With regulations for energy efficiency, fire safety and sustainability tightening, building designers need an accurate and reliable way to model thermal performance.
Nowhere is this more important than in rainscreen façades, where structural complexity and widespread thermal bridging present unique challenges. That’s why 3D U-value calculations are emerging as the benchmark for accurate thermal modelling in rainscreen façades.
Why thermal modelling needs to evolve
U-values measure how much heat is lost through a building element and are an essential tool for architects, enabling them to design comfortable, thermally efficient buildings that comply with Building Regulations, specifically Approved Document L: Conservation of fuel and power. Simplified U-value calculations are suitable for simple build-ups such as a cavity wall, but they will fall short if applied to a rainscreen façade design.
The primary challenge in a rainscreen façade is that the build-up is far more complex. The metal fixings, brackets and other penetrations that break the continuity of the insulation create repeating thermal bridges that have complex shapes and features. A simplified U-value calculation will either apply a blanket correction factor for thermal bridging or use a simple formula to account for the cladding’s supporting rail and bracket assembly. But these approaches could be inaccurate without detailed thermal modelling of the designed build-up.
This inaccuracy at the design stage could lead to an incorrect insulation specification, which presents two risks for building designers: a compliance risk and a cost risk.
If the design looks compliant on paper, but the insulation specified proves to be inadequate, this could cause serious headaches. In buildings over 11m tall, this might cause compliance failure with the Building Safety Act’s three ‘gateways’, as well as failure to comply with Part L. And it will have an impact on building occupants, who will face higher energy bills, increased operational carbon emissions and decreased comfort.
Conversely, if the insulation is over-specified, this can have an impact on the cost of the project and its embodied carbon. It may also impact other areas of the building’s performance and design. Getting U-value calculations right from the start will help architects ensure compliance by delivering a design more likely to perform as intended in the real world.
The 3D advantage
3D U-value calculations model the actual geometry and material properties of the repeating brackets and fixings. This level of detail provides a far more accurate representation of how heat flows through the construction.
By quantifying these heat loss pathways more precisely, 3D modelling allows specifiers to balance performance and cost more effectively. It reduces the reliance on excessive insulation ‘just in case’ and helps avoid the risk of compliance failure. The data generated can also be used to refine the design early in the process, providing better performance outcomes.
Moreover, detailed thermal models with clear, structured reporting help maintain transparency across the supply chain. With increasing pressure on specifiers to demonstrate due diligence and deliver ‘real performance’, this kind of evidence is invaluable.
Why it matters now
Recent years have seen sweeping changes in construction regulation. Updates to Approved Documents L and B, the phased implementation of the Building Safety Act, and the anticipated Future Homes and Buildings Standard are collectively raising the bar for insulation performance, fire safety, and accountability.
At the same time, third-party stakeholders—local authorities, insurers, planning officers—are adopting more stringent expectations. It’s increasingly common for project teams to require non-combustible materials across all residential schemes, regardless of height, and to demand performance evidence that goes beyond what’s required by regulation.
The drive toward lower carbon buildings has also brought embodied carbon – the total greenhouse gas emissions generated to produce a built asset – into sharper focus. Specifiers are looking for solutions that balance thermal efficiency with reduced environmental impact. In this context, getting the specification right first time is essential—and that starts with accurate modelling.
From design intent to real-world performance
Buildings are now expected not only to meet requirements on paper but to perform as predicted in operation. This shift reflects a growing awareness of the ‘performance gap’—the discrepancy between expected and actual building performance. 3D U-value calculations are part of a holistic approach to closing the performance gap.
Another major contributor to this gap is installation quality. Some insulation materials, like rigid foam boards, may offer low lambda values on paper but are difficult to install correctly. Even small air gaps can drastically reduce thermal performance. Mineral wool, by contrast, is flexible and forgiving. It adapts to minor imperfections in the substrate and ‘knits’ together at joints, helping to maintain a continuous thermal layer.
When accurate thermal modelling is combined with buildable materials, the likelihood of achieving the designed performance increases significantly.
Futureproofing façades
With buildings under more scrutiny than ever, specifiers must futureproof their designs. This means choosing insulation solutions that not only perform and are non-combustible but are backed by verifiable data and designed for buildability.
3D U-value modelling is a crucial part of this process. It enables the design of façades that meet expectations and deliver consistent thermal performance, supporting compliance, and helping projects stay on budget.