BUILDING FABRIC 57
A THERMAL BRIDGE TOO FAR?
Following changes to Part L in 2021, carbon emissions in new builds have to be signifi cantly lowered. Simon Hill of Schöck says specifi ers need to be aware how greatly thermal bridges can aff ect insulation values
Hendon Waterside
localised area of the building envelope with signifi cantly higher thermal conductivity than surrounding areas is known as a thermal bridge. Typically occurring where a material with high thermal conductivity penetrates the insulation layer. antilevered balconies are critical examples, resulting in higher heat transfer through the building assembly and colder surface temperatures on the warm side. The main consequences will be non-compliance with Building egulations, higher energy consumption for heating, condensation and the formation of mould growth. The 2021 edition of Part L (which replaces L1A 2013) sets out the minimum thermal requirements for avoiding such issues. Thermal bridging must now be included in fabric heat loss calculations and the Standard Assessment Procedure calculation (now updated to SAP 10.2) includes the term HTB (heat loss due to thermal bridging). A further
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concealed by subsequent work, an audit should be undertaken to confi rm the designed details have been constructed. hotographs should be taken to verify that the products used are those shown in the original design. If there are substitutions, the revised specifi cation should be re ected in the SA calculation and report in the Building Regulations England Part L compliance report (BREL report). This information needs to be signed off by the SAP assessor.
General tightening of U-values – requiring greater insulation requirements and the construction of better performing thermal break details – are also included in the revised art . Additionally, it encourages HTB assessment to be carried out through thermal calculation for a more realistic evaluation of existing thermal junctions. The default Y-value has been increased to 0.20 W/m2
change involves an onsite audit for new dwellings. It is now required that before different construction junctions are
update to discourage generic estimations – as this does not reveal the performance of thermal break junctions, including
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