The Ethical Case for CLT

Earlier this summer we were honored to present at the 2016 Passive House Conference in New York City. Our Certified Passive House Designer Stas Zakrzewski teamed up with Matthew Lee of Lee Properties Group and talked about challenges and opportunities offered by CLT, or cross-laminate timber construction.

We’ve distilled some of our points and in this article we’d like to share with you the ethical case for working with CLT, as well as demonstrate why wood is increasingly being called the building material of the 21st century.

As designers who are passionate about Passive House design, we’re all too conscious that the environmental challenges facing us are immense. We are well aware of our obligation to combat rising greenhouse gas emissions and carbon dioxide production in the face of a rapidly urbanizing world.

So as architects what can we do to change this? As you may know, at ZH we have been making it our business to implement Passive House design wherever we can, no matter what the scale of the project. Every day we strive to de-carbonize our building stock by creating super energy efficient buildings with very low operational energy.

However if we want our buildings to be truly low-carbon and energy efficient, there is another thing we must consider – the energy required to build the structure in the first place – the embodied energy. As a performance standard Passive House doesn’t account for this, and there has even been suggestion from some quarters that because of the extra materials that go into building a Passive House building, they can require more energy to erect than traditional construction. Although the operational energy is still a much larger share of a building’s Life Cycle Energy consumption, as we reduce our operational energy through Passive House design, embodied energy becomes a greater and greater proportion of the total energy used.

CONSTRUCTION TYPOLOGY

So now think about the modern city – vast jungles of steel and concrete. While both of these materials have great qualities of their own, their production requires heavy industrial processes and high temperatures, which demands huge amounts of energy and produces tonnes of carbon.

LOW ENERGY BUILDING

Wood has always been considered a more environmentally friendly alternative, however traditional stick frame buildings aren’t easily scalable beyond a few stories. Throw in the historical precedent of fire in densely packed stick frame cities and you can see why we have had to resort to steel and concrete to build in the urban context.

Or at least that WAS the case.

Mass engineered wood products like cross laminated timber (CLT) and glulam have been popular in Europe for a long time, but it has only been in the last decade or two that they have been really hitting their stride. Unlike concrete and steel, engineered wood products like CLT require very little energy to produce and don’t rely on the extraction of large amounts of finite materials from the ground. Strong and robust, these timber products are being heralded as the solution to building big with wood. There are already towers up to 10 stories tall, and there is even a proposal for an 80-story tower CLT tower in London – which has already gained the moniker ‘the Splinter’.

CARBON SEQUESTRATION

The environmental impact of wood is reduced even further once you consider carbon sequestration – the process by which carbon is removed from the atmosphere and stored in a solid or liquid form.

Younger trees tend to sequester more carbon, while dying trees release carbon as they decay. By using only young trees, turning them into wood products, and then replanting others, a continuous cycle can be created by which carbon is sucked from our atmosphere and used to build our buildings

ACCOUNTABILITY + STEWARDSHIP

You might be wondering, can CLT have really benefit the environment if it is encouraging large scale harvesting of trees? For mass timber to really make a difference it’s vital that architects and specifiers only work with manufacturers which engage in responsible, certified forestry practices. Fortunately, there are plenty of suppliers like this out there – in part because the nature of the industry lends itself to accountability. From the time the tree is harvested, until the finished panel arrives on site, the wood is under the stewardship of a single company bound by stringent requirements of certification agencies such as the Forest Stewardship Council. Thanks to regulations and organizations like this, net forest growth has been increasing at a faster pace than forest removal in North America despite a rapidly growing population.

We recently visited the Nordic Factory in Quebec, Canada, which is one of the leading producers of CLT in North America. During our tour of the Nordic Factory we learned first-hand about the production process of CLT. We left that factory solidifying our belief that CLT is one of the most sustainable and low carbon building materials on the market. We also believe wholeheartedly that mass timber is the ethical solution for building sustainably to accommodate the world’s continued population increase – especially in urban areas.

The metropolis of tomorrow could be a forest of timber buildings. CLT construction is much more feasible than many think. Yes it is a new technology, but in combination with Passive House strategies it promises an incredibly exciting and extremely ethical choice for architects who are committed to making a positive impact on their built environment.