Summary
• I-joists are continuing to take market share from solid timber joists.
• National housebuilders have started to open up more sites.
• There has been an increase in interest in I-joists for roofs and walls.
• I-joists are being incorporated into designs for the London Olympic venues.
• The increased use of MVHR systems is favouring the open metal web joist.

“Interesting” is the word that Brian Robertson, general manager of James Jones & Sons Timber Systems Division, uses to describe the current state of the UK I-joist market. Although I-joist suppliers are only too aware that market conditions remain challenging, there are enough signs of life in the housebuilding market to engender “cautious optimism”.

For James Jones, this optimism has seen the company reinstate a night shift at its manufacturing base in Forres, courtesy of a healthy order book, and the underlying trends look positive (see pxx). “There’s definitely been a degree of improvement in the market – and it seems to be holding up longer than we anticipated,” said Mr Robertson. “However, we’re conscious that the market traditionally dips in the run-up to Christmas and the dark months of January and February are always slow times for construction, so we’re anticipating a falling off in the market in the short term.”

Despite the caveat, his sentiments are shared by the market’s other leading suppliers. Shortages and price increases levied on solid timber over the past few months have seen a gradual switch to I-joists, particularly given that less material is needed in their manufacture. This has also opened up the market to smaller builders and roofing contractors. “Once tried,” said Masonite Beams UK sales manager Neil Lewis, “such users are converted for the longer term.”

Good news

It’s certainly good news for I-joists. “Many of our customers have seen improvements in activities over the last few months as they continue to serve their loyal customers and target wider markets both in terms of consumer style and geography,” said Simon Jones, business development director at Boise Cascade.

National housebuilders have indeed begun to open up more sites after mothballing many developments. Meanwhile, the self-build market – a big user of engineered I-joists – has woken up and many timber frame companies are experiencing a steep rise in enquiries from this sector. The public and commercial sector has continued to build during the downturn, albeit at a slower rate.

And, although Brian Robertson believes that I-joists have probably reached capacity in domestic flooring, he’s seen an increase in the sales of JJI-joists for walls and, particularly, roofs. This, he said, is being driven by the growing interest in the Code for Sustainable Homes.

“Everyone is conscious that Code level 6 will be with us very soon and all the big builders are working towards 2016. We’re talking to a range of major developers using both timber frame and masonry, who have projects in both the public and private sectors.”

Advantages over solid timber

I-joist suppliers say their product offers a number of advantages over its solid rival. These include: stability, both in terms of strength and price; availability in terms of complete pre-cut component packages to site within a matter of days; simplicity and speed of construction; and fewer post-completion performance issues.

And, said Kevin Riley, building solutions director at Finnforest UK, it’s not just about the product. “The technical service, design software and advancement of new build techniques facilitated by the I-joist – this is what is delivering benefits to builders, timber framers and distributors alike,” he said.

To prove his point, Mr Riley said the additional strength-to-weight ratio of the Finnjoist means that enhanced performance of the floor zone can be achieved in both residential and non-residential developments such as schools, commercial buildings and, more recently, in nursing and care homes.

Neil Lewis, too, has seen developments in the schools, nurse accommodation and nursing home sectors, area where the government is pushing the green issues along with energy-efficiency requirements. “I-joists remain stable whether it’s a 160mm or 400mm section,” he said.

“Using I-joists in wall and roof applications in the wider sections offers the ability to receive thicker insulations, thus providing extremely energy-efficient buildings with lower U-values. Deep sections allow wider roof spans and can easily accommodate services.”

The proof is already out there. I-joists and LVL. James Jones’s JJI-joists have been used in roofs, walls and floors in the new Scottish Natural Heritage joint offices in Golspie in Sutherland and the company is currently supplying I-joists for roofs, ceilings and floors for a new bird observatory on Fair Isle.

Roof and wall applications

However, it is the growth in roofs and walls that could be the biggest opportunity for I-joists going forward. Simon Jones said Boise Cascade’s products are being used in a variety of demanding applications. “These can be roofs, from the relatively mundane house attics to vast waveform industrial/commercial type projects,” he said. “We also see architects and engineers using I-joists in thick wall applications to maximise the thermal properties of the building envelope.”

Manufacturers aren’t resting on their laurels when it comes to developing their products. Mr Jones said Boise Cascade’s new 32mm-thick Versa-Strand rim board is finding new fans in the timber frame industry. “We are working with our customers to develop wider product applications in floors, ground floors, roofs and walls,” he told TTJ.

Meanwhile, with the European Technical Approval for the BCI-joists due to be announced within the next few weeks, Boise Cascade has launched its EC5 version of BC Calc and BC Framer to customers and is conducting a series of introductory seminars throughout the country in November.

At James Jones, improvements in material sourcing have yielded timber which is comparable to C30 grade, which the company says gives major advances in JJI-joist strength and stiffness: up to 35% improvement in stiffness, and span gains of up to 254mm at 600mm centres and 355mm at 300mm centres.

With offsite construction techniques increasingly being favoured for the greater control they offer in achieving crucial technical details – vital to a building’s overall performance – the future for I-joists looks assured.