6. Reflective Foil Insulation

Install reflective foil over the rafters.

All tiled roofs in energy zones 1, 2, 4, 6, and 7 shall have a tile underlay or radiant barrier and installed in accordance with the manufacturers installation specifications.

The thermal resistance of a reflective material (see Table 5) or assembly shall be expressed as system
R-value (Rsys), and shall be the combined thermal resistance, which includes adjacent air spaces.

Note: The R-value of reflective insulation is affected by the airspace between a reflective side of the reflective insulation and the building lining or cladding. The thermal performance of reflective insulation is influenced by dust and could be adversely affected.

R-values considered to be achieved by Reflective Foil Laminates
Emissivity of added reflective insulation Direction of heat flow R-value added by reflective insulation
Pitched roof (≥10º) with horizontal ceiling Flat Skillion or pitched roof (≤10º)

with horizontal ceiling

Pitched roof with cathedral ceilings º
Natural ventilated roof space Non-ventilated roof space 22º 30º 45º
0.2 outer

0.05 inner

Downwards 1.21 1.12 1.28 0.96 0.86 0.66
0.2 outer

0.05 inner

Upwards 0.59 0.75 0.68 0.72 0.74 0.77
0.9 outer

0.05 inner

Downwards 1.01 0.92 1.06 0.74 0.64 0.44
0.9 outer

0.05 inner

Upwards 0.40 0.55 0.49 0.51 0.52 0.53
Notes: (1) The above table is applicable where an air space between the external roof cladding and a ceiling assembly is divided by the positioning of a reflective foil to create two air gaps. Reflective foil insulation values include a minimum 15mm air gap on either side. Reflective insulation should work in conjunction with an air gap to be effective.

(2)The reflective surface with the lowest emissivity should preferably be facing downwards.

(3) 0.2 outer value is used where the roof is sealed, and no dust can accumulate. 0.9 outer value is used where dust can impair performance. Bright metal surfaces can generally be taken as 0.05 emissivity.