Thermal breaks in wall or roof systems are typically constructed of extruded polystyrene or other similar plastic-based products to provide a separation from a conductive element within the wall system to the outside. Thermal breaks also exist in glazing framing systems enabling the inner and outer components of the frame to be thermally separated by plastic extrusion.
Are thermal breaks required in the NCC 2019 - Vol 1?
Within the NCC 2019 - Vol 1, the Deemed-to-Satisfy Provisions within Part J0 - Energy Efficiency set out the requirements for thermal breaks within J0.4 - Roof Thermal Brakes & J0.5 Wall Thermal Breaks.
These provisions set out the intent to ensure that material with an R-value of not less than R 0.2 is installed at points of contact between a metal element within a roof or wall system in order to reduce the heat loss associated with it.
Where a project is undertaking a Performance Solution, thermal breaks are not required but will be likely in the case of highly glazed or still structured buildings.
Standards used for calculating the effectiveness of a thermal break
Within the NCC 2019 – Vol 1 - Vol 1, the Deemed-to-Satisfy Provisions within J 1.2 - Thermal Construction - General set out the requirements for assessing thermal breaks and the resultant Total R-value to be in line with AS/NZ 4859.2: Thermal insulation materials for buildings - for roof and floor systems.
Intern, AS/NZ 4859.2 references the Standard NZS 4214:2006: 2006: Methods of Determining the Total Thermal Resistance of Parts of Buildings - and herein lies the requirement to access the thermal bridging impacts of structural framing and similar structural elements that would cause a repeat thermal bridge.
As a result of the above, the intent of the Standard NZS 4214:2006: 2006 aims to cover structural framing and similar structural elements and repeat thermal bridges, Specification J1.5a: Calculation of U-Value and solar admittance - intern provides the calculation requirements for wall systems which follow the same Standard for typical construction and references the Specification J 1.5b for the calculation of spandrel systems.
Are all thermal breaks combustible?
Due to this plastic content, thermal breaks are typically combustible and need to be considered against the Deemed-to-Satisfy Provisions within C1.9 - Non-combustible building elements - where it is required that all type A and B constructions are considered. New products for wall and roof systems are now on the market, allowing for non-combustible considerations of the thermal break.
In regards to high-performance, thermally broken glazing systems, thermal breaks are stated as being a non-combustible building element and do not apply to C1.9 - Non-combustible building elements.