Bio-attributed polyurethane insulation for lightweight commercial roof renovation

Improving the energy performance of existing buildings has become a complex balancing act. Especially in commercial properties, higher energy efficiency targets, lower CO₂ emissions and additional uses such as photovoltaic systems often meet roof structures that were never designed for these requirements.

Lightweight, high-performance insulation is critical when commercial roofs reach their structural load limits — particularly when photovoltaic installations are planned.

This was precisely the situation at a DIY store in Bonn. The roof areas were to be refurbished to modern energy standards and prepared for PV installation – despite the fact that the existing load reserves were almost completely exhausted. The project team therefore faced the challenge of reconciling technical feasibility, sustainability, and economic viability.

How can a commercial roof be renovated at its structural load limit?

Marco Prediger (Wierig GmbH) describes the starting point clearly:
From the outset, the project was conceived as an energy renovation with a strong sustainability focus. However, once the existing drawings were reviewed and roof samples were taken, it became evident that the available load reserves were fully utilized when accounting for insulation, waterproofing, and the planned photovoltaic system.

A key constraint was the pumice slab ceiling acting as the load-bearing structure. Mechanical fastening was not an option for structural reasons. As a result, any viable solution had to combine very low weight insulation with a fully bonded roof build-up.

Choosing materials under tight constraints: Why PU insulation became a key enabler

For this reason, the more sustainable LINITHERM LOOP polyurethane insulation boards were selected. For Marco Prediger, several factors were decisive alongside the CO₂ footprint reduction:  excellent thermal performance, low weight and the ability to realize the roof build-up without additional mechanical fixings.

Equally important were practical considerations typical of refurbishment projects: system versatility, approved processing options, and reliable technical support from the manufacturer. Cost efficiency and material availability also played a role – not as primary drivers, but as necessary conditions for smooth project execution.

In projects with limited structural capacity, Prediger emphasizes the importance of flexibility. Compatibility with third-party products and the ability to implement different detailing solutions provided the required planning and execution certainty.

Sustainability without compromising performance: bio-attributed¹ PU raw materials as part of the solution

Ralf Scheffler (Linzmeier Bauelemente GmbH) highlights another decisive aspect of the material choice in the Bonn project: sustainability across the value chain under strict structural constraints.

The LINITHERM LOOP insulation systems used in Bonn incorporate more sustainable polyurethane raw materials, including the MDI Desmodur® CQ from Covestro, which partially replaces fossil-based feedstocks. These raw materials originate from renewable sources and are integrated directly into the product formulation.

For customers and building owners, this meant achieving a measurable reduction in the roof system’s CO₂ footprint without adding weight or compromising performance. Thermal efficiency, stability and durability remained fully intact — enabling the planned energy renovation and PV installation within the existing load limits. According to Scheffler, sustainability in this project was not an abstract goal, but a practical requirement achieved through material innovation, without sacrificing quality or ease of processing.

On-site execution: When details make the difference

During installation, the material choice proved its value in practice. According to Marco Prediger, the PU insulation boards were easy to handle on site. The smaller board formats allowed complex detailing to be executed cleanly and efficiently, avoiding thermal bridges.

For Prediger, the decisive confirmation came during construction rather than at the planning stage. Especially when implementing demanding details, the product quality became evident. In the subsequent project review with planners, the client and the site team, there was a shared consensus that the chosen solution had been the right one – both technically and conceptually.

Market acceptance and future outlook: How sustainable insulation solutions are gaining traction

From a market perspective, Ralf Scheffler observes a clear trend. Installers, planners, and architects are increasingly required to specify sustainable materials while relying on solutions that are proven and reliable in practice. This is precisely where PU-based insulation systems with an improved environmental profile are gaining attention.

Planners, in particular, value the improved ecological assessment, while installers highlight the straightforward handling and consistently high product quality. Today, sustainable alternatives must above all integrate seamlessly into established planning and construction processes.

Looking ahead, Scheffler sees the future of sustainable insulation in materials that deliver across the entire lifecycle – from raw material sourcing through use to recyclability. This development is driven by stricter regulations, rising energy efficiency requirements, and growing awareness of climate protection within the building sector.

Conclusion

The Bonn project demonstrates how technical performance, structural feasibility, and sustainability can be successfully combined in refurbishment projects. The decisive factor was not a single innovation, but the interaction of appropriate material selection, close collaboration along the value chain and practical, on-site execution.

1 bio-attributed insulation according to the mass balance approach