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  • PublisherCIBSE
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  • Number of pages0
  • Publication DateSep 2011
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Crossing Over: Thermal Bridges and the Design of the Building Fabric

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Crossing Over: Thermal Bridges and the Design of the Building Fabric

CIBSE Technical Symposium, De Montfort University, Leicester UK
6th and 7th September 2011

From a services engineering perspective, this research examines the importance of building fabric design and detailing with a particular focus on thermal bridging and hygrothermal performance in the fabric. Thermal bridging can account for a significant portion of overall fabric heat loss – particularly in high performing buildings. In addition to affecting overall heat load, thermally bridged components create local cold spots on interior surfaces which may damage finishes if not compensated for in the heating layout. Moisture accumulation in building fabric can compromise thermal performance, resulting in significant discrepancies from design U-values.

Understanding these concepts is increasingly important in highly insulated buildings. Thermal bridging and heating loads associated with moisture are more likely to lead to undersized heating systems where boiler sizing is optimised based on low U-values.

Using a case study and examples, this study analyses architectural detailing and fabric design to highlight the often ignored associated heating loads. It examines the internal surface temperatures of thermally bridged details and discusses the additional design requirements they impose. Finally, the impact of building fabric moisture levels on the heating load is analysed.

The purpose of this study is to highlight these very important building fabric issues as they affect building services. Services engineers need to engage architects to discuss actual performance of building fabric beyond idealised, steady-state U-values. This understanding and discussion is crucial for avoiding client call-backs related to undersized heating systems, surface condensation, and increased energy use in highly insulated buildings – particularly as regulations are pushing these buildings into the mainstream.