Innovative engineering and craftsmanship elicit the age-old beauty of wood
Architects’ timber design skills seem neatly arranged into two categories: engineering and craftsmanship. On the one hand, timber has become a vehicle for displays of engineering prowess that deliver efficient, lightweight, quickly erected structures with minimal environmental impact. In another universe, we have architects concerned with the subtleties and nuances of different types of wood or their colour and grain, maybe their tactile and olfactory qualities, as well as the way they have been used in the past, and in some cases their relationship with the human psyche or even the material’s soul. But that would be a gross simplification.
It is customary for architects to speak of the beauty of wood as self-evident, sometimes referring to research that suggests people feel comfortable with this material without really saying why. It is questionable that surveys are always reliable generators of good architecture, although axiomatic statements often reflect sound intuitive judgements which are perhaps OK where design thinking has no sociopolitical impact. It would, however, be good to see more analysis of the psychological impact of wood asking, for example, whether too much can be oppressive. With regard to wood’s environmental qualities, Austin Williams has noted that research indicates that 32 per cent of UK architecture students consider timber the most sustainable construction material, whereas in China 30 per cent say it is the least sustainable (AR October 2015).
The Exbury Egg
Source: Nigel Ridgen
Case study: Atelier PRO, Klinker Cultural Centre, Winschoten, Netherlands (2015)
Klinker Cultural Centre Atelier PRO
Klinker Centre Detail
Comprising a theatre, library, arts centre, cinema, radio studio and café, the Klinker Cultural Centre has a foyer at its heart, a place where visitors meet informally and audiences join post-show discussions. The inner wall of this foyer, which encloses the auditorium and is untouched by intermediate floors, is clad in shingles of Basralocus, a timber species originating in Suriname used for Dutch canal and river bollards. Atelier PRO wanted to clad the auditorium with recycled bollards, but the contractor did not follow this up at the construction stage. The wood is so dense that preservative and fire-resistant treatment was not required. The tactile qualities of the shingles were intended to emphasise the central role of the auditorium within a building designed to accommodate small-scale spaces which integrate with the urban fabric, and they work in conjunction with the wall build-up to prevent noise break-out between spaces and regulate the foyer’s room acoustics, diffusing sound generated by activities such as live music.
The designers of Arup Associates’ BSkyB Believe in Better Building, an exemplar of engineered timber construction, emphasise the way its users respond to its surface finishes. Conversely, great craftsman-architects such as Shigeru Ban, as well as mastering timber’s expressive potential, can also reveal extraordinary technical trade secrets. To use an Israeli phrase, bluntly translated from the Hebrew, they can show us where the fish pisses.
Shigeru Ban subtly avoided the disastrous consequences of locking together the cedar members in the walls of a residence in Yamanashi Prefecture with alternating sliding connections. As Bob Maguire once said, timber doesn’t behave like cheese.
Case study: Arup Associates, BSkyB Believe in Better Building, Osterley, London, england (2014)
BskyB Arup Associates
Britain’s tallest open-plan timber building of its type houses Sky’s training/development suite, offices, and careers lab and is a venue for community events and school visits. Registered as ‘carbon neutral’, Sky targeted a 15 per cent reduction in embodied CO2 emissions and Arup Associates demonstrated that its proposed glulam frame and CLT cores outperformed steel, concrete or a hybrid of both and could achieve lightweight construction, openness and transparency. Only a timber frame – unheard of in a UK building of this type – could achieve zero embodied CO2 emissions.
Construction of the timber structural frame was considered 30 per cent faster than the alternative of reinforced concrete. Timber construction minimised noise, an essential consideration with an office building next door and, although specialist contractor B & K Structures resisted ad hoc carving on site, timber frames allowed more flexibility in the design and installation of follow-on trades, which involved working with screwdrivers rather than cast-in channels.
With an eight-week design window and only four between the concept and scheme stages, Arup Associates also built flexibility into the structure by designing arrays of penetrations in the beams which electrical services could be routed through when required. To provide an open-plan floorplate, structural walls are limited to stair cores, lifts and divisions between plant and public spaces. This is unusual for a multi-storey timber building, in which stability is usually provided by numerous load-bearing walls or stability cores with steel bracing or concrete walls.
Wood technology was also used for the floor and external cladding cassettes, which are aluminium-clad, as well as the stair treads and risers, with surfaces defined by stacked edges of thin timber laminate. Strip glazing, comprising stacked units, and external louvres had to come from a UK timber window supplier as it could ship them to site in three weeks.
At the frontiers of engineered timber technology, dRMM’s Sky Health and Fitness Centre in Osterley, London (2015), uses 4.5 tonne ‘superbeams’ developed by Arup and glued laminated bifurcated timber columns. Engineered timber construction, with cross-laminated timber (CLT) perimeter walls and floors, enabled this project to be designed and completed in 17 months and its superstructure was erected in 26 days, although its architects also emphasise the rich texture and beauty of its exposed frame.
In contrast to dRMM’s holistic use of engineered timber, Robin Snell and Partners’ Lower Vicar’s Barn Studio in Oxfordshire, completed in December 2014, contrasts new construction in English oak with the retained 1730 oak structure. Original internal wall and roof studwork was replaced in softwood in the 1980s. Now these additions have been replaced by flush fitting and finely crafted panels with hand-selected oak veneers laid randomly to minimise patterning effects. These have solid oak edgings and are applied to fully balanced plywood panels, 18mm thick for soffits and 25mm for walls, hung with split battens.
BIG Gammel Hellerup
Source: Rasmus Hjortshøj
Shigeru Ban Architects, Solid Cedar House, Kobuchizawa, Yamanashi Prefecture, Japan (2015)
Shigeru ban cedar house
The Solid Cedar House continues Ban’s previous elaboration of concepts explored by Mies van der Rohe involving brick and concrete partitions and interconnected sequences of spaces progressing from the interior to surrounding landscape.
In the Kobuchizawa project, solid cedar walls and slabs cut a variety of views from each room and conceal the neighbouring house and road. ‘Settlement of walls due to shrinkage and compression is unavoidable when building horizontally stacked log houses’, says Ban. ‘Even with additional built-in clearances, fittings such as doors and furniture do not function properly over time.’
Shigeru Ban Detail Section
As a countermeasure, the 120 x 120mm logs were mechanically dried in a controlled environment to reduce the moisture content to below 20 per cent. ‘Paneriido, 160mm panel screws, were used as a countermeasure against shear stresses between stacked logs’, he explains. ‘These were driven into the logs in two rows, at an alternating pitch of 120mm, so even where shrinkage and compression occurs, the logs move independently of each other, leaving the wall intact: horizontal gaps between logs may eventually appear, but these would only be about 1.5mm wide.’ To strengthen the walls against wind pressure, the stacked logs were reinforced with 36mm-diameter vertical steel rods cantilevered from reinforced-concrete foundations at 600mm centres.
Why cedar? No mystery: this was a client preference and the construction company favoured a local variety, available at low cost.
New walls at Lower Vicar’s Barn Studio, and also the oak floors, have bronze panels to protect them from open log fires, and their surface spread of flames treatment was chosen for minimal visible effect. Surfaces were left to wear naturally to maintain the oak’s original colour and match the Georgian frame. The new panels were laboriously set out to express the modularity of the oak room, and shadow gaps at junctions with original columns provide tolerance for, and emphasise, these members. New additions and bespoke furniture, using ancient techniques, combine with original construction to create an integrated whole.
Unlike Robin Snell and Partners’ oak casket, recent full-blown engineered timber projects invariably have something of the lumber yard about them unless – as in the case of BIG’s Gammel Hellerup High School in Copenhagen, where the sports hall beam curvature was generated by the trajectory of handballs – they successfully play off wood against other materials. Although their engineering prowess, neat construction logic and lack of inhibition can be an inspiration, they often struggle to touch the heart, especially if one prefers timber without knots.
Foster + Partners, Canary Wharf Crossrail, London, England (2015)
Foster Canary Wharf Crossrail
Foster Canary Wharf Detail
The mixed-use development above and around this Crossrail station has a barrel-vaulted diagrid roof angled off at prow and stern. Here alone, four of the diagrid’s straight, though in some locations tapered, European spruce glulam beams have been pressed to form two curved members at each extremity and also here, as Foster + Partners’ Jonathan Rabagliati explains, the gentle algorithm of their modules accelerates.
The diagonal glulam beams, some in tension and others in compression, were conceived with twists which tracked the roof’s surface geometry, but a good approximation to this form was achieved with straight members. These work with welded and galvanised steel nodal connections which control their twisting layout and axial rotations. About half of the 564 nodes are unique. Production by Austrian glulam specialist WIEHAG was almost fully automated. Although the nodes are not adjustable, the roof, whose components were precisely set out by jig, is within 5mm of its 300m notional length.