Building extensions by Daniel Allen

Engineered wood provides a vertical solution to increasing urbanisation

Today more people live in cities than in rural areas. The global urban population, which now stands at 3.7 billion people, is expected to double by 2050. This trend is more pronounced on continents such as Asia, Africa and Latin America, which demograpic experts predict may collectively account for 96 percent of all urbanisation by 2030.

This urbanisation dynamic is driving ever greater demand for taller structures in increasingly dense cities. Whether architects and construction companies meet this demand using unsustainable materials such as steel and concrete, or by employing innovative, carbon negative mass timber products such as Metsä Wood's Kerto® LVL (laminated veneer lumber), could make a huge difference to the Earth's health and the liveability of the world's urban environments.

Adding floors with mass timber

Vertical value meets density targets

The use of mass timber products in urban construction can help governments and developers meet density targets, while simultaneously reducing environmental footprint and mitigating the effects of climate change. One way of doing this is to add floors made of engineered wood to existing buildings made of concrete and steel.

"Research shows that around a quarter of urban buildings around the world are strong enough to carry additional floors made of wood," says Jussi Björman, manager of Metsä Wood's Technical Customer Service department. "In this way, mass timber offers designers an incredible opportunity to meet the urbanisation challenge."

Urban building sites

Using the tops of existing buildings offers huge potential

Throwing a spotlight on the possibilities of such extra wooden storeys, Metsä Wood's City Above the City contest, which ran in 2016, invited participants to suggest solutions for new housing on top of existing urban buildings.

Architect Nile Greenberg's winning entry in the small-scale intervention category, titled Dear Landlord, proposed a communal wooden structure based on the rooftop of his building in New York City. The design makes use of Kerto-Ripa floor and roof elements, Kerto-S columns and Kerto-Q LVL panels.

"Creating shared ammenities can increase the quality of life in already dense communities, such as those found in New York," says Greenberg. "Adding extra wooden storeys and structures is a progressive solution that I think will become increasingly common."

Berlin-based Sigurd Larsen Design & Architecture's Dachkiez, Village On The Roof design for Berlin was a runner-up in City Above the City's small-scale intervention category.

"Using the tops of existing buildings as a site means that we are occupying a footprint that is already being used," says Sigurd Larsen. "This methodology offers huge potential for densification in Berlin with minimal impact on city sprawl."

Light but strong laminated veneer lumber

Kerto LVL's great strength makes it ideal for adding extra floors

With several projects already completed in Helsinki, the addition of mass timber storeys is increasingly being viewed as an efficient and economically viable way of generating extra urban space. In this regard, Kerto LVL-based products and systems offer multiple advantages.

"Using mass timber, which is relatively light, can help to minimise loading on the building below," says Metsä Wood's Björman. "The high levels of prefabrication and customisation that you get when using Kerto LVL also allow for rapid on-site installation, and additional storeys can easily be 'bolted on' to existing structures."

"Our Kerto-S is the best choice for load-bearing beams and columns," says Metsä Wood's Björman. "Kerto LVL roof and floor elements offer flexible, cost efficient solutions when it comes to space adaptability and long span structures."

Recyclability of mass timber

Mass timber architecture can be easily and efficiently recycled

Today's cities are dynamic, constantly evolving entities. This means that many urban structures have limited lifespans. A recent study found that nearly half of all demolished residential buildings in the United Kingdom are between 11 and 32 years old, while the lifespan of an average Japanese office building is between 23 and 41 years.

The demolition of buildings made from materials such as concrete and steel uses a lot of energy and generates significant waste. Conversely, mass timber architecture can be easily and efficiently recycled, ensuring that the carbon stored in products such as Kerto LVL is sequestered almost indefinitely.

Forward-thinking architects, such as Vancouver-based Michael Green – an enthusiastic participant in Metsä Wood's Plan B campaign and a City Above the City competition judge – accentuate the recyclability of mass timber in their designs. Green's proposed Baobab project in Paris is largely based on prefabricated construction, involving mass timber sheets that can easily be dismantled and used in other buildings.