Timber Accelerator Hub                            SBE0029

Written evidence from the Timber Accelerator Hub

The Timber Accelerator Hub (TAH) is a new cross-industry initiative being hosted by the Alliance for Sustainable Building Products, in partnership with the Laudes Foundation, the Mass Timber Know How Group, Swedish Wood, Timber Development UK (TDUK), Wood Knowledge Wales (WKW), the Structural Timber Association (STA), the British Woodworking Federation (BWF) and Wood for Good. The TAH aims to coordinate industry action to identify and overcome barriers to the wider use of mass timber construction in the UK. We welcome the initiative shown by the Environmental Audit Committee in launching this inquiry.

Part 1. Q1 To what extent have the Climate Change Committee’s recommendations on decarbonizing the structural fabric of new homes been met.

Despite the progress made in decarbonizing the operational energy use of new buildings post-completion, efforts to decarbonize the structural fabric of new homes have made no measurable progress. In fact, the embodied carbon emissions of new buildings have been slowly increasing over time, both in the UK[1] as well as across Europe[2]. Leading experts Jannik Giesekam and Francesco Pomponi describe a ‘substantial gap between the targets and reality’.

In part this is due to several barriers and obstacles that prevent timber being use being scaled up across the UK construction sector. The CCC’s UK housing: Fit for the future? and Biomass in a low-carbon economy reports specifically call for more timber in construction, and recommend the Government introduce policy to support this. However significant obstacles remain, and a lack of incentives persists, preventing the uptake of Mass Timber structural products and impacting the use of timber as a construction material more generally.

Mass Timber is the name for the group of engineered wood products that includes Cross Laminated Timber (CLT), Glue-Laminated timber beams (Glulam), Dowel Laminated Timber (DLT)[3] & Laminated Veneer Lumber (LVL). This type of structural product represents the primary low-carbon alternative to concrete and steel, both of which can be thought of as high-carbon materials due to the industrial processes that currently go into their production (this is outlined further in Part 2 below).

Lightweight Timber Frame, as differentiated from Mass Timber, is well established as a structural material, and was used for 28.4% of UK homes in 2017[4] predominantly for developments of 2-3 story housing. However, this is not incentivized and TAH stakeholders report that its use is being hit with the fallout from Grenfell Tower, with clients moving away from timber frame and insurers increasing premiums. Greater London Authority Affordable Homes Program Funding Guidance 2021-2026 excludes the use of timber frame for housing of any scale.[5]

Mass Timber on the other hand is relatively innovative and allows taller buildings to be constructed with timber as the primary structural material. After a period in which the UK has led innovation in Mass Timber structures (there have been around 1000 completed CLT buildings in the first two decades of the millennium, 300 of these constructed by a single company[6]), the wider uptake of Mass Timber in the UK has been reversed in the years since 2017, thereby limiting developer’s capacity to reduce carbon emissions associated with the structural fabric of their proposals.

Our response to this inquiry will highlight the barriers that Mass Timber is facing, as well as highlighting some of the missed opportunities in the regulatory framework that governs the built environment.

Barrier 1: Fire & Authorities

Building Regulations changes from 2018-2021 have rightly focused on increasing building safety after the tragedy of Grenfell Tower in 2017. The 2018 ban on combustible materials in the external walls of residential buildings with a floor above 18m was brought in to help avoid another such disaster. The ban has prevented the use of mass timber as a structural material in many developments. The 2020 consultation to further lower the ban to 11m may rule out mass timber on still more developments. The impact of this ban has been wider than the intended category of medium to high rise residential buildings, with buildings of other typologies impacted by the greater perceived risk of timber due to its combustibility. [See ‘Insurance’ below]

A prime example of the effect these regulations have had on housing was seen in February 2020 when Newham Council’s housing company swapped the primary structure of one of its developments from timber to concrete in direct response to these regulation changes, thereby increasing carbon emissions. Alex de Rijke, director at the architectural firm dRMM, who worked on the early stages and gained planning permission for the timber building, explains “It was perfectly possible to comply with the building regulations by placing the timber structure inboard of the façade zone.However, dRMM were not appointed to carry out the technical stages of the project. [7]

It is important to acknowledge that mass timber products are combustible, and that they can add fuel to a fire. As such there are understandable concerns around its use. However, in response to the combustible materials ban a significant amount of work is being undertaken to demonstrate the safety of Mass Timber products, funded primarily by the timber industry. This includes several large-scale fire tests being carried out by the Structural Timber Association (STA) in Poland, Arup in France & the Research Institute of Sweden (RISE). It is vitally important that the safety of Mass Timber is demonstrated, and there is a clear role for Government to support this process.

When designed and built by practitioners and professionals with a high degree of competency and experience in mass timber structures, fire risk is managed and mitigated in the same way that fire risk is managed in buildings where steel and concrete is the primary structure. The Structural Timber Association’s Fire Safety in Use Guidance” provides a good reference point.[8]

With regards to fire & building control, there are several opportunities Government could take to intervene and support the development of Mass Timber products as a safe, predictable & low-carbon structural solution.


Barrier 2: Insurance

The Grenfell Tower fire, the cladding scandal and the ban on combustibles materials have sent shockwaves through the property insurance market. With ongoing uncertainty surrounding how many existing buildings have incorrectly installed cladding and an increase in the number of large claims being made due to defective construction not limited to cladding, the known and perceived risks are greatly inflated. This has led to a dramatic increase in premiums and in many cases, cover being removed completely. These market dynamics have inadvertently led to the increased use of high-carbon materials such as concrete or steel instead of low-carbon Mass Timber, as there is more certainty around their properties and performance.

In conversation with British Land, we recently learnt that 6 of their developments had recently been flipped from mass timber to concrete or steel due to the lack of available insurance for both construction and post-completion, therefore greatly increasing the embodied carbon emissions associated with the structural fabric of the developments. 

At an industry-leading forum convened by cost consultants Gardiner & Theobald throughout 2020 & 2021, the ‘Mass Timber Office Forum’, more than 100 expert participants from across the industry participated to identify the greatest barriers to the use of mass timber. Insurance was identified as being the number one barrier, closely followed by fire risk.[9]

The challenge is manifold but has its basis in the context of a hardening insurance market in recent years. Premiums have been rising due to an increase in construction claims globally and many if not all insurers have been de-risking their portfolios. Insurers poor perception of mass timber as a risk is based on several factors and assumptions.

These factors have combined to dramatically increase insurance premiums for all risks, but also an increasing resistance to provide even basic cover for structural timber buildings, notwithstanding a select few cases. Currently, there is no consistent viable insurance solution.

This situation is leading to emissions reductions being prevented, with regards to the structural fabric of new buildings specifically, as concrete and steel are prioritised. This is despite the fact that the risks can be managed and mitigated through high levels of competency in design and construction.

Part 2. Q2 How can materials be employed to reduce the carbon impact of new buildings, including efficient heating and cooling, and which materials are most effective at reducing embodied carbon?


When assessing the embodied carbon emissions of new buildings, the greatest share of these is caused by the construction of the ‘superstructure’. The independent London Energy Transformation Initiative (LETI) have demonstrated this to be 46% of a medium scale residential development’s embodied emissions, or 48% of an office’s embodied emissions[10]. For medium scale building and above, the superstructure of a building is usually concrete frame, steel frame with precast concrete floors. Smaller developments are typically of ‘traditional’ masonry construction (blockwork) or lightweight timber frame as standard.


Mass Timber provides the primary low-carbon alternative to concrete or steel structures. This is due to 4 factors:


Sequestration – Trees absorb carbon from the atmosphere as they grow. The APPG for the timber industries has estimated that if 270,000 houses were built from timber each year, 3m tonnes of CO2e would be sequestered and stored in the structural fabric of these homes.[11]

Storage – The sequestered carbon is ‘locked’ into the structural fabric of the building for the entire lifespan of that building. When assessing whole lifecycle carbon emissions, a building’s lifespan is typically assumed at 60 or 120 years. Buildings often last a lot longer than this.

Substitution – In addition to the carbon benefit from sequestration, carbon emissions are avoided through the substitution of concrete or steel. Steel production necessitates the use of hugely polluting coking coal[12] whilst cement manufacture involves the burning of fossil gas to reach the required temperatures[13], with CO2 produced as a by-product[14]. Productive forestry and timber manufacture does involve some emissions[15], but these are less than for steel and concrete. Waugh Thistleton Architects, architect of many CLT buildings around the UK, has calculated that in total, when considering both sequestration and substitution, a reduction of around 45 tonnes of CO2e can be made per dwelling, if using Mass Timber instead of steel or concrete[16]. If the UK were to build just a third of its annual target of 300,000 homes in CLT – this would constitute a reduction of 4.5m tonnes of CO2e.

Sustainability – Carbon savings are only made if harvested trees are replanted. This can be ensured by using recognised forestry standards such as FSC and PEFC. Sustainably certification is mandated for all timber products through the European Union Timber Regulation.


In a 2021 paper published in the journal Structures, a team comprising researchers and engineers from University of Bath & Buro Happold ran a case study comparison of a concrete, steel and timber structure using the ‘Dynamic Life Cycle Assessment’ (DCLA). They concluded that “timber building structures are likely to have smaller short-term climate impacts than concrete and steel equivalents. Over the longer-term, carbon sequestration can further reduce the impact of long-lived timber structures due to replanting and regrowth of harvested trees.” Furthermore, their analysis showed that after 40 years of a timber building structure’s life a cooling effect would be observed as the trees continued to absorb more carbon than was emitted during timber manufacture.[17]


Part 3. Q3 What role can nature-based materials can play in achieving the Government’s net zero ambition?


Mass Timber, and structural timber more generally, can play a huge role in helping the Government to achieve its net zero targets. Productive forests perform a natural carbon capture and storage mechanism, whilst supporting jobs and providing economic benefit as well. Even after taking into consideration the impact of all the lifecycle stages of timber production and manufacture, over 100 years, each hectare of productive forest delivers a carbon benefit of 7.3 tonnes per year due to the sequestered carbon in the timber itself.[18]


However, forest cover in the UK is currently only at 12%, compared to 28% for France, 32% for Germany, and 67% for Sweden.[19] The UK Government has an ambition to increase tree planting across the UK to 30,000 hectares of tree planting per year by 2025, with a recognition that part of this increase must come from investment in the domestic timber industry and increased uptake of ‘home grown forest products.[20]


As a crucial centrepiece of its Net Zero strategy the UK Government should invest in and enable productive forestry and UK manufacturing.


The Home-Grown Homes Project by Wood Knowledge Wales provides a good example of what can be achieved. The project outlined a strategy for how Wales could achieve a just transition to become a high-value forest nation. Led by Powys County Council and funded by Welsh Government and the EU Rural Development Programme, the research project asked the question ‘How could a timber supply chain based on local forestry products support the delivery of low carbon social housing in Wales?’[21] The project produced a briefing note, titled ‘5 essential strategies for an emerging forest nation’, that includes several policy recommendations that could be adopted nationally. These include scaling up high value timber manufacturing, increasing forest area and incentivizing forest management, changing timber sales regulations, and introducing building regulations to minimize embodied carbon.[22] This report has influenced social housing legislation in Wales, which will require all social landlords to calculate embodied carbon of all new developments by 2023.


Part 4. Q4 What role can the planning system, permitted development and building regulations play in delivering a sustainable built environment? How can these policies incentivise developers to use low carbon materials and sustainable design?

The Building Regulations

The Building Regulations have been successful in reducing the impact of operational carbon emissions. They have however neglected to tackle embodied carbon emissions, providing no current incentive for developers to use low carbon materials. We endorse the following recommendations from Architects Climate Action Network[23]:


Planning System:

Whole life-cycle carbon emissions must be tackled at an early stage in a project, which means the planning system has a big role to play. The New London Plan has introduced a policy which will begin to tackle emissions for large developments:

New London Plan SI 2: “Development proposals […] should calculate whole lifecycle carbon emissions through a nationally recognised Whole Life-Cycle Carbon Assessment and demonstrate actions taken to reduce life-cycle carbon emissions.”

Local Authorities around the country could adopt similar policies within their local plans (Manchester & Brighton also have such a policy). The National Planning Policy Framework should also include a requirement for a whole life-cycle carbon assessment to ensure the entire country is covered.

In addition to whole life-cycle carbon policies, Mass Timber could be promoted through local planning policies. This has been trialled by two local authorities. Hackney Council ‘Wood First’ Policy: Hackney Council adopted a preference for sustainable timber construction in 2012. [24] Although this policy is not currently formally adopted, the intention helped transform the borough into world leaders in the use of Mass Timber products such as Cross-Laminated Timber (CLT), with at least 25 completed CLT projects in the borough alone as demonstrated in a 2017 presentation by Hackney’s ex-councillor Vincent Stops[25]. Powys County Council has taken this a step further and developed a ‘Wood Encouragement Policy’ in 2017, forming a partnership with councils and social housing providers to produce an industrial strategy for timber homes and green jobs for Wales; the Home-Grown Homes Partnership.[26]

To reduce end of life emissions related to timber products, the inquiry could consider several policies from the Carbon Neutral Cities Alliance:[27]

Permitted Development

In August 2020, new laws on permitted development rights were brought in through an amendment to the Town and Country Planning Act[28] that allow the demolition of single detached buildings, including purpose-built blocks of flats, offices & light industrial buildings. This has been dubbed the ‘Right to Demolish’[29]. However, as The Architect’s Journal’s ‘RetroFirst’ campaign has highlighted, demolishing a building, and replacing it with a new one entails high energy-consumption.[30] This is almost always the worst option in terms of carbon emissions, a fact which was succinctly summarized by the architect Carl Elefante, former president of the American Institute of Architects, when he said, ‘the greenest building is… one that is already built.’[31]

To create barriers to the energy intensive practice of demolition and rebuild, the August 2020 changes to permitted development rights could be retracted, and a review of pre-existing permitted development rights for demolition of other building types should be undertaken.

Part 5. Q5 What methods account for embodied carbon in buildings and how can this be consistently applied across the sector? & Q6 Should the embodied carbon impact of alternative building materials consider the carbon cost of manufacture and delivery to site, enabling customers to assess the relative impact of imported versus domestically sourced materials?

There is a consensus that environmental impacts of buildings and building products, including embodied carbon emissions, should be assessed across their entire lifecycle. Lifecycle stages are set out in the British Standard BS EN 15978. This framework should be used as the basis for any assessment methodology to ensure consistency across the sector.

Further to this, there is growing understanding that carbon emissions have varying levels of impact depending on at what point along that lifecycle they come. Put simply, carbon emissions caused now will have a greater impact on human society than those that are projected at 60 or 120 years into a building’s life. Those emissions, caused now, contribute towards the current levels of atmospheric carbon that are driving temperature change this century. This is set out by Will Hawkins et al; “For example, increased temperatures are associated with severe heat-waves and extreme weather, the rate of temperature change impacts the ability of ecological and human systems to adapt, and the cumulative effects of increased temperatures are associated with sea level rise.”[32]

To take this into consideration the scientific community has developed the Dynamic Life Cycle Assessment (DLCA) methodology which gives greater weight to those emissions caused at the beginning of a building’s lifecycle, a less weight to end-of-life emissions. The Environmental Audit Committee should refer to the new environmental regulation that is being brought in by France, ‘RE2020’, which mandates that the DCLA methodology is used to assess and report embodied carbon emissions for all new buildings from 2021.[33]

May 2021

[1] Jannik Giesekam and Francesco Pomponi, 2018, Briefing: Embodied carbon dioxide assessment in buildings: guidance and gaps, Proceedings of the Institution of Civil Engineers - Engineering Sustainability 2018 171:7, https://www.icevirtuallibrary.com/doi/full/10.1680/jensu.17.00032

[2] Martin Röck, Marcella Ruschi Mendes Saade, Maria Balouktsi, Freja Nygaard Rasmussen, Harpa Birgisdottir, Rolf Frischknecht, Guillaume Habert, Thomas Lützkendorf, Alexander Passer, 2020, Embodied GHG emissions of buildings – The hidden challenge for effective climate change mitigation, Applied Energy, Volume 258, https://www.sciencedirect.com/science/article/pii/S0306261919317945?via%3Dihub

[3] DLT is sometimes referred to as Brettstapel, which avoids the use of glues and was first developed as a flooring in grain stores in the US, known at the time as a fire-resistant floor. http://www.brettstapel.org/Brettstapel/What_is_it.html

[4] Structural Timber Association, 2017, Annual Survey of UK Structural Timber Markets accessed via  http://www.forestryscotland.com/media/370371/annual%20survey%20of%20uk%20structural%20timber%20markets%202016.pdf

[5] Mayor of London, 2021, Homes for Londoners: Affordable Homes Programme 2021-2026 accessed via https://www.london.gov.uk/sites/default/files/201123_homes_for_londoners_-_affordable_homes_programme_2021-2026_-_funding_guidance_fa.pdf

[6] Eurban are a leading contractor of CLT buildings, completing their 300th building in 2018 http://www.eurban.co.uk/about-us/company-history/

[7] The Architects Journal, 2020, Newham hires architect to replace timber with concrete on dRMM scheme. Accessed via: https://www.architectsjournal.co.uk/news/newham-hires-architect-to-replace-timber-with-concrete-on-drmm-scheme

[8] Structural Timber Association, 2020, Fire Safety in Use Guidance. Available via: https://www.structuraltimber.co.uk/library

[9] Gardiner & Theobald, 2020, Mass Timber Forum for Commercial Offices https://review.gardiner.com/stories/mass-timber-forum-for-commercial-offices

[10] London Energy Transformation Initiative, 2020, Embodied Carbon Primer. Accessed via: https://www.leti.london/ecp

[11] All Party Parliamentary Group for the Timber Industries, 2018, How the Timber Industries Can Solve the Housing Crisis

[12] West Cumbria Mining plans to mine coking coal, which are currently being reviewed by Robert Jenrick https://www.westcumbriamining.com/what-is-the-plan/what-is-coking-coal/

[13] Cemex – How Cement Is Made https://www.cemex.co.uk/cement-production-process.aspx

[14] Carbon Brief – Why Cement Emissions Matter for Climate Change https://www.carbonbrief.org/qa-why-cement-emissions-matter-for-climate-change 

[15] Forest Research – Greenhouse Gases & Carbon Dynamics of Forestry https://www.forestresearch.gov.uk/research/forestry-and-climate-change-mitigation/greenhouse-gases-and-carbon-dynamics-of-forestry/

[16] Waugh Thistleton Architects – Horizon 2020 research https://waughthistleton.com/news/19/10/14/how-build-wood/

[17] Will Hawkins, Samuel Cooper, Stephen Allen, Jonathan Roynon, Tim Ibell. Embodied Carbon Assessment using a dynamic climate model: Case-study comparison of a concrete, steel, and timber building structure. Structures 33 (2021) 90-98. Accessed via: https://www.sciencedirect.com/science/article/abs/pii/S2352012420307323

[18] Confor, 2018, Eskdalemuir Carbon Report. A study commissioned by Confor of the whole lifecycle carbon benefit of a timber-producing forest. Accessed via https://www.confor.org.uk/news/latest-news/eskdalemuir-carbon-report/

[19] Forestry Commission, 2009, Combating Climate Change: A Role for UK Forests. Accessed via https://www.forestresearch.gov.uk/documents/2062/SynthesisUKAssessmentfinal.pdf

[20] Department for Environment Food & Rural Affairs, 2020, England Tree Strategy Consultation Document. Accessed via https://consult.defra.gov.uk/forestry/england-tree-strategy/supporting_documents/englandtreestrategyconsultationdocument%20%20correctedv1.pdf

[21] Wood Knowledge Wales, Home Grown Homes https://woodknowledge.wales/home-grown-homes

[22] The Home-Grown Homes Project, 5 Essential Strategies for an Emerging Forest Nation. Accessed via https://woodknowledge.wales/wp-content/uploads/2021/03/5_Essential_Strategies_v4.pdf

[23] Architects Climate Action Network, 2021, The Carbon Footprint of Construction, accessed via https://www.architectscan.org/embodiedcarbon

[24] Construction Manager Magazine, reporting on Hackney Council’s ‘Wood First’ Policy https://constructionmanagermagazine.com/hackney-clarifies-wood-first-equal/

[25] Alliance for Sustainable Building Products, presentation from ex-Hackney Councillor Vincent Stops, accessed via https://asbp.org.uk/wp-content/uploads/2017/09/Hackney-Timber-Builds-Vincent-Stops-Hackney-Council.pdf

[26] Wood Knowledge Wales, article on Powys County Council’s Wood Encouragement Policy https://woodknowledge.wales/news/a-pioneering-wood-encouragement-policy-for-powys

[27] Carbon Neutral Cities Alliance, Embodied Carbon Policy Framework accessed via https://carbonneutralcities.org/embodied-carbon-policy-framework/

[28] The Town and Country Planning (General Permitted Development) (England) (Amendment) (No. 3) Order 2020. https://www.legislation.gov.uk/uksi/2020/756/made?view=plain

[29] Charles Russell Speechlys, 2020, Permitted development: a right to demolish & construct new dwellings https://www.charlesrussellspeechlys.com/en/news-and-insights/insights/real-estate/2020/permitted-development-a-right-to-demolish--construct-new-dwellings/

[30] Will Hurst, 2019, Introducing Retrofirst. The Architect’s Journal https://www.architectsjournal.co.uk/news/introducing-retrofirst-a-new-aj-campaign-championing-reuse-in-the-built-environment?blocktitle=retrofirst&contentid=23491

[31] Carl Elefante, 2012, The Greenest Building Is... One That Is Already Built. Forum Journal 27(1), 62-72. https://www.muse.jhu.edu/article/494514.

[32] Will Hawkins, Samuel Cooper, Stephen Allen, Jonathan Roynon, Tim Ibell. Embodied Carbon Assessment using a dynamic climate model: Case-study comparison of a concrete, steel, and timber building structure. Structures 33 (2021) 90-98. Accessed via: https://www.sciencedirect.com/science/article/abs/pii/S2352012420307323

[33] La Cerema & The Ministry of Ecological Transition, 2021, Réglementation Environnementale 2020 : quelles définitions et quels objectifs pour le volet environnemental ? Accessed via: (in French) https://www.cerema.fr/fr/actualites/reglementation-environnementale-2020-quelles-definitions?folder=8182