By combining careful material assessment, prefabrication, and reversible construction methods, INBUILT shows how timber reuse can become a realistic and scalable solution. Rather than treating buildings as end points for materials, the wall system reframes them as temporary storage for valuable resources. In doing so, we demonstrate how construction can shift from a linear to a circular model, using what already exists to build what comes next.
Natascha Steiner, Researcher, Karlsruhe Institute of Technology (KIT)
Across Europe, millions of tonnes of construction timber are removed from buildings every year. In most cases, this wood is incinerated after just a few decades of use, releasing stored carbon back into the atmosphere and destroying a valuable resource. Within the INBUILT project, Karlsruhe Institute of Technology is testing a different approach: the development of prefabricated external wall elements made entirely from reclaimed timber, designed to meet modern requirements while remaining fully dismountable and reusable. The demonstration bridges research and practice by showing that reclaimed timber can be used not only for interior elements or temporary structures, but as a fully functional part of the building envelope.
Why reclaimed timber?
The building sector is responsible for around 36% of CO₂ emissions in the European Union, with a large share coming from material production and construction activities. Timber has a unique role in this context. Although trees store carbon during growth, this benefit is lost when wood is burned at the end of a building’s life. By contrast, reusing timber extends its carbon storage function and avoids emissions associated with producing new materials. Reclaimed timber from roof structures, floor joists, and wall framing often retains excellent structural quality and performs just as reliably as newly harvested wood.
However, certification and construction methods need to be modified to allow reuse at scale of this valuable resource. For example, reclaimed timber often comes in non-standardised dimensions, making it difficult to integrate into conventional construction processes. Additionally, the lack of harmonised certification standards across Europe means that structural approval must often be obtained on a case-by-case basis, increasing time and cost.
From deconstruction to prefabrication: how reclaimed wood wall systems are designed and assembled
Within INBUILT, reclaimed timber is sourced from local building deconstruction sites, minimising transport distances and supporting regional material cycles. Each batch of wood undergoes a structured process and only timber that meets strict safety and quality criteria is used. Once approved, the reclaimed wood is digitally mapped and processed into prefabricated wall elements at KIT.
These elements combine structure, insulation depth, and connection logic in a single unit, allowing precise fabrication and efficient on-site assembly. Prefabrication also reduces waste, improves quality control, and shortens construction time on site.
A defining feature of the reclaimed-wood wall system is its focus on design for disassembly. Instead of adhesives, foams, or permanent composite layers, the wall elements rely on wood-to-wood connections. These are joined using dowels and digitally fabricated joinery techniques based on traditional carpentry creating stable but reversible connections. At the end of its service life, the components can be separated and reused in future buildings, preserving their material value and avoiding downcycling.
High thermal performance with low environmental impact
The external wall system achieves performance levels that exceed current German building regulations for insulation. Its target U-value of approximately 0.14 W/m²K, means that heat loss in winter is significantly reduced, which is well below what regulation require. However, good insulation is no longer just a winter concern as rising temperatures and more frequent heatwaves place greater demands on indoor comfort. Well-performing wall systems can help stabilise indoor conditions and reduce reliance on air conditioning – an increasingly important consideration for future buildings.
The environmental benefits go well beyond energy efficiency. The wall combines a high share of reused and recycled materials with bio-based insulation products, reducing dependence on energy-intensive mineral and synthetic materials.
The prefabricated reclaimed-wood walls are implemented in the mobile tiny house demonstrator of INBUILT, in Pfeffenhausen (Germany). After construction, the building will be monitored over an extended period, with sensors measuring temperature, humidity, and energy performance. This real-world data will help validate laboratory results and provide evidence of how reclaimed timber systems perform under everyday conditions.
A step towards circular construction, but regulatory changes are needed
The reclaimed-wood external wall system demonstrates that circular construction is not limited by material performance, but by established routines and regulatory frameworks.
To enable widespread adoption of reclaimed timber systems, regulatory changes are needed. Most critically, harmonised certification procedures across the EU would eliminate the need for case-by case structural approval, which currently adds significant time and cost to each project. Additionally, standardised protocols for non-destructive testing and quality assessment would help transform reclaimed timber from a project-specific material into a reliable construction product.
By combining careful material assessment, prefabrication, and reversible construction methods, INBUILT shows how timber reuse can become a realistic and scalable solution when the right conditions are in place.
This article was written by Natascha Steiner (KIT) and curated by Giorgio Alessandro (Greenovate! Europe) for the INBUILT project.
