By Matthew Linegar, Director R&D and Product Management, Building Solutions at Stora Enso

Developers are being asked to resolve a UK housing policy contradiction. On one hand, the UK desperately needs more new homes to address long-term systemic shortages. On the other, the environmental impact of buildings is under the spotlight like never before and green standards are likely to get stricter.

The problem is that standard building design practices are not aligned with environmental requirements. So, as it stands, we can either build our way out of the housing crisis while deepening the environmental one, or address climate change while hampering efforts to build desperately needed new homes.

Then – as if this wasn’t a thorny enough challenge for developers – there is the fact that the upcoming tightening of the combustible cladding ban introduced in December 2018 will likely to remove one of the most promising tools available to resolve this contradiction – engineered timber. Surely, in order to treat the climate crisis with the seriousness it deserves, all options should be on the table?

A rock and a hard place

According to the World Green Building Council, buildings account for 39% of global emissions. This splits into 28% for operation and 11% for embodied carbon from the upfront materials and construction. If we are to sufficiently decarbonise our societies, it is non-negotiable that lower-carbon building materials and methods are necessary – especially if homebuilding is set to approach the 300,000 new homes per year which was outlined in the government’s most recent manifesto. However, mainstream construction materials, are notably carbon-intensive.

The challenge for developers to deliver high volumes of new homes – affordably – while decarbonising, is huge.

Fortunately, there are options available to eco-conscious developers. One of the most promising families of materials is engineered timber.

Engineering a solution

Engineered timber can be thought of as combining the environmental performance of a natural, renewable resource with the performance characteristics of manmade materials. It is, in many ways, the best of both worlds.

From an environmental perspective, engineered timber is a renewable resource. So long as it is harvested strictly from sustainably managed forests, it is possible to plant more trees than are used. Crucially, the trees remove carbon from the atmosphere as they grow and store it away, locking the carbon in the timber for the lifetime of the material. This means that, as long an engineered timber building stands, the material is in effect carbon negative.

But can engineered timber structures provide comparable performance to traditional construction methods? Emphatically yes – provided they are designed correctly. One of the most prominent engineered timber materials, cross-laminated timber (CLT), is fully capable of supporting high-rise structures such as apartment complexes or office buildings.

What’s more, CLT is prefabricated and supports the growing need for more offsite construction to speed up developments.  The lighter weight nature of CLT means fewer site deliveries, reducing costs and the impact on the local community – thereby aiding planning applications. It also means that more units can be built on sites where weight is an issue, such as those above tunnels or with poor ground quality, and it creates opportunities to create more value from existing buildings through vertical extensions. This can help increase returns on the project, deliver more homes and in some cases make the difference between commercial viability and unfeasibility. Furthermore there is growing evidence to suggest that wooden buildings contribute health and wellbeing benefits to their occupants.

Strong and safe

However, it’s important to note that engineered timber is not only strong, but it is also safe. For those unfamiliar with the materials, it is understandable that they would have some concerns over fire safety – after all, wood is a combustible material.

This does not mean that wood is unsafe or should be banned, on the contrary.  But it does mean that developers must appoint competent designers that fully understand the performance of combustible and charring materials to ensure that the design and construction meets or exceeds the requirements of the building regulations.

Of course, building design and our knowledge is not static, and over time we learn more about the fire performance of engineered timber. The industry has a responsibility to invest in continuous development of knowledge and best practice – and the industry welcomes this. For example, we at Stora Enso are leading a special interest group under the Structural Timber Association (STA) together with other leading CLT manufacturers and industry experts to better understand CLT fire compartment behaviour to make it easy for designers to specify.

The question of the day

The immediate question in front of us is not whether engineered timber is a safe building material to use. The answer to that is ‘yes’ – with rigour, diligence and a continued investment in developing best design practice.

The question of the day is whether the time is right to extend the combustible cladding ban to 11m which would further limit the application of CLT. The question is whether – at a time of pressing housing and environmental crises – we can afford to remove the industry’s only scalable renewable and carbon negative option for a structural material.

We argue that the answer to that is ‘no’. The UK is an anomaly as countries around the world scale-up their use of engineered timber, recognising its benefits and advancing best practice. We should expect more of the industry, we should invest in developing knowledge and competency across the sector, and we should hold developers to high standards. We should take an evidence-led approach.

But we should not throw the baby out with the bath water with a ban that threatens to stop the growth of the only renewable construction material. The combustible cladding ban has already caused a reduction in the available market for engineered timber even though the ban only relates to the external wall construction of certain residential type buildings. Perception is clearly stronger than reality. 

If the new consolation is successful and the threshold is reduced further from 18m to 11m then the message to the market will be interpreted as: “engineered timber is off the table”. Is that an acceptable unintended consequence? Not if we expect developers to deliver on the housing and climate crises at the same time.

If there is to be a response to these crises commensurate with their scale, then surely all options must be on the table for developers. Hence, we encourage developers and other stakeholders to respond to the current consultation and to limit the impact of the proposed extension to the combustible cladding ban which includes the structure. After all, we need all our options on the table.