The timber industry in the UK (and this blog) has been focusing mainly on softwoods. Slowly, foresters, wood processors and researchers (including us!) are becoming more interested in using the hardwood resources we are producing. Of course, historically, we did use home-grown hardwoods – but our broadleaf woodlands, and our wood product needs, aren’t the same as they were in the past – and the is the very big influence of timber imports – so we need to approach this from new angles.
Currently, we are using hardwoods mainly for biomass energy production, but there is a large potential to use them in other applications, before they can be used for this purpose in the end of their useful life. Generally the idea of timber is to start with the vision of what type and quality of timber is needed for a product and then adapt the forest to be able to provide that. But since we are starting from new angles – perhaps it is better to think instead about the vision for the type of forest we want, and then adapt the way we use the wood to that.
In the Building from England’s Woodland project we want to scope the potential of home-grown hardwood species for building products, including structural uses and non-structural products with some degree of technical performance. We cannot look at all species that grow in the UK within the three-year project, so we need to find out which species are the most interesting ones to look at. The project and our shortlist of interesting species are described more in detail here.
We have based this shortlist on availability on the one hand, and on what we think is most “interesting”* to research on the other. The big-picture availability of UK hardwoods is projected in Forest Research’s 50-year forecast of hardwood timber availability. But our project is not only focused on timber that is produced in commercial forests, but also in smaller, more scattered resources that might be available today. We might describe those as “undermanaged” or “unmanaged” but we we are referring to is the wide range of forests, woodlands and solitary trees that we have – which are mostly not there because of the wood they will provide, but that could provide wood as an added benefit – or would provide wood if there was a market for it. There might be interesting species that are not amongst the top 10 broadleaf species by forest area, but might be more common as street trees, on estates or in certain areas of the country. If you think we are missing one of these species, please let us know!
We have already had lots of interesting feedback, which helps us to narrow down our species selection. Properly characterising mechanical properties of wood with certainty requires a lot of testing and we think it is better to get a reasonable idea about the properties of few species than getting a very rough guess about the properties of many. The species that are on our shortlist can be roughly divided in three groups (and we will probably narrow the list down to one species from each group):
Very traditional hardwood species – which remain in use
Two hardwood species have longstanding traditional use as structural timber, and thanks to them remaining somewhat used, they can actually be visually graded to EN 338 strength classes under our modern construction products standards framework. But the strength class assignment has not been verified by testing for a very long time, so we are not exactly sure how well it works on our current resource. Since growth conditions have a strong influence on wood properties (and because test standards have changed) we suspect the properties might be a bit different. There doesn’t seem to be any evidence of problems in use – but it is prudent to investigate, and perhaps we can even improve the grading. We want to include one of these species to see if the current assumptions that are made in strength grading (including the calculation of secondary properties and the adjustment of values to different moisture contents) are valid.
Oak (this means sessile and pendunculate oak, but we might also include red oak or other species)
Traditional hardwood species
Other hardwood species that have some traditional use in construction cannot currently be graded and assigned to EN 338 strength classes. Research efforts for some of them are underway in Scandinavia, Italy and other European countries, and with our research we could contribute to a large dataset that can potentially be used for establishing grading assignments. Our dataset might not be big enough to establish a conventional strength grading assignment for the UK, but we will be able to see how well these species fit the mechanical properties profiles we expect from “traditional” hardwoods. We can also verify (or challenge) the standard equations for secondary properties and adjustments. Some of these species have a relatively large availability in the UK, and it is well worth scoping their potential.
Ash (although of course there is ash dieback, meaning this is more of an immediate future need)
Non-traditional (for construction) hardwoods
For some hardwoods we know they will not likely fit the traditional profile we would expect from hardwoods. Their properties might be closer to softwoods, and the latest revision of EN 338 recognises this by allowing hardwoods that are “similar” to softwoods to be assigned to softwood C-classes. Initially, this was established for poplar from certain growth areas, but other species are falling into this category as well. Assigning hardwoods to C-classes also means that the equations for calculating secondary properties and adjustments have been established on mainstream softwoods, and we don’t know how well they work on these species. We want to include at least one of these lower-density species to verify the standard’s assumptions. We also hope to open some doors for hardwoods to be used in typical softwood applications.
Poplar (including aspen)
We could potentially also list lime here.
We didn’t mention walnut – which has a lot of potential from agroforestry approaches – but we think it better to put that one aside as something more sensible for markets like furniture and fittings.
* By studying across this range we hope to make the research “interesting” – that is to say by looking across a wider range we hope be able to make more informed guesses about the species we could not include in the research.