Technical Booklet E Fire Safety·Page 138·5.5(e)
Thermal breaks guidance
Thermal breaks are small elements restricting thermal bridging with no minimum fire performance required, but must not span compartments and should be limited to the minimum size necessary.
thermal breaks are small elements used as part of the external wall construction to restrict thermal bridging. There is no minimum performance for these materials. However, they should not span two compartments and should be limited in size to the minimum required to restrict the thermal bridging (the principal insulation layer is not to be regarded as a thermal break);
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