fabric scrims running between beams below the level of their interstitial cross-braced members. And as Davies explains,  ‘Their usual 45 degree angle proves optimum conditions for the PV cells on the outer face, offsetting around 20% of the building’s carbon footprint through the PV installation and providing additional benefits.’

The low level displacement air conditioning strategy minimises direct light ingress so that temperatures can readily be held at a steady 72ºF with a relative humidity of 50% +/- 5%. Louvres also close to act as a security layer for the roof of the pavilion by night, and ,along with the shutters on the main glazed facades, control diurnal interior temperatures. They even protect against extremes of weather: namely the county’s notorious hailstorms. ‘The louvres can almost instantaneously be flipped to 180º in “hail mode”, protecting both the glass roof and the PV cells,’ he adds.

All the beams were pre-cambered at 9in to allow for the natural slump of the beam over its 40m length and additional dead loads from the roof structure itself. Externally, the subtle curve of the glazed panels directs water to an insulated aluminium gutter detail above every double beam. Internally, these beams carry hidden lighting tracks and sprinkler systems; this is the first gallery RPBW has lit using LEDs.

How successful the pavilion will be as an adjunct to Kahn’s timeless gallery only time will tell, but RPBW has at least partly played on its own terms. Carroll says that while Kahn’s structural bays and massing have been respected, it’s clear the two are grounded in different architectural approaches – one ontological, the other functional. ‘We followed the rules that we could. We were very keen that our building and Kahn’s were engaged in an ongoing dialogue,’ he concludes. This supposition should be no surprise as Piano apprenticed with Kahn from 1965-1970; but the resulting volumes facing each other across the Great Lawn – one drenched in homogeneous light, the other with it seeping through narrow slits – speak of a world now concerned more with apparent revelation than its darker recesses. 

AIR CARES

Although Becci Taylor was Arup project manager for the Piano extension she can’t help but talk about the air handling in Louis Kahn’s original museum. ‘I couldn’t work out where it was running – it turns out there’s no horizontal distribution at all at gallery level,’ she says. Instead, the Kimbell has a double basement with the plant room bang in the middle of level -1. ‘Only one piece of plant serves the whole building and it’s massive. All the ducts run down from it to level -2, it’s distributed horizontally there and then pops back up to ground within its 300mm concrete walls to serve the gallery. It’s quite intelligent as a services distribution strategy,’ she adds. 

Piano’s extension uses its east and west concrete cavity walls as part of the air handling strategy in its galleries, but here they’re extracting displacement air at high level. Taylor says most of the heat gain mitigation has already occurred due to the louvres shading the low-e glass roof panels, but as it draws exhaust air from the gallery it also takes any hotter stratified air lingering at the glazed ceiling soffit. 

The real genius is in the innovative floor of the column-free spaces that Arup developed with RPBW, says Taylor, as it was always about keeping the galleries free of service risers and obstructions. The team developed 400mm dual concrete slabs and 50mm sleepers above to create a void through which to run supply air. ‘Every 100mm plank has a 2.5mm gap to allow supply air to feed through evenly across the whole floor, creating a truly ‘breathing floor’, which we think is a world first,’ she says. This lets gallery spaces maintain a temperature of about 72ºF and relative humidity of +/-50%.

Taylor says there is also more than just one air handling system. ‘There are different plant systems zoned by use and location. The larger room deals with highly serviced spaces, like galleries and auditorium, but the smaller one deals with less demanding ancillary zones where things don’t need to be as controlled,’ she adds.