As of 1 May 2009 the Building Code of Australia requires all calculation reports for demonstrating the performance of insulation products to be carried out according to the 2006 amendment of AS/NZS 4859.1:2002. This means any product labeling and promotional materials showing calculated system R-values should be updated to meet the changes in the 2006 amendment.
See the Australian Building Codes Board for more information.
The amendment includes adjustments to a product’s tested emissivity, in Section K3.2. These adjustments are summarised as follows:
-For vertical and downward facing surfaces, emissivity of 0.03 or as tested, whichever is greater
-For upward facing surfaces in non-vented cavities where the cavity is fully sealed, emissivity of 0.03 or as tested, whichever is greater
-For upward facing surfaces in non-vented cavities where no special precautions for the prevention of air ingress have been included, assume slight dust cover and add 0.05 to the tested emissivity
-For upward facing surfaces in naturally ventilated space, assume moderate dust cover and add 0.25 to the tested emissivity.
Section K4.2 of the amendment addresses the ventilation of roofs, walls and floors. The implication of this section is that tile roofs are assumed to be naturally ventilated; whereas metal roofs are assumed to be non-vented. This means that any reflective foil insulation installed directly under a tiled roof will be penalised with an additional 0.25 added to the tested emissivity for moderate dust cover.
Section 3.12.1 in volume two of the Building Code of Australia gives the requirements for building thermal insulation. Table 188.8.131.52 gives the minimum total R-Value for different climate zones, with the minimum being 2.7 downwards for zone 1 and the maximum 4.8 upwards for zone 8.
The effect of the amendment will mean that some systems, particularly tiled roofs with the insulation installed parallel to a roof, and including an anti-glare upper surface, and without any sarking, will not achieve an R-Value of 2.7.
One solution to this problem is to use reflective foil and bubble cell insulations in new installations in a similar manner to the retrofit case. This would mean specifying systems for new installations with a reflective sarking (with an upward facing anti-glare surface and a downward facing low emissivity silver surface) under tile roofs, (metal roofs may not need the sarking) and install reflective insulation parallel to the ceiling with both upper and lower surfaces being low emissivity silver.