What is thermal bridging?
A thermal bridge, also called a cold bridge or heat bridge, is an area of a building (usually the envelope) which has a significantly higher heat transfer than the surrounding materials, resulting in an overall reduction in thermal insulation of the building.
Thermal or cold bridges occur where the insulation layer is penetrated by a material with a relatively high thermal conductivity. Balconies provide an attractive and practical architectural feature, however, because connection points pass through the building envelope, if the fixing detail is not thermally insulated it can create a thermal bridge from the cold balcony to the warm inside. This causes condensation to form at cold points inside the building, increasing the potential for mould.
Key Points of Thermal Breaks
- See Part L section 1a
- See BRE Information Paper IP/06 106
- Thermal performance must consider the entire buildings.
- Ensure all components with a thermal role work synergistically
- Get a balance between thermal and structural performance
What is a thermal break?
A thermal break is a material with low thermal conductivity, placed in an assembly, to reduce or prevent the flow of thermal energy between the inside and outside of a building.
Do I require a thermal break?
The choice of balcony connector is not only fundamental to structural integrity but also ensures the balcony is thermally isolated.
The thermal performance of the building envelope is a key design consideration in meeting today’s stringent energy efficiency standards. A thermal break must be specified to reduce heat loss and the risk of condensation.
Minimising the effect of cold bridging on a building’s overall thermal performance, by way of reducing heat loss, is required to comply with Building Regulations (e.g. Part L), NHBC, BRE and other requirements. Useful guidance on this is available in BRE Information Paper IP/06 106: ‘Assessing the effects of thermal bridging at junctions and around openings’.
Part L (Conservation of Fuel Power)
Part L has become more stringent over the years as it aims to reduce heat loss and avoid the issues of condensation and material corrosion/degradation.
Part L section 1a in the building regulations states that: ‘reasonable provision shall be made for the conservation of fuel and power in buildings, by limiting heat gains and losses through thermal elements and other parts of the building fabric”.
Citation 4 (50a/51) clarifies that the building fabric should be constructed ‘so that the Insulation is reasonably continuous over the whole building envelope, and constructed so that there are no reasonably avoidable thermal bridges”.
Part L states that whilst the use of non-accredited products is acceptable, these should be proven to comply with BRE IP1 06 as part of required Part L building assessment. This requires thermal bridging to be less than the default value for accredited details (inc. products certification by UKAS accredited organisations).
BRE (Building Research Establishment)
BRE is an organisation which gives guidance aiming to support compliance with building regulations. BRE have established BREEAM (BRE Environmental Assessment Method) which has become a leading and widely used environmental assessment method for buildings and sets standards for best practice.
Whilst BRE best practice guidance is not mandatory legislation, working to these standards makes Building Regulation compliance easier. Coupled with this, many schemes embrace BREEAM for which high ratings can only be achieved through embracing BRE advice. In particular, with thermal performance of balconies compliance to Part L, guidance can be found in the BRE document IP1 06 (Assessing the effects of thermal bridging).
Two key parts with regards to thermal breaks can be found in Section 4.2 of IP1 06, which recommends critical temperature factors for avoiding mould growth in residential buildings as 0.75 fCRsi and section 5 of IP1 06 which provides a thermal performance calculation. Section 5 also states that when insulation is penetrated by a highly conductive element, for example a steel girder penetrating the insulation layer, the constructional thermal bridges should have its own point thermal transmittance calculated’. This includes balcony connections.