What is C-CLT?
C-CLT stands for Circular Cross Laminated Timber. It is a circular version of CLT in which secondary timber, such as reclaimed wood or residual timber, is processed into solid timber panels.
Like conventional CLT, C-CLT is built up from several timber layers that are bonded crosswise. This creates a strong and stable panel that may be suitable for walls, floors, roof elements or other building components, depending on performance, certification and project requirements.
The key difference is the source of the material. C-CLT gives wood that might otherwise become a low-value waste stream a new role as a circular building product. It shifts timber from downcycling towards higher-value reuse in architecture and construction.
C-CLT is especially relevant for clients who are working towards:
- circular architecture
- low carbon design
- biobased construction
- reduced embodied carbon
- reuse of existing building materials
- net zero development
- material passports and traceable resources
- more transparent construction supply chains
From waste wood to circular building material
The strength of C-CLT lies in the process. Secondary timber cannot simply be placed back into a building and treated as a high-performance construction product. It must be checked, cleaned, graded, processed and documented with care.
In the development process, secondary timber is first scanned for nails, strength and irregularities. It is then processed by robots: nails are removed, knots are cut out and the timber is trimmed to size. Approved timber is sorted, finger-jointed, planed and prepared for panel production.
The boards are then laid into a vacuum table, bonded layer by layer and pressed into panels. CNC milling can create openings, slots and holes, with the table able to tilt and mill on both sides. Finally, the panels are prepared for transport and fitted with a chip containing information such as timber type, origin, strength, CE marking and certificates.
This makes C-CLT more than a recycled board. It becomes a traceable circular building product, where origin, performance and future reuse are part of the material story.
Why C-CLT matters for circular timber construction
Construction uses vast quantities of new materials. At the same time, large amounts of timber are released from demolition, refurbishment, temporary structures, pallets and industrial waste streams. Too much of this wood is still used at a low value, even when it may have greater potential.
C-CLT changes that mindset. It treats secondary timber not as waste, but as a resource for the next generation of timber construction.
That matters for three reasons.
First, C-CLT can reduce demand for new raw materials. By reusing existing timber, material value stays in circulation for longer.
Second, C-CLT can support lower embodied carbon. Timber stores carbon, and extending the life of existing timber keeps that value within the built environment.
Third, C-CLT makes circularity visible and practical. It turns a sustainability ambition into a tangible building material with a clear origin, process and potential application.
For clients already considering mass timber, C-CLT is a logical next step. Our work as a CLT architect connects material innovation with spatial quality, technical coordination and deliverable design.
The role of Urban Climate Architects
Urban Climate Architects brings C-CLT from research into architectural thinking. We see material innovation not as something that sits outside the design process, but as something that should shape the brief from the beginning.
C-CLT raises important design questions:
- where can circular timber be used safely and intelligently?
- which performance requirements apply to walls, floors or panels?
- how does the material affect layout, spans, detailing and logistics?
- what information needs to be recorded for future reuse?
- how does C-CLT contribute to embodied carbon and low carbon design goals?
- how can the building remain adaptable, demountable and legible over time?
By asking these questions early, C-CLT becomes more than a material experiment. It becomes part of a strong architectural strategy.
C-CLT in collaboration with TNO
Urban Climate Architects is working with TNO on the development and potential application of C-CLT. The research focuses on how secondary timber can be transformed into a circular form of CLT, creating new possibilities for biobased and circular construction.
This collaboration is important because circular architecture needs more than good intentions. It needs reliable processes, measurable performance, material traceability and building systems that can be tested and scaled.
C-CLT brings together three essential areas:
- research and material technology
- architectural design and spatial quality
- practical application in the construction sector
For Urban Climate Architects, that connection is central. We want circular construction to become not only technically possible, but also beautiful, healthy and scalable.
Where can C-CLT be used?
C-CLT may be relevant for a range of building applications. These could include internal walls, partition walls, floor elements, roof elements or other panels where circular timber can take on a higher-value role.
The exact application depends on material performance, certification, fire strategy, acoustic requirements, moisture conditions, detailing and regulation. Every project needs a careful assessment.
Potential applications include:
- circular internal walls
- solid timber partition elements
- floor or roof panels
- retrofit and transformation projects
- timber rooftop extensions
- public buildings with circular material ambitions
- experimental or innovation-led timber projects
- low carbon housing prototypes
C-CLT could be especially interesting for retrofit and rooftop extension projects, where light construction, reduced material use and longer building lifespans are already central to the brief.
C-CLT, cost and feasibility
C-CLT is an innovative material, which means cost and feasibility need to be assessed carefully for each project. The price is shaped not only by the panel itself, but also by the availability of secondary timber, sorting, processing, certification, production, detailing and assembly.
With circular materials, the business case is wider than product cost alone. C-CLT can create value through:
- reduced use of primary resources
- lower environmental impact
- a stronger response to circular procurement requirements
- traceable material flows
- visible sustainability value
- potential future reuse
- a clearer low carbon project narrative
For clients who want to understand the wider economics of timber construction, our guide to the cost of timber construction is a useful starting point. It explains how design decisions, structural systems, programme and delivery affect total project value.
C-CLT and the circular construction challenge
The circular construction challenge is not only about producing less waste. It is about changing how we understand value. Materials should not disappear from the chain after one use; they should remain available for high-quality future applications.
C-CLT fits directly into that shift. Waste wood becomes a building material again. Residual streams become design resources. Buildings become temporary stores of valuable material.
This requires an architectural approach in which design, material passports, detailing, disassembly and future reuse are considered together. Circularity does not begin at the end of a building’s life. It begins with the first design decision.
That is why we connect C-CLT with wider themes such as:
- circular retrofit
- reuse of building materials
- biobased construction
- mass timber
- demountable detailing
- material passports
- urban densification
- climate-responsive design
C-CLT is therefore not just a product. It is a building block for a different way of designing.
C-CLT versus conventional CLT
Conventional CLT is usually produced from new timber. C-CLT uses secondary timber as its starting point. Both systems are based on cross-laminated timber layers, but their circular value is different.
Conventional CLT is already powerful for biobased construction, faster assembly and reduced embodied carbon. C-CLT adds another layer: it extends the life of existing timber and reduces the need for new raw materials.
The choice between conventional CLT and C-CLT depends on availability, certification, performance requirements, structural logic and project ambition. In some projects, conventional CLT will remain the right answer. In others, C-CLT may help turn circular ambitions into something tangible and measurable.
For a wider material comparison, our guide to timber vs concrete can help clients assess carbon, weight, programme, circularity and long-term value.
Who is C-CLT relevant for?
C-CLT is especially relevant for clients who want sustainability to be visible, measurable and embedded in material choices.
For local authorities, C-CLT can help turn circular policy ambitions into tangible public buildings, pilot projects and procurement requirements.
For developers, C-CLT offers a way to position projects around carbon reduction, circularity and material innovation.
For housing associations, it may be relevant for retrofit, rooftop extensions and future-ready housing where material impact and long-term value matter.
For public clients, C-CLT can support procurement processes where reuse, biobased materials, traceability and measurable environmental performance are becoming increasingly important.
If you are preparing a circular or biobased brief, Urban Climate Architects can also support you as a sustainable architect for procurement, helping translate material innovation into clear and deliverable project criteria.
Project case: turning waste wood into circular building material
Challenge
The construction sector uses large amounts of new material, while existing timber streams are often reused at a low value or leave the building chain too early.
Approach
Urban Climate Architects and TNO are exploring how secondary timber can be processed into C-CLT: a circular mass timber panel with potential building applications. The process includes scanning, robotic processing, sorting, finger-jointing, planing, bonding, pressing, CNC milling and digital documentation of origin and performance.
Result
C-CLT shows how waste wood can return to construction as a circular building material. It opens a new route for biobased construction, circular design and reducing demand for primary material streams.
Project link
Add the internal project link here:/en/projects/research-waste-wood-becomes-circular-building-material-urban-climate-architects-and-tno-develop-c-clt
