| BERGEN, Norway/LONDON
BERGEN, Norway/LONDON High-rise wooden buildings, led by "The Tree", a 52.8 meter (173 feet) apartment block in Norway, are claiming a place on city skylines as the timber industry challenges the supremacy of concrete and steel.
New, ultra-strong wood materials are creating a small but fast-growing market for timber used to build big, urban blocks, extending wood's uses beyond the houses typical of Alpine villages or suburban America.
Backers of timber towers say they are greener than concrete and steel, whose production emits large amounts of greenhouse gases. Those industries say felling trees harms the environment if it causes loss of forests.
"Steel was the 1800s materials, concrete 1900s. Now we are in the 2000s and it is time for timber," said Susanne Rudemstan, head of the Swedish Wood Building Council. She said trees must come from properly managed forests to avoid deforestation.
Records are falling fast in the world of "plyscrapers", which get their name from the plywood-like laminates glued together to form the wooden beams used to build them.
The Tree ("Treet" in Norwegian), with a roof terrace atop 14 storeys on the waterfront of the port of Bergen, became the world's tallest wooden apartment block on completion in late 2015, surpassing a building in Melbourne, Australia.
Wood "is definitely part of the solution when we're struggling towards a low-carbon world," said Ole Kleppe, project manager at Bergen property developers BOB.
In September, the world title will go to Vancouver, Canada, when students move into a 53-metre, 18-storey residence at the University of British Columbia (UBC).
That building will save an estimated 2,432 tonnes of carbon dioxide compared to other construction materials, the equivalent of taking 500 cars off the road for a year, UBC says.
"It was quick, it was quiet, and there wasn't a mess," John Metras, managing director for infrastructure development at UBC, said of the construction site.
Elsewhere, construction began last October on an 84-metre wooden tower in Vienna, due for completion next year. And architects are considering even taller blocks, such as a 300-metre "Toothpick" in London.
The cost of building with cross-laminated timber (CLT), one of the main materials, is 10-15 percent more than with masonry or cement in the main European market, a U.N. 2015-16 review said. But prices may fall as the industry matures.
The use of CLT often shortens construction times, the U.N. review says, because many parts can be pre-fabricated. The frame of the Vancouver high-rise took less than 10 weeks to build, which Metras said was much shorter than for a concrete building.
In Bergen, The Tree - using wood from sustainable forests - shows that people are ready to live up high with wood, although residents told Reuters that family and friends fretted unduly about fire risks.
"We think it's very fire-safe," said Soeren Skaar, 24, a psychology student who owns a flat. In a blaze, he said thick wood beams can retain strength better than metal, which can buckle.
Still, some fire detectors have been over-sensitive. "We've had a few false fire alarms ... the first one was a guy brewing beer in the basement," said Rolf Einar Vaagheim, 26, an offshore worker who rents an apartment.
Height records are a showcase for what the timber industry hopes will be wider use of wood in construction, while producers of iron ore and steel struggle with low prices.
Mining companies, such as BHP and Rio Tinto, have teams to assess the impact of new materials and technology.
Even so, the use of innovative wooden materials that allow big spans - such as CLT or glue laminated timber - is still very limited.
"This isn't even making a dent on concrete and steel production - we are addicted to the stuff," said Andrew Waugh, of Waugh Thistleton Architects in London.
His company is building the world's biggest CLT building in London, using 4,000 cubic meters of timber to build 121 homes of up to 10 storeys.
LafargeHolcim, the world's biggest cement maker, says plyscrapers are only a marginal threat to an industry dating back to the Romans, who built the vast concrete roof of the Pantheon almost 2,000 years ago.
"Concrete is the most used building material in the world by far – about 30 billion tonnes (a year) ... It's affordable, resilient in time against weather, earthquakes and fire," said Bernard Mathieu, head of sustainable development at LafargeHolcim.
He disputed that timber is better for the environment than cement production, which he said accounts for 5 percent of world emissions of carbon dioxide, the main greenhouse gas.
By contrast, he said trees also play a role in climate change because they absorb carbon dioxide from the air to grow and release it when they are burnt or rot. Big losses of forests, often burnt to make way for farms, cause up to a fifth of world emissions, scientists say.
The timber industry says, however, that wood from properly managed forests can help to limit greenhouse gas emissions by locking up ever bigger amounts of carbon in buildings.
Finnish wood, paper and packaging giant Stora Enso guarantees its CLT comes from sustainable forests. It says global CLT production capacity grew to around 1 million cubic meters in 2016 from almost nothing a decade ago.
"CLT has the ability to compete with concrete and steel for larger, taller, multi-storey construction applications," said Cathrine Wallenius of Stora Enso.
CLT production began in Germany, Austria and Switzerland and is now spreading beyond Europe to North America, Japan and Australia, said Matthew Fonseca, a forest expert at the U.N. Economic Commission for Europe. He said a recent forecast of 1.3 million cubic meters of global CLT production by 2021 seemed conservative.
Some nations have laws restricting the height of wooden buildings, meaning most demand for wood is for smaller structures.
"We see the immediate opportunity in mid-sized buildings of 2-8 storeys in the United States, where less change is required in building codes," said Justin Adams, Global Managing Director for Lands at The Nature Conservancy, a U.S. environmental charity.
Even wooden buildings have not completely eliminated steel and concrete. The roof terrace of The Tree, for instance, has a concrete floor.
"It was necessary to add weight," said Per Reigstad, of Artec Architects who led the project. The concrete is to keep the building stable in high winds or even rare earthquakes.
(Reporting by Alister Doyle; editing by Giles Elgood)