The NCC 2019 – Vol 1 defines R-values in various sections of Section J To assess the ability of a product or a collection of products to resist thermal transfer.
In terms of an Individual product, such as insulation, it's overall thickness is multiplied by its thermal conductivity or k-value to result in its specific R-value. This is defined within Schedule 3 - Definitions of the NCC, as follows:
- R-Value (m2.K/W) means the thermal resistance of a component calculated by dividing its thickness by its thermal conductivity.
Continuing with the example of insulation, which is the primary means by which wall systems or roof systems achieve their overall thermal performance, the NCC 2019 mandates new requirements for the testing of all insulation products as per AS/NZS 4859.1: 2018 - Materials for the thermal insulation of buildings.
The recent update to AS/NZS4859.1:2018 standard has seen changes introduced to the way the product is tested and how thermal performance (R-value) is calculated and declared, affecting bulk, reflective foil and rigid foam insulation. The biggest changes within the amended Standard relate to the thermal testing, and formal declarations of performance labelling mandated by the NCC as the most recent Standard must always be adopted.
What's the value of individual products are understood they can then be collated together to provide a total r-value which must include all building material insulation materials as the face is thermal bridging and associated surface resistances. This is also defined within schedule 3 – Definitions of the NCC as follows:
- Total R-Value (m².K/W), for the purposes of Volume One, means the sum of the R-Values of the individual component layers in a composite element including any building material, insulating material, airspace, thermal bridging and associated surface resistances
When undertaking taking a calculation assessment of the total r-value against NCC requirements, the AS/NSZ 4859.2: 2018 - Thermal insulation materials for buildings Is used and is a primary reference within Part J1 - Building Fabric.