The american Hardwood Export Council (AHEC) has been sowing seeds for the structural application of engineered US hardwoods for some time, with ever increasing ambition and inventiveness. Today those seeds are clearly taking root in the market, with two significant mainstream construction projects based on the material completing just a month apart.

The first headline-grabbing use of engineered US hardwood as a key structural element was in the white oak glulam and steel supported atrium glass roof of Portcullis House in Westminster ¬– designed by Hopkins Architects and engineered by Arup. AHEC was closely involved with the project, completed in 2000, and went on to put various US species in different engineered formats through structural evaluation and testing.

This led to the Timber Wave, AHEC’s installation at the 2011 London Design Festival (LDF). Designed by architect Amanda Levete and also engineered by Arup, this comprised a spiralling web of finger-jointed, laminated red oak laths.

AHEC’s Endless Stair showcase at the 2013 LDF, designed by dRMM architects, with Arup again as engineer, took things a step on. This explored the structural possibilities of US tulipwood cross-laminated timber (CLT), which formed interlocking, reconfigurable flights of stairs.

The 2016 LDF project, The Smile, marked further evolution. Architect Alison Brooks and Arup delivered a 34m long upward curving rectangular tube structure for the public to explore inside and out, using the first ever industrial scale tulipwood CLT panels, made by German engineered wood specialist Züblin.

The two new buildings in engineered US hardwood draw heavily on these boundarybreaking projects and involved some of the same players.

The first to officially open is the stunning new Warner Stand at Lord’s Cricket Ground. The stand-out feature of the £21m building is the wide, curving fabric and steel-work canopy and the support for this is provided by eleven US white-oak glulam beams, which are up to 23m long, weigh around 4 tons and embody 5 tons of carbon apiece. It’s the first time the material has been used in this format on such a scale and in such a performance critical application, with the beams’ 13m cantilevered section extending out above 2,656 spectators.

Part of the reason white oak glulam was selected was its environmental credentials, said Philip Johnson, director of architects Populous.

“We and the client, the MCC, wanted the stand to be and be seen to be as sustainable as possible, and what could be more sustainable than timber from well-managed forests,” he said.

But according to Giancarlo Torpiano of project engineers Arup, the main criteria for the choice were also engineering-driven; the combination of white oak’s furniture-grade finish and structural performance.

“It’s relatively dense so has very good strength and stiffness properties enabling us to reduce the size of the beams, which was important architecturally.” he said. “Since the timber elements run from an external, uncontrolled environment, with relatively high fluctuations in temperature to an internal, controlled one, the thermal properties of timber (as opposed to steel, for example) were also a major advantage.”

The beams were manufactured by Hess Timber in Germany and exhaustively trialled by the Stuttgart University Materials Testing Institute, or ‘the godfathers of glulam’, as Hess head of sales Markus Golinski called them.

The development process wasn’t all plain sailing however. While the density of the timber was key to its selection, it posed challenges too.

“Our usual glues wouldn’t absorb sufficiently so initially we had some delamination,” said Mr Golinski. “But we ultimately found a modern melamine product that performed. So success was down to latest adhesive development. Ten years ago these beams wouldn’t have been possible.”

The other engineered US hardwood construction project, the new Maggie’s Cancer Care Centre in Oldham, was also not without its obstacles, notably in architect dRMM persuading the client of the benefits over standard CLT of the material in tulipwood, more generally regarded as a paint-grade species for mouldings and cabinet carcassing.

“We explained that the variegated tulipwood and quality of finish would make the structure feel like a fine piece of furniture, and that we were using a species that could be expressed extensively to maximise the proven psychological and therapeutic benefits of timber construction,” said project architect Jasmin Sohi.

“We partly chose tulipwood because of our experience with its performance in Endless Stair; also because it’s among the most prolific of US hardwoods. We wanted to transform its status and show it as a beautiful alternative to default hardwoods and softwoods,” added dRMM founder partner Alex de Rijke.

The rectangular, flat-roofed building sits on 4m steel legs. The CLT panels, made by Züblin in the same production run as those for The Smile, form one straight outer wall, which acts as a full-height beam. The other, combined with a curved inner CLT wall, performs as beam and bracing, containing rooms and services between. In the centre is a curved glass-walled light-well, and at either end of the building, full-width glazing with views to the Pennines.

Tulipwood also features in the ceiling, formed by slats made from panel offcuts, and in the exterior cladding, comprising thermo-treated timber in a bespoke corrugated profile.

AHEC was closely involved in terms of providing technical advice and in materials sourcing for both projects, supporting liaison between architect, engineer and timber suppliers. Robinson Lumber provided the white oak for the Warner Stand, while for Maggie’s, tulipwood for the CLT and thermo-treated cladding was supplied by Middle Tennessee Lumber Co and Northland Forest Products respectively. It was an approach all three suppliers appreciated, as summed up by Robinson’s Hank Marchal.

“Putting together these project driven initiatives with the raw material highlights the potential of what is really an underutilised natural resource,” he said.

AHEC European director David Venables said both buildings could be potential game-changers for US hardwood.

“They represent the real commercial world of construction – architects, engineers, builders and their clients – responding to something we’ve put on the table through our various projects and concluding that it’s workable,” he said. “Our aim throughout has been the long-term commercial success of our industry. It’s been a sometimes complicated journey, but these buildings show we’re getting there.’