42


feature


roofing, cladding, insulation & structural systems


closing the thermal performance gap with 3D U-value calculations


   Knauf Insulation


Why thermal modelling needs to evolve U-values 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 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. 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.


Continued on page 44... 


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