A rainbow-scaled facade not only updates a Victorian building’s insulation levels, it sets a contemporary note
With its rainbow glass brise soleil, there’s no missing the new addition to Swansea’s former central library, now occupied by the University of Wales Trinity Saint David. Powell Dobson Architects worked with facade engineer D2e to devise the bespoke, double-skinned facade for the extension, which provides passively ventilated and flexible studio space for product and automotive design students.
Rising 13.3m, the twin facade is the showpiece of an £15m refurbishment and extension of the 1887 building, which included a first floor gallery and basement workshops as well as the library. What was then Swansea Metropolitan University had occupied part of the grade II-listed building for decades and the management team saw an opportunity to do far more than simply gain extra accommodation when the library left the premises. As well as creating new light-filled and energy-efficient studios, the refurbishment improved accessibility through a new entrance while revealing more of the original building and creating a prominent presence for the university on the street.
Powell Dobson swiftly identified the corner site of Alexandra Road and Pleasant Street as the only viable location for any new build, removing two extensions from the 1930s and 60s that were particularly poor in terms of thermal efficiency. These were replaced with thermally superior new accommodation in the form of a new entrance on the corner and studio space stretching 38m back down Pleasant Street.
‘Our approach was to come up with something as passive as possible given the constraints of the listed building. We had to be creative about introducing cross ventilation and dealing with constraints such as the busy roads and solar gain on the south facing facade,’ said project architect Yvonne Gibbs, adding that a key objective was creating a clear contrast between the heavy masonry of the original and the lean, engineered aesthetic of the new.
The idea was for the double-skinned facade to provide a buffer for heat, light and noise, admitting fresh air without noise pollution and controlling the temperature by providing thermal insulation and passive ventilation when needed. The outer skin would also protect the brises soleils that deals with glare and allow the inner windows to be opened securely.
However specifying such a system with the required transparency proved easier said than done. ‘We looked at various systems for double-skinned facades but a lot of them were designed for applications which were more efficient for use on massive buildings,’ said Gibbs.
A particular issue was the lack of transparency when viewed at an oblique angle, due to the relatively deep mullions.
So the architect brought in facade engineer D2e to devise a bespoke solution. Managing director Dave Tyson came up with the idea of using a structural system of Vierendeels within the 900mm cavity between the two skins, so the outer one could be used without any mullions. The whole ensemble was installed by glazing subcontractor System Glaze.
AluK SL60 curtain walling system, with 150mm deep mullions, forms the inner skin of the facade, and is connected back to the structural frame at the floor slabs. The outer skin is of structurally-bonded, toughened, laminated glass, hung from the roof.
Bespoke aluminium Vierendeels link the two skins, acting as horizontal beams between the main building columns behind the twin wall and forming walkways at ground and first floor level within the interstitial space. At the back they take vertical support from the main structure at the floor positions. At the front, they take vertical support from pairs of stainless steel rods hung from the roof in tension. Horizontal wind loads are transferred from the outer glass panes to the Vierendeels above and below the glass via a small extruded aluminium bead that is structurally bonded to the top and bottom of each pane. The rods also hold the brise soleils.
‘It was a interesting collaboration whereby Dave Tyson from D2e progressed the engineering ideas while I modelled the facade in 3D. The two processes evolved and informed one another to achieve the most transparent solution possible,’ said Gibbs.
Overall, the aim was to minimise peak heat and cooling loads. The facade can perform in different ways according to the season, with banks of bespoke open-in AluK 58BW windows on the internal wall regulated by sensors on the curtain walling and opening and closing automatically depending on the weather. The twin wall intake vents are at the base of the facade and extract vents are in the parapet. In winter, solar gain provides a thermal buffer that effectively acts as a blanket, reducing the heating load. In spring and autumn, the vents are more open to draw heated air through the interstitial space into the extension and then out through high level vents within the lift core riser and new rear stair. In summer, when the interstitial space becomes quite hot, warm air is extracted via vents in the outer facade as cooling air is drawn through from the basement. At night, this can be used to cool the floor slab.
‘The facade buffers light, air, heat and noise throughout the seasons, and constantly adjusts to create a conformable internal climate. In terms of insulation, it uses solar gain to minimise internal heating load,’ says Gibbs.
The brises soleils were an opportunity to signal the creative activities within the buildings, and in particular those of the glass school, which had occupied it for some time. The architect chose 10mm, sandblasted low-iron glass blades which are connected to the rods that link the two layers using fixings designed by D2e. These blades were treated with a durable nanotechnology coating created by Rodney Bender of Innovative Glass Products in various hues to give the colour transitions required across the facade. This gives different effects of transparency and opacity depending on light conditions.
Access to the interstitial zone is via AluK GT55 NI doors on each floor.
At the entrance on the corner of Alexander Road there was no need for a double-skin facade, so an 11m by 11m structurally glazed glass assembly was used, running the full height of the building and giving maximum views of the newly-exposed original side wall, which hadn’t been visible for decades. Above the entrance a cantilevered roof with aluminium soffit extends dynamically towards the corner to establish a visual marker that heralds both the new way in and the creative activity inside.
Completed last November, the extended and refurbished building is seen as part of an ongoing renaissance of Swansea’s historic arts quarter. The ornate, circular library reading room at the heart of the building has been restored and will be used as a public venue.
Client University of Wales Trinity Saint David
Architect Powell Dobson Architects
Structural engineer CB3
Facade engineer D2e
M&E engineer Intentium SL
Glazing sub-contractor System Glaze
Contractor Andrew Scott