The success of last year’s Better Timber Buildings conference even took its organiser by surprise, according to TRADA chairman Nick Milestone, as he introduced this year’s event to around 150 construction professional delegates.
Last year’s TRADA conference “created even more attention than we thought it would”, said Mr Milestone. And that may have been surpassed this year, he concluded at the end of the event on November 27.
As last year, the conference was designed to “educate, inspire and empower architects, engineers, suppliers and clients to design and build better timber buildings. This year the conference had a strong emphasis on engineered wood products, particularly cross-laminated timber (CLT) and laminated veneer lumber (LVL) and speakers represented a broad cross-section of the construction industry, from client to manufacturer.
Sam Elliott, development director at The Office Group (TOG) kicked off proceedings with a client’s perspective of specifying and building with timber. TOG has developed more than 50 buildings to date and, focusing his presentation on The Black and White building in Hackney, in London, Mr Elliott explained that every project was bespoke and underpinned by design principles of biophilia, sustainability, wellness, feature joinery and exposed structural timber.
The structure comprises a concrete basement box and, above ground, a BauBuche beech LVL frame supporting CLT slabs.
The Black and White building’s former life as a veneer drying factory provided the inspiration to use timber, although TOG was already “totally sold on it as a structure and a finish” and had previous experience of glulam and CLT projects.
Mr Elliott highlighted some of the obstacles to customers using timber and suggested solutions. These included the fact that the use of structural timber is “counter cultural” in the UK, eliciting a “fear of the new”. The solution was to pick consultants who had worked with it before, he said.
The cost premium was offset by savings made in time and on raft foundations and fit out wall linings, he added, and the risk of damage during installation could be controlled by tight onsite management. Fire risk could be tackled by using an experienced consultancy team and an “active, questioning fire design process”, while acoustic concerns could be addressed by installing acoustic grade raised access floors to prevent reverberation.
The outcome, said Mr Elliott, would be “a beautiful, sustainable, design-led building that people will want to work from”, adding that TOG has faith that it will achieve a higher price for buildings made with timber.
Where the timber industry needs to raise its game, he suggested, was in education and advisory support regarding compliance and regulations; proactive material testing, so the client didn’t have to do it themselves; more precedent schemes, providing proof of concept and proof of the value of timber buildings to agents and the market; regulatory and financial recognition of the investment in sustainability – ie wider recognition of embodied carbon benefits, BREEAM and so on; and recognition of the wider benefits of offsite construction, including a reduction in deliveries, less dust and noise and safety factors during construction.
Mr Elliott also drew attention to the challenge of sourcing raw materials, with much of the glulam and LVL coming from Europe and often from single suppliers.
Glulam and BauBuche beech LVL are also central to the design and construction of the latest Maggie’s Centre. The drop-in facility for cancer patients – the 25th Maggie’s Centre – is being constructed at St James Hospital in Leeds and is designed by Heatherwick Studios. It is due to open in the spring.
Nick Ling, technical design lead at Heatherwick outlined the challenges of building on the tiny, very steeply sloping site, which, despite being surrounded by the ambulance route into A&E will provide a haven for the 110 visitors that are expected each day.
The building comprises a series of “planters” built on three platforms stepping down from the slope, which drops 6m. As the ground is full of rubble from the building of the adjacent car park, the Centre had to have “the lightest touch”.
As it’s built on the only green space left on the hospital site, the Centre will be surrounded by garden and feature a lush green roof, supported by propped cantilever spruce glulam fins.
Along with glulam, the building also features CLT and BauBuche LVL machined by Blumer Lehmann in Switzerland.
“The factory can cut any shape so we can start to be really playful,” said Mr Ling, adding that BauBuche was being used for stairs, window cills and joinery items.
He added that in order to optimise the structure, Heatherwick felt it really needed to understand fabrication and the team had been impressed by Blumer Lehmann, not just for its technical prowess but also for its sustainability credentials.
In the subsequent Q&A session Mr Ling said that Heatherwick had found timber to be “a very forgiving medium” on site – although it did build tolerances in – and that the decision to use timber for the project was an answer to “the call for all of us to be brave and to have specialists around the table asking why we can’t do this and advising clients what is in their best interests”.
CLT was also under the spotlight of Jennifer Eriksson, a timber engineer with Stora Enso’s Building Solutions team. Ms Eriksson said that Stora Enso had spent €150m on R&D last year and went on to explain the team’s work on the moisture dynamic of CLT, research on which it is collaborating with TRADA.
CLT doesn’t necessarily follow the same rules as other timber products when it comes to moisture, with ingress and subsequent drying influenced by thickness, the number of lamellas and so on. Ms Eriksson stressed that it was essential to have a management plan in place on any site to reduce the risk of moisture ingress in the first place.
The project’s aim is to investigate the moisture dynamic of CLT; find the most time and cost effective drying regime; and minimise stresses on timber, adhesives and joints. Its conclusions will be best practice guidance, which will increase confidence in the industry.
The research is in two phases, during the first of which CLT panels are wetted with water containing a trace dye every two days and every two weeks.
A total of 1,500 moisture sensors are located in all five depths – one row in the middle of the panel and one nearer the joint. After eight weeks the panels are cut into pieces and examined.
New panels then have to be wetted for eight weeks and are then dried in a variety of ways – with a roof membrane on top of the panel; uncovered with ambient/heated airflow; and uncovered with no drying.
The project features a “bonus test” to check how well RFID tags work within CLT panels.
“Tags were placed in the first and second glue line in the lamellas and were tested to see if they worked after going through manufacturing and the press – and they did,” said Ms Eriksson. “More work needs to be done but if they match what the moisture sensors record, it will allow the moisture content to be checked without removing the cladding – a lot of doors will open.”
Steve Cook, Wilmott Dixon’s product improvement and innovation manager gave an appraisal of the major forms of off-site timber construction and some tips on how to play to each one’s advantages.
Glulam wins on aesthetics, for example and is ideal for corrosive environments such as swimming pools, while CLT is very thermally efficient and well suited to low energy buildings. “It is our material of choice for Passivhaus buildings,” he said.
Timber was also very flexible for modular construction, he added, while platform timber frame, which makes up about 30% of new house construction, is looking to integrate further elements, such as pre-installed windows.
Mr Cook said that there is “increased noise and discussion about offsite” prompted by the Farmer Review and the government’s recent acceptance of it but added that there are many “soft factors” than can affect choices.
For example, speed of construction is not always an advantage as if a development is built before the units can be sold, it impacts cash flow. Other factors such as whether local spend and local labour are important should also be considered, as should running costs. “The people who construct the buildings aren’t necessarily the ones who will own them,” said Mr Cook.
Perhaps with his Grown in Britain chairman’s hat on, Mr Cook also highlighted the need to change the UK public’s perception that cutting trees down is bad. “Fifty-six per cent of UK woodlands aren’t managed and [the public] have a completely different attitude to Scandinavia where it’s seen as a crop. We really need to change people’s understanding of trees [to promote the use of timber in buildings].”
Following presentations that showcased exemplar timber buildings, Dr Keerthi Ranasinghe, senior lecturer and programme director for civil engineering and quantity surveying at the University of Wales, pointed out that none of them would have been built without Eurocode 5.
Dr Ranasinghe, who sits on TRADA’s advisory committee and on the IStructE research panel, has just authored the organisations’ joint second edition of the Eurocode 5 Manual.
The second edition, which was three years in the making, reflects the many changes to supplementary documents since the 2007 first edition, including the publication and withdrawal of several standards and national annexes.
It includes code changes to sections on material properties, bearing capacities, connections, glulam, racking, and fire, along with the insertion of new sections referencing CLT and the new product standard. In addition, further amendments have been made which take into account the feedback of readers and consulted practising engineers. (For more, see www.ttjonline.com/news/tradaupdates- eurocode-5-guide-7537016/)
Danny Hopkin, technical director of fire risk specialists OFR Consultants turned the focus back to mass timber. In just the same way that moisture ingress into CLT isn’t yet fully understood, its fire resistance credentials are also under investigation.
Claims about the performance of CLT in fire, such as “it’s not like kindling” and “it has inherent fire resistance” weren’t necessarily untrue, said Dr Hopkin, but they were “trivialised”. “The issue is more complex and there needs to be more context,” he said.
The main issue seems to be that the standard fire test hasn’t really changed in 100 years and is not compatible because the furnaces weren’t designed for mass timber, skewing test results as a consequence. Dr Hopkin’s paper in TRADA’s ‘Timber 2019 Industry Yearbook’ explains further.
Alex Abbey, a partner at Cullinan Studio, gave his thoughts on what clients want and need to know when procuring timber buildings and suggested that they should be considering timber in the context of the climate emergency. “Engineered wood is a potential way out of this,” he said.
Mr Abbey said that the design of buildings had been a social pact and that could now be extended to an environmental pact. Referencing TRADA’s “Procuring engineered timber buildings” book, he said the guide was a good one-stop-shop and would answer many clients’ questions, including on where timber is sourced and descriptions of the different products available.
The guide also summarises the cost of projects, comparing CLT with concrete, demonstrates the value of timber – its light weight and durability characteristics, for example – programme speed and particular properties, such as being bendable.
“There is a growing wealth of knowledge in the industry in how buildings can be designed but lack of knowledge among some contractors means some designs can be watered down,” he cautioned. He added that timber’s sustainability, wellness and durability credentials should all be shared with clients.
Experiences of building with mass timber in North America and, closer to home, in Wales, were shared by Robin Lancashire, senior timber frame consultant at BM TRADA.
Mr Lancashire and TRADA’s university engagement manager, Tabitha Binding, had joined an Erasmus+ Knowledge Alliance trip to Canada to see the progress of mid-rise and tall timber buildings in the country.
“Canada’s journey in mid-rise [timber] construction is fairly new,” said Mr Lancashire. “It started after a change to building codes in 2015. The 2015 edition of the National Building Code of Canada permits the construction of six-storey residential, business and personal services buildings using traditional combustible construction materials.”
Since then British Columbia (BC) has led the way with 417 mid-rises (four storeys or over) constructed or under construction, followed by 149 in Ontario, 44 in Quebec, 30 in Alberta and four in Saskatchewan.
The variation in the figures is explained in part by the significant increase in the volume of available timber in BC due to the mountain pine beetle – “they are getting on and using it,” said Mr Lancashire. Meanwhile, he added, in Ontario there were higher insurance costs, regulations regarding non-combustible stairways, a proactive concrete industry and workmanship quality issues.
Likewise, Quebec had skills challenges, low concrete prices and “little market acceptance for wood in projects over four storeys”.
Over the border in the US, where Mr Lancashire had spoken at the International Mass Timber conference in Portland, Oregon in March last year, progress is still somewhat behind Europe.
“Despite having lots of forest cover and timber in the US they are still importing [engineered timber] as they don’t have the machinery and technology,” he said. “But they are getting tooled up.”
Mr Lancashire concluded his presentation with a look at the Home Grown Homes project led by Powys County Council, funded through the Rural Development Programme and delivered by Woodknowledge Wales, with delivery partners including BM TRADA and Coed Cymru.
The project aims to improve the quality of Welsh homes through building performance evaluation and whole life carbon analysis; improve the quality of offsite manufacturing through collaboration, greater systemisation and application of low carbon standards; and to improve the business case for expanding Welsh forestry through stimulating construction timber demand and supply.
In the final presentation, Ed Suttie, research director at BRE spoke on the subject of the role that timber can play in healthy buildings, a subject he covered at TTJ’s Wood and Wellness conference in February 2019.
The next Better Timber Buildings conference will be held on November 11.
