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Construction: Is Timber The Future Of Zero Carbon Buildings?

Covid has highlighted the need to rethink cities as self-sufficient greener ecosystems.

Xiong’an, the highly sustainable city blueprint located 80 miles from Beijing in Hubei will have housing towers made of 100% cross lateral timber. A testing ground for future urban innovation, the “self-sufficient city” is expected to be completed by 2035 and will be the trademark for a new pattern of urban development in China.

Why cross lateral timber (CLT)? Simply because it is one of the (if not the) most sustainable construction materials you can build with. CLT is produced by pressure-gluing three, five, seven or 11 layers of timber such that the wood grain of each layer is at 90 degrees to that of the next layer’s, distributing weight in both directions. It is used for load-bearing walls, floors or roofs. Another complementary material, glue laminated timber (Glulam) is made less dense and is therefore lighter and more flexible. It is the material of choice for arched shapes or curves in beams or pillars. While CLT and Glulam have been used for some years, their reputation as “negative carbon materials” have put them centre stage of a low-carbon future. 

Cement is the most widely used substance on the planet. It laid the foundation of our modern lives. Its longevity, safety, acoustic performance and thermal inertia make it the material of choice for construction. Combined with steel, it is a very solid and durable material, but it has a negative environmental footprint. It is responsible for 8% of the world’s Co2 emissions^*. In fact, half of its emissions are released from a chemical reaction during its production process (clinker). Besides this, its manufacturing process is energy and water intensive and involves extensive sand mining. As a material, concrete dust fuels air pollution and when no longer in use, concrete goes straight to landfills.

Timber’s advantages are numerous. When harvested from sustainably managed forests, it has “negative” carbon footprint. What makes wood interesting is that it is a net sink of Co2 emissions as the carbon absorbed from the atmosphere by the trees is locked into the structure. In terms of proprieties, “CLT has a slower burning rate compared to cement, is self-extinguishing, does not release toxic fumes and is light” says Marc Delfeld, co-founder of Wood Solution, an engineered wood construction system. CLT also speeds up construction – wood can be precision-manufactured, is delivered onsite and can be mounted straight away requiring less manpower than cement and produces less waste (which is produced on site)– This makes it A very cost-efficient alternative to cement. Thanks to CLT and Glulam, high buildings can be made entirely of timber. Norway’s 19 stories Mjøstårnet which was completed in 2019 is the tallest timber building in the world at 85 meters.

Although CLT and Glulam have a foreseeable future in a low carbon economy, their use is not yet widespread. Some companies like Dragages (Bouygues) have set ambitions to reduce their carbon footprint and this involves the use of timber. The company aims for 30% of its 500 yearly constructions to be built in timber or with mixed materials which include timber by 2030. “This targeted reduction of projects carbon footprint will have to go together with an increase use of wood as wood stores carbon during its growth and continue to do so even after it is installed as a building structure. On the contrary concrete and steel are emitting carbon, so wood is one of the best construction materials when it comes to carbon footprint.” says Antoine Gondard, Regional business development manager at Dragages.

In Singapore, timber is not yet a visible component of green buildings. For Antoine Gondard at Dragages, the lack of supply of certified timber in Asia is a major hurdle: “To date, it has been difficult to find suppliers in Asia that propose certified timber under the Eurocode^** [E.U. standards which were also adopted by Singapore]. The timber used in projects in Singapore is still mostly sourced from Europe (Austria, Germany, France...) which unfortunately negatively impacts the overall carbon footprint of a project.”

Timber’s sustainability has not been tested on a massive scale and ensuring that the forests the wood come from are all sustainably managed (or FSC^*** certified) is a challenge. The construction sector is working on new low-carbon cement and recycled cement technologies, but the renewability and carbon sequestration features of wood will be hard to match.

Will CLT be a game changer? Perhaps not but it will certainly play an important role in making cities feel greener and more “circular”.

_{^*2015. Trends in global CO2 emissions: 2016 Report ©PBL Netherlands Environmental Assessment Agency The Hague, 2016
^**Eurocode: 10 European standards specifying how structural design should be conducted within the E.U.
^*** Forest Stewardship Council}

© Written by Manuela Moollan, Sustainability & Impact Consultant