Reflective foils or surfaces and their effectiveness in emitting or reflecting energy as thermal radiation are measured by an emissivity, expressed as a ratio between 0 to 1.
Where a product has a stated value, these are typically tested against either AS/NZS 4200.1:2017: Pliable building membranes and underlays or ASTM E408 - 13(2019): Standard Test Methods for Total Normal Emittance of Surfaces Using Inspection-Meter Technique.
In the case of the building envelope, Speckel uses the prescriptive calculation methodology within AS/NZ 4859.2: Thermal insulation materials for buildings - for determining the thermal resistance of airspaces with parallel bounding surfaces of varying emissivities through stated tested values only.
The steps below will allow you to review the emissivity of varying products when you build a Wall System to the requirements of J 1.5 – Total System R-value for walls (AS/NZS 4859.2:2018) requirements, including thermal bridging (NZS 4214:2006).
Step 1 – Let’s first reuse the Lightweight Cladding (Cavity fixed to 92mm steel frame) Wall System we created in Wall Systems Tutorial 1 – Getting Started.
Step 2 – Under the Water Control Layer, select a generic Class 1 - Single-sided Reflective Vapour Barrier.
Step 3 – Next up… let's adjust the direction the Class 1 - Single-sided Reflective Vapour Barrier is facing to see the resulting difference in Total R-value.
Step 4 - When your happy, and always check for condensation risk when using Class 1 - Single-sided Reflective Vapour Barrier, simply click Performance Solution and download your Report.