25 March 2020

The impact of material choices

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Photo: Joensuu Lighthouse, Arcadia Oy Arkkitehtitoimisto.


Rory Doak is the UK Business Development Manager for Stora Enso Building Solutions. He is a graduate of Edinburgh Napier University and has a BEng (Hons) Civil Engineering and MSc in Advanced Structural Engineering. He specialises in mass timber and modular construction.


The world is in the midst of a climate emergency and as an industry it is vital that we respond and react accordingly. Our material choices are of great importance, and our approach to sustainability and circularity will drive our response. When we look at the construction industry overall, the idea of circularity can manifest in many ways, from recyclability and waste management to design for deconstruction. However, a key element of circularity is the industry’s ability and commitment to regenerate and replace what it takes.


This is where timber distinguishes itself as a renewable and truly sustainable construction material. As the renewable materials company, Stora Enso operates at the heart of the bioeconomy and contributes to a circular economy. Sustainable forest management secures the availability of our renewable resources, protects biodiversity, and helps combat global warming. Wood and wood products meet the criteria of a circular bioeconomy more than any other construction material, because wood can be re-used, recycled and used as a carbon neutral source of energy at the end of its long lifecycle.


Reaching net zero by 2030

Reaching our urgent net zero targets and reducing our overall CO2 emissions is possible if, as an industry, we consider and embrace, where appropriate, the use of wood for all forms of construction. Why this is so important is that – according to the World Green Building Council – buildings account for 39% of global emissions. Off-site methods of construction that use mass timber products such as CLT and LVL mean that wood is used for an increasingly wide range of building typologies and sectors from workplaces and schools to stadia, theatres and multi-storey residential apartment blocks.


The potential for mass timber construction in the modern world is very strong. As a renewable, lightweight construction material that stores carbon over its lifetime, mass timber is perfectly aligned to allow us to meet urgent net zero targets. However, although wood used in mass timber components will store carbon for the whole life of a building, the majority of carbon is sequestered in the first 30-70 years of growth and maturity of the tree. Therefore, sustainable forest management is a key factor, and it is imperative that wood is sourced from sustainably managed forests with full chain of custody and recognised certification.


An effective waste management strategy is equally important. For example, all residuals produced at Stora Enso’s seventeen sawmills across Europe are formed into pellets used to power three adjacent CLT and LVL manufacturing plants and to generate renewable electricity for homes and businesses in the surrounding areas – and thus making use of the entire log. Mass timber itself is a zero waste product. It is manufactured to millimetre tolerance and is completely integrated into the BIM process where the 3D model defines the accuracy of the material for delivery and installation, rather than relying on traditional workmanship.


The ability to pre-drill and router services in precision factory conditions creates an even closer link between project team and site, which results in buildings that operate as they were designed and ensures that operational carbon can be minimised. An example is CCG’s Yoker Riverside building in Scotland. Installed by mass timber specialist Eurban in 2017 using CLT by Stora Enso, this remains Scotland’s tallest timber building at 7–storeys. In production, the CLT used at Yoker Riverside created 74 tons of CO2 and 75 tons of CO2 in transport; however, the use of CLT for the superstructure removed 907 tons of CO2 from the atmosphere, resulting in a net total of -757 tons of CO2.


Buildings and construction account for more than 35% of global final energy use and nearly 40% of energy-related CO2 emissions. Therefore, producing energy efficient buildings is an essential target, equal in importance to reducing the embodied carbon of the building. This has been achieved at The Lighthouse, a 14-storey student accommodation block in Joensuu, Finland. Currently Finland’s tallest timber building, The Lighthouse uses Stora Enso LVL-G and CLT for the superstructure and incorporates a heat recovery unit which minimises heat lost via wastewater, recovering the energy and using it to heat the apartments.


The manufacturing precision of mass timber components and associated connection design also results in high levels of airtightness. Mass timber’s inherent U-value also helps to form thermally efficient structures when combined with insulation, ideal for use in Passivhaus standard buildings.


The impact on a construction project of material selection is a key consideration for any project team and, given the current climate emergency, there has not been a better time to review material choice and to consider all the implications attributed to each material.