Embracing larch and spruce both in its structure and frame, Brent Cross Pavilion was the first building constructed in the new 180-acre Brent Cross Town development.
Aiming to create a flourishing ‘park town’, real estate developer Related Argent – in partnership with Barnet Council – pledged to create 6,700 new homes amidst 50 acres of green space. The visitor’s pavilion – which includes exhibition, work and events spaces, all served by a public café – was designed by Moxon Architects to communicate the vision of the development – and to act as a welcoming gateway to the local community.
Their design makes use of internally exposed CLT and glulam to create a calm and relaxed atmosphere for visitors to enjoy a coffee or explore the emerging development through showrooms and models. Externally, the structure is complemented by larch cladding and solid larch fins on the first-floor façade, along with a bespoke gabion veneer cladding below.
“The building needed to be a showcase,” explains Tim Murray, Moxon’s director, “but it was also important that it wasn’t simply a marketing suite: it needed to show the development, but mostly it needed to be a flexible building with real community use and access.”
The predominant use of timber as a structural, finishing and weathering material supported the development’s pledge to achieve net zero carbon by 2030, sequestering carbon in the structure and enabling an efficient construction.
The building was designed for both long term durability and future repurposing – enabling the adaptation of the structure for alternative uses and the ability to dismantle and reuse materials. Principles of circular economy governed the design and specification process, with offsite manufacturing minimising waste and the incorporation of recycled material into the substructure and envelope.
Straddling present and future contexts
Key considerations were that the pavilion needed to be low-carbon, flexible and demountable: and that it should create a sense of community from early on in the construction. Located at the tip of a green park, close to an existing parade of shops and houses, it was important that the building be considered from its various approaches and within its changing context – as the wider development progresses.
Amidst lush planting and landscaping, the exterior grid of solid larch fins encases large windows and lightly stained larch cladding on the first floor, while the upper storey is clad in zinc. A balcony on the first floor and an open-air terrace on the top floor give visitors wide views out over the newly landscaped park.
Inside, naturally finished timber surfaces create a welcoming environment. The walls of the double height exhibition space are neatly lined with large spruce panels, concealing services within the walls. The ceiling is lined with recycled composite woodwool panels that provide acoustic absorption. Large, glazed walls create continuity between inside and out, framing views of the park.
Murray explains that the flexibility of the inside layout was crucial as, although it would initially be used as an exhibition centre, it was unknown what kind of future facilities it might be providing. It was important to the client that this central ground floor space feel open to the rest of the building. The design team therefore worked hard with fire engineers to develop a strategy that would enable an open staircase, connecting the ground and upper floors. This, notes Murray, was quite a learning curve: “with only one staircase in a timber building, it was hard to do – but we showed that it is achievable!”
A mass timber superstructure
Civil and structural engineers Expedition worked closely with specialist timber subcontractor Xylotek to develop an economic and high-quality structural design for the pavilion. Ramboll UK, who were appointed at RIBA Stages 4 and 5, developed their specification and earlystage design into the finalised building.
The superstructure of the building is 99% timber, relying on CLT panels and glulam beams and columns for support, with minimal steel cross bracing for sheer load. As well as offering a lower embodied carbon footprint compared with more traditional construction materials such as steel or concrete, the use of mass timber entailed a faster construction time and reduced waste output.
Timber also naturally lends itself to being demountable as the connections are typically bolted and screwed, which can be dismantled relatively easily. As the majority of the structural timber was to be left exposed, particular care and attention was paid to the detailing and finishing of the structural connections.
Design issues to overcome
With 12-metre-long timber elements spanning the main exhibition space, supporting show flats located above, dynamics were a key issue. Detailed analysis considering the composite action of the first-floor beams and floor planks, and the form of the supported structure above, had to be undertaken to demonstrate the validity of the proposed solution.
The light-weight nature of CLT construction can also be susceptible to vibrations if the structural spans are long. A vibration criterion was defined using specialist analysis based on the usage of the space to achieve a level of vibration satisfactory to the client.
To minimise weight over transfer elements, the second-floor level is formed from lightweight timber SIPs with metal web joists spanning over, supporting the green roof above.
Due to the history of the site, the ground on the building plot contained a thick layer of fill which made shallow foundations unsuitable – even for this relatively modest building. Reusable screw piles were investigated but were likewise unfeasible for the scheme, so concrete piles were employed.
With specialist experience in CLT construction, RED Construction Group were appointed to deliver the visitor pavilion. Flat-bed articulated trailers delivered the timber to site in a just-in-time sequence. It was then stored in a large pile mat storage zone, where it was kept off the floor on substantial timber bites (which were donated to a secondary school in Hereford after use).
One of the complications that arose during construction was fitting the curtain walling system, as it required a much tighter tolerance (2 mm) than the CLT. A skilled carpentry company were employed to create bespoke picture frame packers to enable the curtain walling to be fixed directly onto the CLT structure.
Another area that was aided by the contractor’s experience with CLT was in justifying their fire strategy to Building Controls third party checkers. This was done in liasion with Swiss fire safety specialists Ignis Consulting, who assisted in developing EU fire regulations for mass timber buildings.
Success against the odds
Much of the design and construction of the pavilion was undertaken during the major COVID outbreaks and lockdowns. The need to adapt working practices required a closely coordinated collaborative effort across parties. Despite this impact, the project was able to be delivered on schedule, within budget, and meeting all the client’s requirements.
“So far,” Murray says, “it’s been really well received by the local community and used not just as exhibition space but also rented out for workshops.”
This article is taken from issue 4 of Designing Timber magazine.