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BCA 2019 Volume Two (Class 1 houses), Clause 18.104.22.168 requires that if a pliable building membrane is installed (building wall wrap) it must be a vapour permeable membrane for Climate Zones 6, 7 & 8.
In Sydney imagine a line from Berowra, Hornsby, Castle Hill, Parramatta, Milperra, Lucas Heights & Heathcote to the west of this is Climate Zone 6, wall wraps must be permeable to reduce risk of condensation occurring.
- Standard sarking is not permeable at 0.01 μg/N.s (poor)
- AS 4200.1 minimum requirement 0.14 μg/N.s (low permeability)
- James Hardie Wall Wrap 2.2 μg/N.s (very good)
- Proctor RW 4.5 μg/N.s (excellent)
James Hardie wall wrap is also a reflective barrier which suits a temperate climate like Sydney.
Proctor RW is not reflective which would be a better choice in a colder climate like Blue Mountains or Southern Highlands.