Emittance
Emittance measures how readily a surface radiates heat. In insulation, a surface emittance of 0.05 or less qualifies as reflective under NCC 2022 and AS/NZS 4859.1.
Ask Chalkline about this →Emittance measures how readily a surface radiates infrared heat energy, expressed as a number between 0 and 1. A surface with emittance of 0 radiates no heat at all; a surface with emittance of 1 radiates the maximum possible. Polished aluminium foil typically sits at 0.03 to 0.05 (low emittance, high reflectivity); painted metal, plasterboard, and timber sit at 0.85 to 0.95 (high emittance, low reflectivity).
In Australian building insulation, emittance determines whether a surface qualifies as “reflective” under NCC 2022 Housing Provisions Part 13.2 and AS/NZS 4859.1:2018. A reflective surface must have emittance of 0.05 or less when facing an enclosed airspace. Where the surface faces the sun during construction (requiring an anti-glare coating for WHS), the limit rises to 0.10 (verified 2026-05-10, NCC 2022 Housing Provisions Part 13.2, ABCB).
Dust accumulation raises emittance over time: roof-space foil can move from 0.03 to 0.2 or higher after years of dust settling, degrading the reflective R-value contribution. This is a known long-term performance risk with reflective insulation in roof spaces.
Also known as: emissivity (same concept; “emittance” is the preferred term in Australian building standards).
Category: Insulation and energy efficiency
Related
- Bulk vs reflective insulation: the article where emittance thresholds are most relevant
- R-value: the thermal resistance measure that emittance affects
- Sarking: the reflective membrane layer where emittance is a key spec
See also
Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.