When leading British architect David Adjaye chose American tulipwood for his London Design Festival project last year (Timber Building Autumn 2008), the key challenge for AHEC was how to treat the timber to withstand several weeks of a damp, cold British autumn on London’s South Bank.
The attraction of the species for Adjaye was its colour variations, from creamy tones through to almost green, which perfectly suited his ideas for reflecting and filtering light in his pavilion design. For a species generally restricted to more utilitarian applications, such as kitchen cabinets, this demanding exterior use opened up the possibility of new markets in sectors such as cladding where the species’ strong performance credentials could be an advantage. But it also created a challenge in terms of treating it to cope with the elements.
BRE testing had already shown tulipwood has tensile strength characteristics comparable to oak, as well as a strength-to-weight ratio equivalent to strength class D40.
Initial trials on tulipwood by treatment producer Osmose were promising. The company demonstrated it could be readily and cost-effectively treated and that it was predictable in its retention of treatment processes, opening the doors to a range of applications.
The 25 tonnes of tulipwood earmarked for Adjaye’s ‘Sclera’ pavilion were primed and treated with Osmose Stabilizing Oil and stood up well to their exposure during the festival. However, after its four weeks in London, the building was auctioned to a private buyer, making formal long-term performance monitoring difficult.
But the project saw the formalising of the AHEC/Osmose partnership into a joint tulipwood development programme aimed at devising processes to add value to the timber and enhance its appeal to a wider market.
Over the last few months Osmose’s research has focused on the key requirements for specifying timber exposed to weathering. This has involved exposing samples, with varying strengths of stabilising treatment, to weathering, while a similar number are treated but not exposed for comparison.
This led to AHEC showing some early treated and exposed tulipwood samples at this year’s Ecobuild. The AHEC and Osmose teams used them as ‘conversation starters’ with visitors around the suitability of this still relatively unknown but prolific American hardwood species for outdoor applications, in particular cladding. And, they say, reactions were positive.
With the initial testing phase completed, Osmose says the exposed samples are looking good. More importantly, the results indicate the treated timber is stabilised, reducing moisture absorption and minimising movement, with the added benefit of protection against mould growth and fungal decay. These encouraging early results will see more extended exposure tests through the summer at Osmose’s Marlow HQ. A more detailed formal research report will then come out in the autumn.
More tulipwood design projects are also under way, including a major outdoor seating installation for this year’s Hay Festival by furniture designer Philip Koomen. According to AHEC European director David Venables, the collaboration with Osmose “looks like presenting some interesting opportunities for tulipwood”.
“Since the Festival, it has attracted the interest of designers and architects around the world. It’s one of the most prolific and sustainable American hardwoods and its strength, versatility and properties make it ideal for exterior use. We know there is a market opportunity, particularly in cladding, and we’re optimistic the research results will give us the opportunity to take advantage of it.”
