In recent years there has been a move to construct more sustainable buildings with an emphasis on reducing their environmental impact, write NUI Galway’s Dr Conan O’Ceallaigh, Dr David Gil-Moreno and Prof Annette Harte.
Construction and buildings are responsible for about 39 per cent of all global carbon emissions with about 28 per cent being attributed to operational costs of the building and 11 per cent attributed to the embodied carbon of the construction materials and processes (IGBC – Irish Green Building Council, 2019).
Reducing the impact of construction is essential if we wish to transition to a carbon neutral economy while also accommodating an extra one million people in Ireland, as projected by Project Ireland 2040.
Recent policy updates will ensure that all new buildings in the EU will have significantly lower operation impacts.
The current significant challenge is to address the embodied carbon emissions of construction products used in our buildings.
This has resulted in significant innovation within the construction industry in areas such as product development, lean construction processes and so on.
Timber is a climate-friendly material that has seen a revival within the construction sector in recent years.
It is one of the oldest building materials in the world but its use in large-scale construction was limited in the last century due to the limited availability of resources and particularly large structural sizes to sustain the demands of modern-day construction.
The recent revival of timber is related to significant research and innovation in the timber engineering sector resulting in advances in the production of highly Engineered Wood Products (EWPs) and connection systems, which have allowed this material to rival steel and concrete in large-scale buildings.
Innovation in timber construction
EWPs such as glulam and cross-laminated timber (CLT), formed from multiple layers of timber bonded together, have allowed larger, more dimensionally stable and homogenous elements to be manufactured and shaped into building components with spans far greater than that of sawn timber elements.
CLT, which comprises multiple layers of orthogonally bonded timber laminations, is largely responsible for the rising number of large-scale timber buildings.
Manufactured offsite, CLT panels are particularly suitable for automated computer numerical control (CNC) routing which utilises CAD or BIM object data to produce building components inclusive of door, window or service openings from a master panel.
Once manufactured, the components are transported and quickly assembled on-site, thereby improving project delivery times and reducing labour costs.
Being increasingly utilised around the world
Such products are being increasingly utilised around the world with more and more engineers and architects developing an appreciation and understanding of the material.
Currently the world’s tallest timber building is the 85m-tall Mjøstårnet building in Norway, which was completed in early 2019.
It is an 18-storey mixed-use building constructed with floors and elevator shafts made entirely of CLT panels and columns made of glulam.
Closer to Ireland, in the borough of Hackney in London, the introduction of a ‘Wood First Policy’ in 2012 has resulted in more than 25 large timber buildings being completed.
The policy, introduced to stimulate timber construction as a climate change mitigation strategy, has resulted in school projects, community centres, offices and residential buildings up to 10 storeys tall being built.
‘Dalston Lane’ in Hackney is currently the largest CLT building in the world with 3,852 m3 of CLT used for external, party, core walls, floors and stairs.
In total, it is 33.8m tall and comprises 121 residential units over 10 storeys. The development also takes advantage of the lightweight characteristics of timber due to weight limits associated with the underground metro system in London.
Using lightweight CLT construction rather than concrete allowed the developer to add an additional 15 units with further capacity to add 20 more units in the future.
A key benefit of using timber in construction is not only the low embodied carbon associated with the manufacture of EWPs but also the carbon sequestration or carbon storage capacity of EWPs.
It has been well publicised that forests have an important role to play in climate change mitigation as forests actively remove carbon dioxide for the atmosphere while converting it to wood and releasing oxygen at the same time.
Harvesting the trees before they die naturally locks the carbon into the wood and this remains in EWPs over an extended lifespan. Replanting new trees then begins the cycle of carbon storage again.
Carbon sequestered in such wood-based products can significantly lower a building’s embodied carbon profile. When constructing ‘Dalston Lane’ in Hackney, the design engineers Ramboll estimated that 2,600 tonnes net CO2 are saved in the timber structure (equivalent to taking 520 cars off the road for one year) compared with the equivalent concrete construction.
This wooden building, among many others, not only required less energy to produce but will also store this carbon for decades.
Increasing the number of buildings manufactured from timber will significantly reduce construction-related carbon emissions through a combination of embodied carbon reduction, carbon sequestration, and offsetting carbon emissions associated with equivalent steel and concrete construction.
Research in Ireland
There is significant potential to utilise Irish grown timber in EWPs. The use of timber in added-value products could have both economic and environmental benefits and there are significant opportunities as the roundwood available for production is forecast to increase from four million m3 in 2016 to close to eight million m3 by 2035.
The Timber Engineering Research Group at NUI Galway have been exploring the possibilities of manufacturing glulam and CLT from Irish grown timber and its potential use in construction.
The recently completed ‘Innovation in Irish Timber Usage (IITU)’ and ‘Commercialisation of Irish Cross Laminated Timber (CICLT)’ projects demonstrated the potential to manufacture EWPs from Irish grown C16 grade timber.
Currently, the Wood Properties for Ireland Programme (WoodProps Programme) is ongoing in NUI Galway. WoodProps is a joint programme between the Timber Engineering Research Group at NUI Galway and the Centre for Wood Science and Technology, Edinburgh Napier University.
It is grant-aided by the Forest Sector Development Division of the Department of Agriculture, Food and the Marine and is focused on characterising Irish-grown timber and the use of timber in construction together with the associated work at national and European levels in standardisation for structural timber quality, production and design.
Recently, the WoodProps team launched the online ‘Timber Information Resource Centre‘ a source of collated scholarly and technical documents to inform architects, developers, engineers, product manufacturers, policy makers and other industry stakeholders on all aspects of timber properties, engineering and design.
The database is free to use and designed to be a living database that is updated frequently to keep up to date with a fast-moving and innovative industry.