Research – From waste wood to circular building material: Urban Climate Architects and TNO develop Circular CLT (C-CLT)

This research touches on one of the most important questions in the construction sector: do we continue to produce new materials, or do we learn to build smarter with what is already there?

For Urban Climate Architects, circular construction does not start with more material, but with a closer look. At existing buildings. At hidden timber stocks. And above all, at the value of materials that currently disappear from the construction chain far too often.

As timber construction architects , we explore how timber construction, reclaimed building materials, and biobased designs can come together in future-proof architecture. The role of the CLT architect in the Netherlands is also changing as a result: from designing exclusively with new CLT to designing with circular alternatives from existing material streams.

From demolition to harvesting

A building is not an end point. A building is a material bank.

Homes, schools, offices, and commercial buildings contain large quantities of wood that often still have a long life ahead of them. The first step, therefore, is not demolition, but harvesting: carefully dismantling, sorting, and registering what is recovered from a building.

This requires more attention than traditional demolition, but it also yields much more value. Structural timber is preserved, materials are given a second life, and fewer new raw materials are needed.

At the same time, a new circular chain is emerging in which architects, researchers, processors, social enterprises, and construction partners work together.

This is how waste wood is transformed into a valuable raw material for a new generation of buildings.

Not every piece of wood has the same future

Before wood can be used for construction again, we need to know what it is still capable of. Secondary wood is therefore assessed for quality, connections, and structural performance. In doing so, we look at factors such as strength, stiffness, stability, moisture behavior, and reliability.

Not every wooden element needs to have the same destination. Some parts are suitable for high-grade structural applications, while others can be repurposed for finishes, interiors, or panel materials.

It is precisely this careful selection that makes the reuse of building materials reliable.

The goal is not simply to reuse old wood. We want to return as much wood as possible to the construction chain safely, smartly, and at the highest possible value.

This is how trust in circular building materials grows.

Circular CLT: reused wood with structural potential

Circular CLT is built from carefully selected layers of secondary wood. After assessment, processing, and gluing, strong and stable panels are created that can be used in buildings once again.

While traditional CLT is usually produced from new wood, C-CLT gives existing wood a second structural life.

This makes it particularly interesting for clients who want to reduce the use of new raw materials, lower embodied CO₂ emissions, and take a serious approach to a circular construction strategy.

Circular CLT shows that timber construction is not just about choosing a material. It is also about choosing a chain.

Where does the wood come from? How much value does it still hold? And how do we ensure that this value is preserved?

These questions align directly with biobased construction, circular material flows, and low-carbon architecture.

From residual stream to high-quality building material

The process behind Circular CLT clearly demonstrates how circular innovation works in practice.

First, wooden elements are carefully harvested from existing buildings. Next, their quality and structural integrity are assessed. Usable elements are repaired, processed, and assembled into new panels. They then return to the construction sector, for example as wall, floor, or roof elements.

This is not low-grade recycling. This is value retention.

For Urban Climate Architects, this is the core of circular architecture: not just reducing impact, but reactivating existing value.

In this way, a residual stream becomes a building block for sustainable structures, lightweight constructions, and future-proof cities.

The economic aspect also plays an important role here. In many projects, the costs of timber construction are part of the decision-making process. Circular material use therefore requires a smart strategy from the very first design stage: technically feasible, financially realistic, and architecturally strong.

Why this research is important for the construction industry

The Netherlands has relatively few forests, but millions of square meters of existing buildings. Within them lies a vast stock of materials.

Anyone serious about reducing the environmental impact of construction must therefore look not only at new biobased materials, but also at the resources already present in our cities.

Circular CLT is part of that broader systemic change. It connects timber construction, circular building, and urban mining. This allows trees to remain trees for longer, while our built environment continues to evolve.

This makes the research relevant for municipalities, developers, housing associations, and construction partners looking for scalable solutions for sustainable housing, renovation, and urban densification.

When comparing timber construction and concrete this question becomes increasingly relevant. It is not just about which material is technically feasible, but primarily about which material strategy has the lowest environmental impact while retaining as much existing value as possible.

Circular CLT in future projects

C-CLT can be particularly interesting for projects where lightweight construction, low environmental impact, and smart material use converge.

Consider:

■ rooftop extensions
■ transformation of existing buildings
■ circular renovation
■ urban densification
■ new timber construction projects

For rooftop extensions weight often plays a decisive role. Timber structures are significantly lighter than many traditional alternatives. When reclaimed wood can also be used within such a structure, an additional circular layer is created: building on what is already there, with material that already existed.

Circular CLT also aligns strongly with Paris Proof construction. After all, a building's climate impact is determined not only by energy consumption during use, but also by the materials we use to build.

By constructively reusing existing materials, we can further reduce the embodied environmental impact of new buildings.

This makes Circular CLT more than just a material innovation. It becomes a design strategy.

Urban Climate Architects puts research into practice

Urban Climate Architects designs buildings that are lighter, healthier, and circular. Solid wood, biobased materials, and reused building elements play a key role in this.

Through our partnership with TNO, innovations like Circular CLT can be integrated early in the design process.

That is important, because material choices don't start on the construction site. They start at the drawing board.

As architects, we explore how circular timber can contribute to housing, rooftop extensions, building transformations, and new urban living environments. In doing so, we look beyond technical performance to consider spatial quality, health, affordability, and long-term value.

For clients working on circular construction in the Netherlands, sustainable procurement, or innovative timber projects, C-CLT offers a new perspective:

less waste, fewer new raw materials, and more value from what already exists.

The construction of the next century starts with what is already here

Perhaps we have built in only one direction for too long. A new project almost automatically began with new materials, new products, and new raw materials.

The coming century demands a different approach.

Not producing more.
But making better use of what we already have.

Circular CLT makes that shift tangible. Waste wood becomes building material again. Buildings become material banks. And timber that would otherwise be lost is given a high-value future within circular architecture.

For Urban Climate Architects, this innovation does not stand alone. It is part of a broader design vision: creating sustainable buildings with fewer primary raw materials, more biobased and circular materials, and a healthy living environment.

Discover the possibilities of circular timber construction

Are you working on a project, tender, or public assignment where timber construction, circularity, or material innovation plays a key role?

Urban Climate Architects helps you determine the right design and material strategy from the very start.

Discover with us how Circular CLT (C-CLT), biobased construction, reuse of building materials, and circular timber construction can contribute to a future-proof project.

Circular timber construction in practice

For rooftop extensions, renovations, and urban densification, Circular CLT can be an important next step. C-CLT connects reclaimed wood with lightweight, biobased structures, aligning perfectly with our approach to rooftop extensions, circular renovation, and sustainable timber construction.

In this way, waste wood does not mark the end of a building's story, but the beginning of a new structural life cycle.

Read the full TNO publication here.