BUILDING FABRIC 33 TAKE IT TO THE BRIDGE
Simon Hill of Schöck explains the complexities around balcony design detailing to avoid thermal bridges, and why it must incorporate efficient thermal insulation
I
mproving the thermal performance of a building envelope by minimising energy usage has become increasingly
important in the drive for sustainability and energy efficiency – particularly with residential new build and renovation. Critical to this process is the avoidance
of thermal bridging. As such, designers need to be aware of how significantly thermal bridges can compromise the value of the installed insulation.
THERMAL BRIDGING A thermal bridge is a localised area of the building envelope with significantly higher thermal conductivity than surrounding areas, and typically occurs where a material with high thermal conductivity penetrates the insulation layer. Cantilevered balconies are the most
critical thermal bridges, and their presence results in a higher heat transfer through the building assembly and colder surface temperatures on the warm side of the assembly.
The main consequences will be higher energy consumption for heating, non- compliance with Building Regulations, and condensation. The latter leads not only to structural integrity problems, but the potentially serious occurrence of mould growth too.
REQUIRED STANDARDS The latest version of the Building Regulations Part L (2013, with 2016 amendments) and associated guidance document for residential construction Approved Document L1A (ADL1A) require that thermal bridging be included in the fabric heat loss calculations. The Government’s Standard Assessment Procedure (SAP 2012) is the model used to provide evidence that the carbon emissions target has been achieved. Also the SAP calculation includes the term HTB (heat loss due to thermal bridging). There are of course also voluntary certification schemes such as BREEAM and Passivhaus, however, despite this background of increasingly stringent
DESIGNERS NEED TO BE AWARE OF HOW SIGNIFICANTLY THERMAL BRIDGES CAN COMPROMISE THE VALUE OF THE INSTALLED INSULATION
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