Centre stage

The theatre sits alongside Aylesbury's canal basin and is the centrepiece of the town's Waterside development

Recreating the hills and forests of the Chiltern countryside in the facade of Aylesbury Waterside Theatre required some precision timber engineering and a radical bespoke glazing solution, writes Stephen Cousins. Photographs by Tony Weller

When architect Norman Bragg was struggling to come up with a concept for the proposed Aylesbury Waterside theatre in Buckinghamshire, the last place he expected to find inspiration was driving down the A41 dual carriageway.

“i was heading towards Aylesbury to visit a possible site, when i noticed thousands of sleek dark pine trees covering the horizon, a really impressive sight,” explains Bragg. “then, as i approached the town through Aylesbury Vale i was awestruck by the beautiful, undulating green hills that dominate the scenery.” 

Taking the local chiltern landscape as his cue Bragg, who is now directing the theatre project for Arts team, part of RHWL architects, was able to start sketching his ideas.

Fast forward several years to the same Aylesbury site in December 2009 and these natural features can now be seen clearly in the building’s facade. the pine trees are represented by 106 structural glulam timbers, which stretch to the theatre’s roof and follow a curve around three sides of the building. the columns are spaced in a pattern intended to mirror the random scattering of trees in a forest, and stand on top of an undulating reinforced concrete base that will be clad in natural stone and a mosaic of pebbles.

Bringing nature to life in the building’s envelope has been the task of main contractor Willmott Dixon and german cladding contractor FinnForest merk. The facade forms part of the theatre’s structural timber frame, which supports two floor decks and the roof. introducing a natural unpredictability meant engineering each larch column as a unique fin shape, as well as hundreds of bespoke connection details where the columns meet the roof. And with the structural timber columns projecting outwards from the facade and taking up a lot of space, a bespoke “reverse” curtain walling system had to be developed to hang glazing from the backs of the columns.

Willmott Dixon’s project director, mark chamberlain FcioB, says he has never worked on a project like it. “the timber frame and facade is like a huge meccano set of loose-fix timber,” he says. “on site, it has felt like an endless series of tests to make sure things fitted together properly.”

Although only a two-minute walk from the centre of town, Aylesbury Waterside theatre is conspicuous to passing drivers on its site next to a roundabout on the ring road. it’s one of several cultural, retail, infrastructure and residential buildings planned as part of the aylesbury Waterside development, an urban regeneration project intended to transform a rundown area of the town. 

The £35m theatre, which has a 1200- seat auditorium, was commissioned by aylesbury Vale District council and replaces the civic theatre in the town.

The auditorium is housed inside a reinforced concrete block at the core of the building, which is surrounded on three sides by the timber and glass facade.

The space between the facade and the auditorium block functions as an acoustic buffer, keeping out traffic noise and at the same time providing light, spacious public areas and views of the adjacent exchange Street and uphill towards the town centre.

“A major concern was to get away from designing a characterless glass curtain-walled building, so we decided to make the timber columns the primary element on the facade,” says arts team’s Bragg. “using the concept of a forest as a starting point we tried to introduce unpredictablility into the design to mimic patterns in nature.”

Rather than a uniform grid, the columns are set out at 1.2m, 1.8m and 2.4m intervals to reflect the scattering of trees in a forest. the gradual curve in the plan also proved cost effective, as the glass curtain could be formed by faceted panels instead of more expensive curved glass. the height of the columns also changes where they meet the roof, which curves along the building’s length and also tilts away from the street. every column therefore had to be manufactured to a unique length, as John talbot mcioB, senior design co-ordinator at Willmott

Dixon explains: “Arts team produced a three-dimensional model of each column, the data from which FinnForest merk fed into its computerised cutting machine. Each has a flat interior profile, which the curtain walling system is attached to, and an elliptical curve cut into the exterior.” the original plan was to source all the wood locally, but this proved too costly and instead hard-wearing larch was sourced from sustainably-farmed forests in the czech Republic.

With such a large amount of bespoke engineering, Willmott Dixon was wary of tolerance issues between the timber frame and the glazing system, so it opted to combine the two into a single facade system. “if a pane of glass broke, for example, it would have been hard to identify which firm was responsible,” adds Talbot. Finn Forest merk emerged as the only company with the necessary expertise and track record in combining timber with glass.

The structural timber columns in the facade form the main support for a bespoke reverse double-glazed curtain walling system designed by FinnForest merk, which incorporates 610 glazing panels from german firm Raico. The system had to be designed to be fixed to the flat interior surfaces of the columns.

Between each pair of columns, there are five or six double-glazed panels, ranging from 1m to 2.5m high, stacked one on top of the other. these sit inside an aluminium carrier system, which is screwed back into the columns. An aluminium pressure plate strip lined with neoprene rubber is placed over the glass and screwed and jointed to the carrier system to create a watertight and airtight seal between glazing panels. the pressure plate is then concealed behind a larch timber casing (see diagram, previous page).

As there are only a few, irregularly distributed structural timber transoms on the facade, the system required cross-shaped steel plates bolted to the columns to carry the weight of the glass onto the columns. Larch brise soleil cut down solar gain and add a further horizontal element.

The curtain walling was designed to allow the installation and removal of glazing panels from inside and outside the building – necessary because when the building opens it will not always be possible to bring heavy lifting equipment inside. However, as each glazing panel is about 30mm wider than the space between the columns, removal from the outside would clearly present problems. the panels therefore had to allow twisting in a vertical plane to pull them out through the facade. this meant incorporating a 250mm gap between the internal side of the external timber columns and the internal floors to allow space for the twist. Here, the relatively low number of structural transoms made the system possible. the internal larch casings and external brise soleil shades can also be removed where necessary. 

The double-glazed curtain walling is a drained system designed to allow some water to penetrate at the edges of the outer layer of glass then drain away through the mullions, into the transoms and out of the building. at the base of the wall, water drains directly from the cavity into an L-shaped aluminium tray that directs the water out over the base plinth of the building.

The facade is now close to completion. All that remains is to clad the sprayed concrete layer at the base of the columns with a mosaic of dark pebbles and create the wall of cotswold stone cladding beneath. the theatre opens this summer, but its striking form is already holding up well against the natural drama of the surrounding landscape.