Since the beginning of human history, we have been building in timber, yet this has largely been at a domestic scale and within a suburban context. In the twentieth-century timber was almost entirely excluded as a choice of primary structural framing, with larger commercial developments utterly dominated by concrete and steel-framed structures. However, in the past 10-15 years, notable shifts in market trends are converging, to elevate structural timber to not only compete with, but potentially overtake, its more institutionally established rivals.
The primary driver is the absolute necessity to substantially reduce greenhouse gas emissions through our construction activity if we are to slow global warming and prevent an environmental catastrophe. Reforistation and use of timber in place of more carbon-intensive structural materials is our best chance, as not only is it renewable but it captures and stores carbon as it grows.
Fundamentally, tenants and end-users fuel commercial markets, and at this point in time they are more educated and invested than they’ve ever been, both recognising and subsequently seeking sustainable attributes in the buildings they occupy. In addition to the environmental advantages offered, exposed timber also comes with many other benefits for occupiers, such as its natural beauty, texture, smell(!) and established biophilic properties that promote healthier living and wellbeing.
Sadly, at a point where usage of structural timber was growing exponentially in the mid to high-rise residential sector, recent and frankly unintelligent changes to the Building Regulations banning combustibles within external walls – a sledgehammer to crack a nut - has instead led to its almost total demise in this sector. However, with innovative solutions under development to address these restrictions we suspect this will re-emerge like a phoenix from the flames, but for now continues to remain a sleeping giant…
On the flip side, the use of structural timber within larger office developments, which remain unaffected by legislative changes, is positively booming.
As a commercial structural engineering practice working with the best clients and architects in the UK, and with an extensive portfolio of commercial timber frame projects, HTS is perfectly placed to observe this growth, which has perhaps doubled or even tripled each year for the last three or four years. We currently have around 30-40 office projects, including 10 projects of over 100,000sqft, either in design or on site and using timber or timber-hybrid framing as the primary structural material.
And there’s certainly enough material capacity, with 43% of land area in the EU wooded, representing only 5% of the world’s forests. This equates to around 27 billion m3 of growing stock, which increases annually at over 700 million m3, yet only two thirds of this growth is harvested for industry and only 1.2 million m3 goes into CLT production. Nonetheless, this is still substantially more than the EU currently uses, and so the surplus is exported overseas.
Of course, there are technical challenges and commercial counterpoints that mean the future is not yet plain sailing for engineered timber. Nevertheless, the industry is rising to the challenge, through increasing investment into research and innovation, and a better all-round understanding.
Timber is combustible, yet as it burns the outer surface chars, protecting the core section to give time for occupiers to escape. Fire engineering in timber structures is a specialist area, and competency is critical to enable refined solutions whilst ensuring ultimate safety. In response to increasing legislative and third-party scrutiny (e.g. London Fire Brigade, insurers), ongoing testing and complex computational modelling now supplement other mitigation measures (e.g. sprinklers, detection, means of escape), to demonstrate auto-extinction and provide the necessary reassurances.
Although largely a benefit of CLT slabs, reduced self-weight leads to reduced airborne sound separation, necessitating additional mass (typically cement boards) to be reintroduced into floors to counter this. However, these can be tuned such that these floors are still lighter than concrete alternatives encumbered with an over-provision of mass.
Yet despite emerging solutions to perceived technical challenges, perhaps our biggest obstacle is ourselves and the comfort-zone within which we are wrapped. To demonstrate the commercial and economic value that we know structural timber can bring, we often go to the market ourselves to get early-stage costs, and analyse programme or substructure savings, as the full extent of commercial viability of timber reaches beyond the framing package alone. It is this proactive approach which has seen the realisation of a number of our most successful projects.
In order to respond, we have created the HTS Timber Focus Group, dedicated to harvesting our knowledge, filtering the lessons learned and sharing them across our 130 person-strong practice. We have also embarked upon a programme of related self-funded research we call HTS+, where for example we have completed full-scale testing of composite fixings between CLT slabs and glulam beams, allowing significant reductions in material usage.
Another HTS+ development is our Carbon Counter, a Revit plug-in which allows us to measure and then communicate the carbon cost of different structural materials to clients and collaborators. Used across every stage of a project, from concept to completion, the tool has been instrumental in the delivery of a number of our low-carbon timber-framed workplaces.
Using processes akin to evolutionary natural selection, as design pioneers we are systematically attacking the weakest links in timber structures, finding solutions or (if necessary) compromises until the next issue governs, upon which we move on again with the fine-tuning. These are exciting times, where knowledge growth is fast, and opportunity to innovate is abundant.
We should not fear the unknown, we should look to better understand, and those of us who already know need to better educate. There is no need to exaggerate the facts or spin the truth. Engineered timber must speak for itself and justify its own existence, warts and all.Now is not the time to work in silos or gain commercial advantage through preserving discoveries or realisations.
Now is the time for the construction industry to work as one, share all knowledge and all innovation, make up for past excess and get our house in order. We have an opportunity to prevent a disaster of literal global proportions, and ensure the future is preserved for future generations. And the future is wood.