There can surely be no more obvious location for a building designed to show the use of timber than a botanical garden, the outdoor exhibition environment for a whole host of native and exotic plant species.
Edinburgh’s Royal Botanic Gardens has stepped up to the plate on this not once, but twice, with a pair of visitor centre/gateway buildings that demonstrate quite different approaches to designing with timber.
The first of these is not actually in Edinburgh itself. The Royal Botanic Gardens has an outpost at Dawyck, near Peebles in the Scottish Borders – and a hidden gem it is too.
The gardens there have a very distinctive micro-climate that has facilitated the growth of all sorts of unusual plants and trees, but until recently had only a glorified potting shed as its entrance portal and tearoom. That situation was altered by the relatively recent construction of a new shop, café, and ticket office designed by Simpson and Brown Architects, a practice with a long history of timber usage (for example at the Scottish Seabird Centre at North Berwick, the Scottish Ornithologists Club at Aberlady in East Lothian, the ticket office to the Seahouses in Northumberland and the forthcoming Burns Museum at Alloway).
Being originally conservation oriented, Simpson and Brown have a predilection towards the use of green
timber and the new £1.6m gateway building at Dawyck is no different, with its simple post and beam structure in green oak.
The most recent manifestation of the Royal Botanic Gardens interest in timber architecture is to be found on the west side of its Edinburgh headquarters location, however – the £16m John Hope Gateway Visitor Centre – and replaces a collection of large scale but inadequate sheds that previously housed the main shop and plant sale centre. The just completed building is a considerably enlarged enterprise, containing a new exhibition space, a demonstration area with satellite links to scientists in the field, a restaurant, bar, VIP room and shop.
Designed by Edward Cullinan Architects and engineers Buro Happold, the 2,750m2 facility is a world away from the simple shed, or even the waney-edged treehouse aesthetic that many people seem to associate with gardens. This, by contrast, is an exemplar of timber engineering with glulam, cross-laminated timber and hybrid steel and timber structural elements, finished externally with home-grown larch cladding vertically-fixed over its three storey height.
On approach, however, the most obvious feature of the building is the roof, a ‘floating’ canopy of cross-laminated timber planks supported on an 8x6m diagonal grid of 5m-long and unusually-shaped glulam beams. These in turn are supported on a grid of rolled steel cruciform columns set on concrete pad foundations. The columns narrow towards their top and have a series of steel flitch plates welded to a vertical steel rod that forms the columns ’capital’.
The rod is used to transfer the roof loads from the glulam beams which, with their circular pattern of bolt connections, provide a distinctive engineered contrast to the natural impression conveyed by the timber itself. These connections are critical to the building’s structural design, since otherwise the differing tolerances required between the timber and steel would have been extremely difficult to resolve. The flitch plates are embedded in a deep vertical slot in each of the four glulam beams that meet at the column heads with a similar, smaller plate connecting the glulam beams at the centre of the diagrid spans.
And it this arrangement of the beams that is the key to the building’s structure and planning, with their depths
tapering from 1035mm at the column heads to just 300mm where their tips meet. The result is a series of coffered bays that are not only used to define the internal spatial arrangements but whose exposed form is visible through the double height glazed entrance lobby and throughout the building itself.
As already mentioned, the use of engineered timber does not stop with the structural grid, since cross-laminated timber planks supplied by KLH are also used to provide the first floor and roof to the building as well as its internal walls and balustrades. The exposed planks form the soffits and are coated with a white stain to reflect as much light internally as possible that enters via a series of transparent ETFE panels that span the length of the internal atrium. It would be fair to say that, despite extensive interest in the product from architects, Scotland is still pioneering territory for exponents of cross-laminated timber and the Royal Botanic Gardens Visitor Centre is the first really substantial example of its use north of the border.
The engineered timber piece de resistance for most people, however, will be the spiral stair that connects
the ground floor atrium space with the upper level. The bespoke laminated form gives a beautiful sculptural
dimension to the space which, once stepped upon, can only be described as a kinetic experience, the natural spring within its structure sure to provoke whoops and hollers from its users.
The other very obvious use of timber on the building is the external cladding where the Scotlarch brand European larch planks from Russwood have been fixed vertically, board-on-board, in alternating directions. Already weathering to a silver grey colour, this looks to be something of a case study in cladding orientation, with the boards whose main faces are set towards south-west more evenly responding to UV degradation than those set to the north-west. Eventually the differences will disappear and an overall pale grey should tonally respond to the Caithness slate of the main stair tower.
Staff moved into the building during August, but we must wait for the sedum roof and the biodiversity garden to the rear to mature before a grand opening takes place next year. Only then will its many delights be revealed to the Gardens’ loyal public.
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The circular pattern of the bolt connections provides a distinctive engineered contrast to the grain of the timber |
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The staircase provides a 'kinetic' experience |
