5 Questions for InFutUReWood – the use of timber in the UK

This is a longer version of a post you can find on the InFutUReWood project website. If you want just a summary – head over there.

InFutUReWood (Innovative Design for the Future – Use and Reuse of Wood (Building) Components) will research how easy is it to reuse wood from current buildings, and aims to improve the circular economy.

Below, Marlene Cramer and Dan Ridley-Ellis will try to answer these five questions:
Q1) What is the proportion of timber buildings in the UK?
Q2) Which materials are currently used?
Q3) How is the market situation for recycled wood at the moment?
Q4) Is there a good reason for reusing renewable materials like timber?
Q5) Why do you want to change current grading standards?

Q1) What is the proportion of timber buildings in the UK?

In the recent years, timber as a construction material is becoming more popular, particularly for house construction, but also for other types of buildings.
For new house building, the use of timber frame is rising. In 2016 the market share was 28% and it has long been higher in Scotland (83%) than in England (23%). The market share for timber frame for new non-housing buildings is lower (11%), but there has been considerable (and high profile) rise in the use of Cross Laminated Timber in recent years (see “100 Projects UK CLT” for some great examples).
Current housebuilding rates represent less than 1% of the total housing stock per year. Demolition rates are also low (>0.1% and falling), but there is a high level of effort to improve renovation and retrofit (and also a ~0.1% net increase in housing stock via conversion from formally non-residential buildings). According to the 2015-6 English Housing Survey 20% of the housing stock is more than 100 years old and 20% is less than 40 years old. The median age is about 60 years old. The 2008 English housing survey reported that the vast majority of existing houses are of masonry wall construction. Some 9% of pre-1850 houses were built with a traditional timber frame, but there was little timber use from then on until the rise of factory built timber systems in the 1970s. The median age of timber frame in England is about 40 years old. Only about 2.5% of the total housing stock at the time of the 2008 survey was timber frame. However, irrespective of the type of construction, most houses contain large amounts of wood in floors, internal walls and roofs. Timber trussed rafters have been used for roofs in the UK since the 1960s, and the 2008 survey reports that 93% of the housing stock had pitched roofs. External timber cladding is used on buildings of all construction types, but is not at all common. Where it is used in new construction, there is a high level of use of modified and treated wood.
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Structural Timber Association and Egan Consulting, “Annual survey of UK structural timber markets”, 2017.
Waugh Thistleton Architects and the Softwood Lumber Board of Forestry Innovation Investment, “100 Projects UK CLT”, 2018
National Statistics, “English Housing Survey 2015 to 2016”, 2017
National Statistics, “English Housing Survey 2008: housing stock report”, 2010

See also general housing stock statistics (new build, stock, demolition etc)
England data: https://www.gov.uk/government/collections/net-supply-of-housing
Scotland data: https://www.gov.scot/collections/scottish-house-condition-survey/
Wales data: https://statswales.gov.wales/Catalogue/Housing

Q2) Which materials are currently used?

The dominant method for modern timber construction in the UK is light timber frame construction, which uses a very high proportion of wood-based panel products (particularly OSB, but also panels with high levels of recycled wood) and engineered wood products (particularly I-joists). Most modern timber frame buildings use this in combination with traditional masonry cladding (see here for more info). Cross laminated timber (CLT) is gaining relevance in the construction sector for buildings that would otherwise have used concrete and steel.
The most common woods in modern timber construction are spruce, pine and fir. Most of the wood products are imported from Europe. Oak and Douglas-fir post and beam framing is still used for a small number of buildings. Larch is used but mostly in external cladding rather than structural timber. The UK has long been an importer of timber. The species used in the existing building stock (and where it came from) vary by age, depending on the UK’s trading and political history. This can make identification very difficult in older buildings. More recent buildings, dating from the rise of timber factory production, tend to have timber with markings indicating grade, species and origin, although interpreting these against modern standards is not totally straightforward.
Modern timber buildings contain quite a lot of treated wood – especially preservative treatment of timber in roofs and external walls – but also fire treatments, colours and water repellents. The UK does not routinely mark treated wood. Older buildings may contain types of preservative that are now more restricted in use.
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Sanna, F. “Timber modern methods of construction: a comparative study”, 2018
Hairstans, R. “Mass Timber – an introduction to solid laminate timber systems”, 2018
Forest Research, “Forestry Statistics 2018 – Origin of wood imports”, 2018

Q3) How is the market situation for recycled wood at the moment?

The construction and demolition industry is the main source of waste in the UK. Roughly half of the wood waste generated in the UK results from either the construction sector (offcuts, support structures, overestimated purchase, site reject) or demolition of buildings. Each of these is as big a waste stream as packaging. Of the UK’s wood waste that is reused, about 60% is used for panel production (2008 figures) while the rest ends up as biomass energy source, agricultural products like animal bedding, or is exported. These are long established markets, although biomass energy is a relatively new one. These industries are big enough that they can face wood waste shortage issues.
Wood from demolition sites poses particular problems since some of it is treated, covered with paint or lacquers, or otherwise contaminated. Even clean, quality, timber is mixed in with other materials. Most of the treated wood and wood panels recovered from demolition sites end up as landfill or are used for thermal energy production. The good news is that the share of wood that terminates its life in landfill has been decreasing in the last years. This is partly still an effect of the economic crisis, but also partly caused by initiatives like “halving waste to landfill” and “Zero waste Scotland”. Many small scale projects exist to give waste wood a second life as valuable products like architectural salvage, furniture or art objects or to enable its direct reuse in the same function.
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Wrap, Pöyry and Oxford Economics, “Wood Waste Market in the UK”, 2019
Wrap, “Waste wood end markets”
Wood Recyclers Association, “Export of waste wood products decrease as UK markets grow”, 2018

Q4) Is there a good reason for reusing renewable materials like timber?

When architects, consultants and merchants are asked about the benefits of timber in construction, sustainability is ranked the highest. But of course timber is not automatically “sustainable”. Indeed, simple methods such as counting the amount of timber used and converting it into sequestered CO2 create incentives for some kinds of unsustainable use. Aside from the arguments that we should not be counting already sequestered carbon like this, we also need to remember that there is a finite supply of timber.
Wood, trees and forests have been centre stage in the sustainability movement since the very beginning and the modern industry has many examples of good practice. Efforts continue to make construction timber more sustainable than other materials – with due regard to sustainable practice at all levels from forestry to processing to construction – including use of energy, chemicals, long life design and material efficiency. But many factors that contribute to the environmental and social footprint of timber products are far from optimised. Even though the UK might be better off than other countries regarding regulations and certifications of forest products, we need to go a few steps further in the future. Some 64% of sawmill roundwood consumption in the UK is certified (2018 figure), but the sustainability criteria for the basic certificate are not very specific. It is mandatory to “ensure that harm to ecosystems is minimised” in order to obtain the certificate, but the impact on the environment is not necessarily positive with this approach.
Furthermore, a sustainable use of resources includes not to use more than what can be grown (a 70% utilisation rate is recommended). The UK is heavily dependent on wood imports from Europe since its forest area is relatively small. Even so, a lot of timber is harvested locally and it is desirable to increase the share of locally sourced wood to save transport costs and emissions, and give economic incentives to look after the forests.
In the future, the demand for timber is projected to rise and in the coming years the harvest might even be greater than the regrowth. With a rising world population and expanding share of timber buildings in the UK, that can only mean we need to aim for a circular economy and look for alternative resources. And even though timber is already one of these alternative, “renewable” resources, we need to step back and ask ourselves: Can we grow enough timber to satisfy our needs in the future? And is timber really still sustainable if we have to compromise on the other valuable functions of our forests? Since we do not dare to answer these questions with a confident “Yes!” better reuse and recycling are inevitably needed for “renewable” materials. We must not forget that renewable does not mean infinite. We need to act as if wood is a limited resource, because – at any point in time – that is exactly what it is.
Following principles of the circular economy for wood products will release the pressure for productivity on the forest, due to a lower demand. Thus, the many other valuable roles of forests can be enhanced – from natural wildlife habitats to social benefits.
With the same goals in mind, the currently underused species and timber from undermanaged forests are also in the focus of InFutUReWood. At the moment, half of Great Britain’s softwood in forests is (non-native) Sitka spruce. Only 7% of timber harvested in the UK is hardwood and 84% of this is used for biomass fuel, even though a structural use might be possible. If grading methods for these wood species existed, they might become more relevant for the construction sector. And, the use of more diverse timber sources has multiple advantages: On the one hand the introduction of currently uncommon species into the wood chain could mean a shift from monocultures to a more diverse forest, with species and forest management practices more favoured by the public. A system that uses various tree species (and trees of different ages) is more resistant to extreme weather conditions, pests and diseases. In addition it enriches the biodiversity because it forms a valuable habitat for many animals, plants and fungi. Beneficiaries of this change would be the ecosystem, the soil and climate, and last but not least the people.
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Timber Media, “Survey by Södra Wood shows growing move towards timber in the UK”, 2019
Forest Research, “Forestry Statistics 2019”, 2019
Egan Consulting, “CTI Policy Report: Value & Growth Mapping UK Timber Industries”, 2016.

Q5) Why do you want to change current grading standards?

First of all, no proper strength grading rules exist for recovered timber and it is not possible to just use the ones for new timber, since a lot of vital background information is needed to apply them. For recovered timber it is very likely that you have little or no information on species, growth area origin, or previous grading – but all these factors influence its properties and how it should be strength graded. If you can’t make a good estimate about the strength of a piece of timber, you can’t use it in construction as structural timber. This is why we need to develop a grading method for the reuse of timber – one that is compatible with the system for new timber.
Secondly, even though spruce, pine, larch and other softwoods are growing in the UK, 84% of the sawn softwood used in construction in the UK is imported (2016 figure). Unfortunately, the British softwoods are commonly regarded as inferior to timber from the European mainland. And indeed, most of the softwood in the UK is graded as C16 and that is a lower strength class than C24 which is the usual strength class of imported softwoods. And at times of high availability there might not be a price difference between products from these strength classes, so who wouldn’t rather choose the “superior” timber? In reality, strength classes are not as distinct as they are commonly believed to be – C16 and C24 have a significant overlap. A beam that is marked as C16 might well be stronger than one as marked C24. More importantly, C16 has perfectly adequate properties for most kinds of normal construction. Specifying C24 when C16 will do the job does not help sustainability – over-specification is an ongoing problem. It also restricts home grown timber to markets like fences and packaging (27% and 30% of the home grown market, respectively), which are important – but have lower economic value, and shorter lives, than construction timber.
In this project, the grading of recovered wood and alternative timber sources is in focus, but the discussion about grading methods with colleagues, industry partners and designers is not limited to this scope. The aim of the project includes the improvement of current grading standards and encourages rethinking of outdated practices regarding different aspects of construction with timber.
Lastly, as outlined above, it is desirable to change conventional forestry management practices in the UK to more sustainable ones, that fit better against the other roles that forests have. Silviculture practices have a great influence on the wood properties, so if you change them you might also need to update the grading rules. The same applies for changes in climate – temperature, wind and rain. Perhaps most pressing, the accelerating progress in tree breeding and improvement has the potential to change the relationships we assume for grading. We need to go back and look again at studies from decades ago. It seems not only the material flow should be circular, but also our work on improving the grading standards.
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Egan Consulting, “CTI Policy Report: Value & Growth Mapping UK Timber Industries”, 2016.