Duncan Baker-Brown on a working showcase for sustainable timber construction in Sussex. Photos: Paul Riddle.
Steven Johnson and his practice The Architecture Ensemble have recently completed the second phase of workshops at the Woodland Enterprise Centre at Flimwell, Sussex. Set among 50 acres of redundant coppice woodland, the project demonstrates the significance and real value of these often neglected resources on our doorstep.
Work at Flimwell dates back ten years when, following an invited competition, Woodland Enterprise Ltd (WEL) commissioned Fielden Clegg Bradley (now FCB Studios) to build the Woodland Enterprise Centre, phase one of a masterplan by Robert Rummey. WEL’s East Sussex manager David Saunders’ ambition was to promote good practice in woodland management and to prove that ‘low value’ small-section timber could be used, with minimal processing, as a high-grade material for joinery, cladding and timber frames, instead of simply post-and-rail fencing or charcoal. There are thousands of acres of ‘working’ woodlands in Kent and Sussex alone, mostly untouched since the mid-1980s when the bottom fell out of the coppiced timber industry.
FCB’s Woodland Enterprise Centre, with its gridshell vault of local sweet chestnut and Douglas-fir, houses WEL’s offices, among others, and the main space, though no longer a workshop, is rented out for events. While engineer Atelier One and FCB were developing their gridshell, a rather higher-profile version was being built elsewhere in Sussex, at the Weald & Downland Open Air Museum, by Edward Cullinan Architects with Richard Harris of Buro Happold. This project was run by Steven Johnson, an American architect and Architectural Association postgraduate. Something of a novice in timber construction, he soon developed a passion for timber, carpentry and indigenous woodlands. In particular Johnson was struck by the passion of carpenters: ‘They are often keen to do things differently and go off and research traditional or emerging techniques’. He also became aware of the importance of timber specification in terms of nurturing or harming natural environments.
Soon after the Flimwell gridshell was completed Saunders began to formulate ideas for a timber workshop that could serve small rural businesses. WEL had already obtained outline approval for eight B1 light industrial/ office units on the site, each 6 by 15 metres. The approval rather cleverly agreed the number of units but not the layout, which
allowed the scheme to be flexible and develop as tenants (and architects) were found. The gridshell served its purpose well but WEL’s mission to make timber construction and technologies accessible to anyone who was interested would be better served by small-scale exemplar buildings.
Around the same time, Steven Johnson approached WEL with the idea of developing speculative low-carbon B1 units in the Kent and Sussex area. The original design was for a series of glulam timber frames supporting prefabricated timber gridshell vaults. Johnson came with a ready-made design and build team – himself (now Architecture Ensemble), Buro Happold and The Green Oak Carpentry Company – essentially the Cullinan gridshell team. Over the next few months they developed ideas for four pairs of two-and-a-half storey units, designed so they could be opened up into double-size units if required. Units could be subdivided vertically by floor or kept as a single volume with an optional mezzanine. Occupants were handed shell-and-core units to fit out as they wanted, a significant selling point for the first wave of tenants.
Seeing how some of the tenants have carved up the beautiful interiors is something of a reality check. These are productive industrial places where function definitely rules over beauty, although at least one of the units has been occupied with sensitivity to the original vision. However, even the worst offender cannot detract from the beauty of the first-floor volume, where the two halves of the split cruck frames almost meet. The vertiginous tactile frame allows for maximum floor area with the potential first floor at least one-and-a-half storeys high.
Johnson’s interest in reinterpreting traditional Sussex timber vernacular construction, married with his commitment to using as few resources as possible, sat well with WEL’s philosophy. So in designing adaptable workshop units it was logical to work with a traditional timber frame, in this case with a ‘split’ cruck to allow for a continuous rooflight along the apex, providing natural light and, if required, ventilation.
FCB’s Woodland Enterprise Centre gridshell was an essay in the use of finger-jointed sweet chestnut, and WEL wanted the workshops to demonstrate the potential of other UK-sourced timbers, as well as new construction techniques emerging from continental Europe. In this, Flimwell’s approach differs fundamentally from that of purists such as Ben Law, who built his house entirely out of timber from his own woodland. Rather, WEL promotes the celebration of woodlands, their progressive sustainable management and their potential to supply a twenty-first century construction industry.
As the Flimwell project has evolved, Johnson and his colleagues found themselves able to build the workshops in pairs, and after each pair was completed they had time to reflect and refine their ideas before developing the next. So this example of practice-led research has the potential to become a contemporary version of the Weald & Downland Museum, especially when the third phase, Adventure Rope, is completed in December, and students will be able to learn rope skills on the building’s roof.
The first iteration of the workshops comprised a mechanically-laminated cruck frame constructed from sawn sections of green Douglas-fir (not indigenous but plentiful) and clad with prefabricated timber cassettes (also Douglas fir), filled with wool insulation and made locally by Inwood Developments. Both roof and walls are clad externally in Douglas-fir rainscreen boarding. External joinery is positioned at each end of the building and employs Accoya’s ‘pickled’ Radiata Pine. This product combines the abundance and lightness of the softwood with the durability of a hardwood such as teak (acquired through chemical impregnation, in this case acetic acid) – a clever re-appropriation of a cheap timber crop normally used for paper production. The workshop roofs overhang and, together with the split cruck frame and first-floor cladding panels (angled to test differing weathering effects), lend a distinctive contemporary industrial feel – perhaps northern European rather than rural England.
The second phase of building delivered four workshops that demonstrate a refinement on the first pair. The first batch picked up on the trend for prefabrication, but in practice this didn’t prove cost-effective (scaffolding impeded the fixing of cladding and there were problems with damage and fitting of panels). Half-cruck frames were craned into position over the scaffolding and the paired halves bolted together. The latest workshops retain the slimmed-down version of the cruck frames, but this time were assembled as complete crucks flat on the ground and lifted to vertical with a telehandler. However the cassettes were dropped in favour of solid cross-laminated structural spruce panels spanning five metres between frames. These loadbearing panels provide an internal finish as well as some thermal and acoustic mass. The panels, 110mm thick for the roofs and 90mm for the walls, were easily installed using the same telehandler as for the frame erection. They arrived in two full lorry loads from Germany and fitted perfectly.
All panels have 100 to 135mm of Gutex timber fibreboard screwed to the outer face that is again finished in Douglas-fir cladding. Johnson is happy to use cross-laminated structural panels in the creation of his hybrid timber structures and justifies importing the products because they demonstrate design innovation. He is also convinced that less material is used in this latest version.
The design changes implemented between each phase of the workshop buildings may be subtle but they are significant. The end results are aesthetically similar; it’s all in the detail. The last phase is yet to be commissioned and it will be interesting to see how Johnson and his team develop the design further in the light of their discussions regarding the viability of structure made entirely from cross-laminated panels, omiting the split cruck frame altogether.
Johnson’s concerns are not simply with timber construction techniques, and he will discuss with eloquence the qualities of sunlight and shadows, his preference for the uninterrupted horizontal timber boards that clad the second batch of workshops, the way the roof overhang creates shadows that affect the architectural language of the workshops, and the way the large windows engage with the woodlands.
With the latest phase at Flimwell, WEL’s David Saunders has achieved his goal of making buildings that demonstrate best practice in sustainable woodland management. The range of buildings and construction techniques at Flimwell make this a true centre of excellence and a destination for architects, designers, students, makers and contractors, indeed anybody with an interest in the potential of native woodlands to support the construction and craft industries. At the same time, architect Steven Johnson’s work is beginning to pose some interesting questions about the potential of an emerging contemporary vernacular architecture.
Duncan Baker-Brown is a director of BBM Sustainable Design and a lecturer at Brighton University’s school of architecture and design.
Architect: The Architecture Ensemble, Steven Johnson; structural engineer: Buro Happold.
Selected suppliers and subcontractors
Units 3-8 Contractor: WG Pritchard & Sons; framing carpentry and erection: The Green Oak Carpentry Company (units 3-4), Inwood Developments, WG Pritchard & Sons (units 5-8); glulam manufacture and shell panel fabrication: Inwood Developments; foundations: Derek Greenwood & Son; joinery: Westgate Joinery; polycarbonate systems: Twinfix; EPDM roof flashings and gutter linings: Firestone; rainwater goods: Lindab.
Units 1-2 Contractor: WG Pritchard & Son groundworks: Derek Greenwood & Son; carpentry: The Green Oak Carpentry Company, WG Pritchard & Son, Inwood Developments; timber fabrication (structure and cladding): Inwood Developments; Accoya joinery: Westgate Joinery; polycarbonate glazing systems: Twinfix; cross-laminated timber panel fabricator (stages 2-3): Binder Holz; internal lining (stage 1): Fermacell insulation (stage 1): Thermafleece by Second Nature Pavatex, supplied by Natural Building Technologies; insulation (stages 2-3): Gutex, supplied by Ecological Building Systems; breather membrane: Tyvek.
Adventure Rope workshop and offices Contractor: Adventure Rope; polycarbonate glazing systems: Twinfix; internal linings: Fermacell; EPDM roofing: Sika Sarnafil.
First published in AT221, September 2011