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Faster, cheaper | Putting the case for timber structures

metsa wood

Timber structures are fast growing in popularity for their speed of construction and the architectural possibilities they open up.

Productivity of manufacturing companies has risen steadily from 1990s whereas the productivity of construction companies has stayed flat or even declined. Faster building projects lead to faster revenue, thus saving money and time are the main drivers for increased usage of prefabricated elements.

And one company urging the increased use of prefabrication is Finnish timber provider Metsa Wood.

Okay, it’s got a clear vested interest in singing the laurels of timber. Forestry in Finland is big; the €900M-turnover Metsa Wood is part of the €5bn-turnover Metsa Group, owned by 116,000 Finnish forest owners and employer of 9,600 people. The broader timber industry employs another 300,000 people. It’s a big export and as such is a big part of the Finnish economy.

So yes, Metsa has a vested interest. And in particular, making the case for it to be used in place of other materials. But the argument has merit.

“The construction industry hasn’t been able to increase its productivity rate in 25 years,” says Metsa Wood executive vice president Esa Kaikkonen. “This is not a Finnish thing, it’s a global thing. I don’t know why, but it’s with us.”

Kaikkonen cites a report from McKinsey&Company last year that found the productivity gap between the manufacturing industry and the construction sector is currently 1.7-fold.

He also cites an earlier report – in 2011 – from McGraw Hill Construction that found that 70% of projects that used prefabricated elements were delivered faster and 65% were delivered for lower cost. He also draws on evidence from Sweden that almost 80% of projects where prefabricated products were in use produced less waste.

“Our elements should be easy to use - easy to design and easy to work with – to increase that productivity,” he stresses.

Kaikkonen’s view is that there should be more focus on the speed of the process without compromising quality. Shorter building time and easier design leads to faster revenue, but is also an opportunity to meet the rapidly growing needs of urban construction and sustainability demands at the same time.

“And construction must become more sustainable,” he asserts. “Urbanisation will continue. We’re basing our business plans on this,” he says.

Worldwide, there is a movement towards greener buildings and indeed towards timber buildings.

“It is only a matter of time until the first timber skyscraper is built.”

“There is a big trend globally towards green building policies,” says Kaikkonen. “The US is updating its codes to allow taller timber buildings. China is particularly interesting and is updating its codes to allow for [taller] timber buildings… And China usually does what it says it will.

Australia changed its building codes to allow timber framed structures up to eight storeys in height in May this year.

As the result of a two-year research project, the country’s National Construction Code has been altered so that the permitted height of wooden buildings increases from three storeys to eight.

The new regulations are more line with buildings codes in North America and Europe, where many seven- to nine-storey wooden buildings have been completed, and a series of timber-framed skyscrapers are proposed.

Finland adopted a similar change to its building codes in 2010, paving the way for an eight-storey wooden apartment block – the tallest of its kind in the country – to be completed last year.

And back in the UK in April, engineers and architects presented plans for an 80-storey timber-framed skyscraper. The 300m high Oakwood Tower would sit within London’s Barbican. It’s been worked on by a team which includes civil and structural engineer Smith and Wallwork, alongside researchers from Cambridge University’s Department of Architecture and PLP Architecture.

The team is looking at the use of timber in tall buildings from the viewpoint of its benefit as a renewable material, potential reduced cost and quicker construction, safety aspects and building weight.

As Smith and Wallwork co-founder Simon Smith said in unveiling the plans: “Timber is our only renewable construction material and in its modern engineered form it can work alongside steel and concrete to extend and regenerate our cities.

“It is only a matter of time until the first timber skyscraper is built.”

So Metsa is hitting what it sees as an open and inviting market. And its high-strength Kerto LVL (laminated veneer timber) prefabricated roof and floor elements are at the heart of its push.

LVL is produced from 3mm thick, rotary-peeled softwood veneers that are glued together using weather resistant adhesive. Its high strength derives from homogenous bonded structure and the end result is strong and dimensionally stable – it does not warp or twist.

“LVL is almost a commodity product in the US and Canada but not so well known in Europe,” says Kaikkonen, who wants to spread the word. “We are not entering the building industry so we need the building industry to use our products for themselves,” he adds.

Kaikkonen says the results are there to see. “It’s fast. Our modular structures have a claimed 20% reduction in construction time,” he states.

He cites Finnish supermarket giant Tokmanni that is using its Kerto LVL to build its new stores and claiming construction rates 30% faster as a result.

metsa wood prefabrication karisma shopping center kerto roof panels interior

Karisma shopping centre features a Kerto roof panel interior

Metsa Wood R&D engineer Jussi Bjorman says all shapes and sizes of LVL are made to order at the company’s mills – adding to the efficiency story. “It’s a customised product so there is minimum waste – either in transport costs or on the construction site,” he says.

It’s easy to design with and easier still to assemble, he adds. Assembly is done using standard tools – “it is still timber”, he notes – and Metsa’s Finnwood software is available for design to Eurocodes with all national annexes available.

So how does LVL compare to glued laminated timber (glulam) that is rather more prevalent?

“LVL can be used as beams, panels, rafters or columns,” explains Bjorman. “It give you the freedom to create unique solutions.”

He cites the eye-catching sports centre in Clamart, France which opened in April this year and features variable curvature LVL beams in its 40m long roof structure (see below).

metsa wood clamart long span wood frame kerto lvl 2

Metsa Wood’s Clamart long span wood frame using Kerto LVL

“Take Clamart. Usually you would use Glulam but there were some tight radiuses that work better with LVL,” he explains.

So what’s the catch?

“LVL is significantly more expensive,” admits Bjormann. “It could be twice as much.”

But comparing it on a pound for pound basis is too simplistic says Metsa Wood senior vice president business development Mikko Saavalainen.

“Comparing m3 to m3 is not the way to understand it. We believe the evidence is there [that using timber is more efficient].

And Metsa isn’t saying that everything should be built out of LVL, or even timber generally.

“The idea is not to build everything out of wood, but to use wood in the best place,” concludes Saavalainen. “What we’re trying to do is open up the construction process in how to use wood to make the process lighter, faster and more sustainable.”

Clamart shows the way for LVL

The innovative use of prefabricated timber products has enabled an ambitious architectural vision to be fulfilled in the French town of Clamart.

 

metsa wood clamart long span wood frame kerto lvl 3

Metsa Wood’s Clamart long-span wood frame using Kerto


Its new sports centre has a complex shape designed to follow the curves of the landscape. The design was based on the definition of the architectural concept by Gaétan Morales and his team from Gaëtan Le Penhuel architects and the technical solution linked the façade and roof together in a continuous structure. The sports complex includes a gym, a martial arts dōjō, a track and field area, and a tennis court – all in one floor.

“This project is really exceptional, not just because of its size but also because of its shape. With its curves, unusual dimensions and wide opening in the roof for the track and field area, very few pieces of timber used were identical,” explains Antoine Roux, structural engineer at engineering contractor Charpente Concept.

Due to its complex geometry, the roof and framework design of the Clamart Sports Centre posed advanced technical and aesthetic challenges, such as the double curvature in certain areas of the roof. Metsa Wood’s Kerto LVL replaced glulam, which is generally used for building long curved beams.

The use of Kerto LVL enabled the widest possible freedom of curvature to support the architectural vision of the complex. Metsa Wood’s delivery consisted of Kerto LVL rafters for the building’s frame and roof structure, covering an area of 5200m2. The largest rafters used were 1,200mm deep with a maximum beam span of 30.4m between supports.

With the complex geometry of the wooden roof structure, the main challenge was to ensure that the elements supported the loads imposed by the shape of the roof. The stability of the building was achieved by a grillage frame structure made of Kerto LVL beams. In total 562 secondary rafters were used with lengths varying from 2.8m to 4.3m, connecting with 41 cross-members with a total length of 40m. The roof structure was all supported on 28 longitudinal columns with lengths between 5m and 8.5m.

The high connection strength of cross-bonded Kerto was found to reduce the amount of required connectors and thus the size of the steel plates. All of this allowed significant savings for the contractor, both in terms of material and time. The mechanical properties of Kerto LVL, notably the cross veneers, also improved the resistance of fasteners. The hollow cavity of the beams was used to hide most of the steel plates and embedded metal fasteners such as brackets, bolts and dowels.

And when it comes to sustainability, timber can claim some good stats around energy consumption.

Let’s face it, the construction sector uses a significant share of global energy – and a large part of this goes to the production of building materials. Metsa’s wood mill in Lohja produces Kerto LVL in a way that actually generates more bioenergy than is used in the process. The rest of the bioenergy is used by the surrounding town.

The mill is a great example of the joint production of construction products and bioenergy. First, as much of the wood as possible is used for Kerto LVL. Part of the sawdust and wood chips generated in processing the engineered wood are used for pulp, and the rest for bioenergy production. A bio heating plant has been built next to the mill in order to capture the full potential of the production.

The heat energy produced at the plant covers the needs of the mill – and the excess is sold for district heating to the surrounding town, which makes the Lohja Kerto LVL mill 100% energy self-sufficient. The heat produced for district heating compensates for the purchase of electricity needed for the mill’s operation.

The remaining heat from the Kerto LVL production process is sold for district heating to the town of Lohja. “The local bio heating plant is a significant support for reaching our ambitious low carbon energy goals,” says the mayor of Lohja, Mika Sivula. Lohja is part of Finland’s national scheme to reduce greenhouse gas emissions by 80% by 2030. “Due to the bio heating plant, we have reached our first milestone: 15% reduction of greenhouse gas emissions by 2016”, says Sivula. The plant covers 80% of Lohja’s heating.

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