What exactly is Recycled CLT (ReCLT) , and how did this initiative come about?
Peteris Vasuks: Most people involved in developing the ReCLT technology have a rather extensive experience in the development of woodworking technology and the production and construction of wood-associated building products. By working with glue-laminated timber (glulam) and cross-laminated timber (CLT) production more and more, it became clear to us that people working with prefabricated wood products need a deep and integrated understanding of the whole process, from forest to design, production and on-site assembly.
We encourage smart design: To design buildings with as minimum waste as possible. In an ideal world, we would design buildings with almost no waste. However, in most cases the type of design would potentially cause problems at the building site and make the process less effective. CLT buildings are therefore still designed in a way where we get cut-offs from window and door openings, geometrical cuttings, and component layout optimisation. Since we cannot really avoid waste, we wanted to create a technology that would help not to downgrade the “leftovers” to chip value. We are also thinking about the future: What will happen to the dismantled CLT? Is chipping the only way to reuse the material?
ReCLT offers solution to these issues by keeping the material as close as possible to the initially intended use, whether it is production cut-offs recycled into structurally usable material, or CLT from dismantled high-rise buildings recycled and reused for low-rise construction applications.
How is the belief of “ecology is not possible without economy” embodied in ReCLT?
Vasuks: This was formulated by one of the authors of ReCLT 14-15 years ago: “Ecology and economy are not possible one without the other. Ecology is not possible without economy; ecological solutions need to be affordable for them to be widely applicable and have a noticeable impact on the environment. Economy is not viable on a long run with having a ‘reasonably’ ecological approach.”
CLT, when compared to other traditional building materials, is still more expensive to build with, or depending on many factors it can also be the other way round. Smart use of materials makes CLT more cost efficient in production, and thus more affordable for end users. It is thus easier to switch from conventional building concepts to environmentally friendly solutions. Additionally, Nordic CLT, the company behind ReCLT, not only reprocesses all of its cut-offs from structurally usable materials but also buys them in from other CLT producers. This leaves a positive effect on the production costs of cut-off supplier.
From the collection to the manufacturing aspects, how environmentally friendly is the recycling process?
Vasuks: In most cases, the cut-offs would be chipped and used for energy. In other words, they are reprocessed into lower-added value product. ReCLT offers an alternative approach to avoid downgrading the value of the product. The timber that CLT elements are produced from has been harvested, transported, sawn, dried, finger jointed, planed and glued. CLT cut-offs basically has the same quality product as the element itself. The only difference or fault compared to standard CLT is the lack of universally usable, or effectively CNC machinable dimensions. ReCLT helps to solve this.
Since the cut-offs processes are comparably large, the energy consumption per 1m3 is low. From 1m3 of CLT cut-offs, we get approximately 0.8m3 of recycled CLT, depending on the cut-off size. So, 80% of the cut-offs go back into the long CO2 cycle instead of being chipped and burned.
How are the cut-offs manufactured back into reusable CLT panels, and can you rate the durability and strength of the recycled CLT panels?
Vasuks: Production of recycled CLT consists of multiple formatting, profiling and gluing processes carried out in several cycles depending on the incoming cut-off size and desirable panel size. Most of the cut-offs we reprocess come from doors and windows. There can be as many as 15-16, in average 6-8, cut-offs used to produce one 5m x 3m panel.
In the process of the technology development, tests were carried out. The results from the bending strength testing were approximately 70-80% of the original bending strength of a CLT panel.
ReCLT received the “first order” to design a CLT, glulam and recycled CLT hybrid building. Can you share more that project and other projects that ReCLT will be embarking on? Vasuks: Unfortunately, that project has been postponed due to an overall rise in building costs. Most probably we will get back to it sometime in 2023. It was planned as a 220m2 barn-type, one-family house with the load-bearing part built with glulam beams and 100mm of recycled CLT for the self-loadbearing external walls with insulation and timber-cladded ventilated façade. The partition walls will be built with 100mm recycled CLT, and the slabs with ordinary 140mm CLT.
Some smaller residential projects like country house attachments have been built using 100% recycled CLT, or with it as a combination. Currently, there are a couple of projects in Riga, the capital of Latvia, in discussion where most probably recycled CLT made from cut-offs generated to produce CLT for the same building will be used. Recycled CLT is also used widely for cabin productions, specifically with NordCabin, a producer of cabins based in Latvia.
Lastly, is there anything you would like to add about ReCLT?
Vasuks: Wise use of timber, prefabrication and modularity are keys to a sustainable future. Here are two ways to push environmentally friendly building solutions that have been industrialised to wide markets, especially to make impact in a short term: One would be to tax less environmentally friendly solutions, the other would be to make environmentally friendly solutions more affordable to a wider public. We encourage the second one. We have only made couple of first steps. The endorsement we get from all over the world gives us the energy to carry on and believe we are on the right way. We already have plans to broaden the application possibilities of recycled CLT, and to improve technical properties and visual appearance of the products.
Source: Wood in architecture issue 2 2022/39