Review for Architecture Today: Invisible Studio’s two new buildings for Westonbirt Arboretum are tucked away in the back, in the ‘working’ part of the estate. A machinery shed and a mess room for paid and volunteer workers, the brief for the buildings was functional and the budgets modest.
The two buildings were designed alongside one another following a competitive tender process, and built with a traditional contract and main contractor. The tiny mess room evolved into a more overtly ambitious small building, while the machinery shed reserved its invention for the construction rather than the form of the building. These two buildings are an exploration of the architectural use of home-grown timber, both achieving much with little. That they are here at all (experimental timber buildings on a working estate?) is something of a surprise, and part of wider improvements by the National Arboretum.
The estate was largely created by wealthy landowner Robert Holford, whose vast inherited family fortune was made selling fresh water through a canal to London. Holford set about creating an extensive landscape around his re-modelled house, adding specimen and exotic trees, indigenous woods as well as collecting orchids and shrubs from around the world. Three generations of the family continued extending the arboretum so that when the Forestry Commission took over the estate in 1956 there were 600 acres of grounds with 17 miles of paths. The estate and grounds are Grade 1 listed; the Arboretum nationally important with 120 ‘champion trees’ (the tallest or largest of the species in the UK).
The Arboretum now attracts 350,000 visitors a year, and has recently been through a re-vamp to accommodate the increasing numbers of visitors, with a new Welcome Building and Treetop walk, both designed by Glenn Howells Architects. The Welcome Building- opened in 2014- is a gently curving timber building that divides the grounds from the car park, and acts as barrier as well as a gateway to the estate. It’s a neat unassertive modern building designed to protect incursion into the listed landscape. It’s inevitable that with this many visitors the original quality of the landscape will be altered, and that the quantity of resin-bound gravel will increase with more people wanting to get between toilets, ticket office, and a restaurant some way into the park. This is a popular place, with a very active volunteer force assisting the permanent staff in managing the grounds, and a 22,000 strong Friend’s group. The ‘offer’ has recently been increased with the addition of a treetop walk, which bridges a small valley and allows access to an area previously considered less accessible.
The Stihl Treetop Walkway snakes its way from close to the Welcome Building across the valley and threads its way to land 300 metres away in the woods. It’s an elegant structure, gently sinuous, with canted striding legs that suggest movement and play, and restrained enough not to dominate the trees. It slopes gradually and expands out to create viewpoints and transports the visitor through the canopies. Oddly the containment within the narrow pathway in such a vast landscape has the opposite effect of the anticipated vertiginous thrill, akin to suffering a narrow pathway full of people from the cliff-top car park in order to get down to the beach. Personally I would prefer my arboretum experience to be with more trees and less people, but concede that there are many that even having got to the beach prefer crowds to open spaces. Undoubtedly the buildings will do much to make the arboretum a destination, broaden the appeal of a visit and hopefully encourage a wider exploration.
These changes were brought about by ex-Curator Simon Toomer, a forester with a broad and persuasive vision for continued change and renewal, who over a decade made changes in forest management, including selective felling and the creation of new walks. Under Toomer’s guidance Invisible Studio were chosen on a platform of invention, collective action and education to design the machinery shed and mess buildings.
Piers Taylor teamed up with long-term collaborator Charlie Brentnall, of Carpenter Oak, who also worked with Taylor on a similar pair of buildings for the AA Design & Make programme at Hooke Park. Their proposal involved working with volunteers on the buildings, and using only timber felled at the Arboretum. The building was part-funded by a £600,000 grant from the Wolfson Foundation (the remainder raised mostly through donation), and the educational and research aspect of the proposal fulfilled some of the criteria for the funding. Teams of volunteers worked on the construction, and students organised through the Carpenters Fellowship worked with Brentnall on the traditional framing of the large barn. The strategies for the two buildings evolved through exploration of the timber that the estate had to work with; green larch, oak trees felled four years previously, and Corsican pines felled specifically for the building.
Early design sketches for the big shed show the large 20m span formed from a curved Belfast truss, or later trussed portals. But the discovery of the possibility of being able to use single 20m lengths of pine, and the realisation that a simpler truss would be £100,000 less expensive prompted Taylor and Brentnall to change tack. Brentnall has been framing timber for 30 years, and firmly plants himself in a tradition of construction centuries old. The resulting kingpost truss is both straightforward and impressive; it is likely that these are the largest single lengths of structural timber in the UK, at least, the pair have yet to find another longer. The timbers were worked by hand on site in an act that connects this building to a long history of timber building. The large size – together with the lightweight roof, which has no weight to resist uplift- has required joints to be designed by engineers Buro Happold rather than a reliance on traditional framing methods. The resulting joints look slightly odd; the steel is present but not expressed, so that the traditional timber housing looks as if something is missing. The cladding makes use of the rest of the tree; after the structural sections were cut the rest of the section was milled to make the varying sections set vertically with air gaps between. But this building really is about the roof, and the sides are allowed to open fully with industrial segmented doors on both sides, so that the large covered space opens to yards on both sides. The tree team told Taylor that for this building they didn’t want ‘any arty-farty nonsense’, and the building is anything but. It feels like a timeless space, and delightfully free from affectation.
The Mess Building sits in contrast to the Machinery Shed, and is designed to be a playful presence in the back yard. This is a conscious elevation from an ordinary building, and reflects the engagement of upwards of 30 volunteers working alongside the permanent tree team. Built with a traditional contract but with volunteer labour, the details are sometimes unevenly applied, and perhaps there was simply too much for one little building to take on. But the fact that Taylor pushed hard for a small budget building to deliver more than one might expect is all to the good- this is a building that will lift the spirits after a long day in the woods.
The north entry is via a low overhang, and accessed from a simple ramp from the yard, whilst the south facing elevation rises up to suggest a chapel in a wood. It’s caught between a humble house-in-the-woods and something less familiar. Inside, the space is a far remove from the kind of community meeting room that might usually serve the purpose. This space would make the volunteers feel especially valued. In terms of its construction, on the one hand the building is straightforward, with larch studs, oak joists, plywood lining, and oak board cladding. But Taylor has tweaked the forms and subverted traditional details to make a building that is designed to be noticed. The oak cladding is left deliberately uneven- a sort of contemporary waney edge- making an art out of expedience, as to mill the boards straight would have added cost. This all-over cladding reaches the ground in a skirt; a hovering moth of a building, unsettling, and ready to take flight.