A significant amount of roofing defects we see are not installation problems. They are design problems that nobody identified before construction began.
By the time the roofer arrives, the non-compliance is already built into the plans.
The two most common design failures we are seeing are:
Both are clear non-compliances with the NCC and Australian Standards.
Under NCC 2022 Volume 2 Part H2D, AS 1562.1, and HB 39, valley gutters are not permitted on very low roof pitches. For metal roofing systems, valleys generally require minimum roof pitches of around 12° (manufacturer dependent but consistent across industry guidance).
We are regularly seeing valleys drawn on 3–5° roof pitches. This can cause water to pond, trap debris, accelerate corrosion, overflow during heavy rain, and ultimately lead to water ingress into the structure. This is a design non-compliance, not a workmanship issue.
We are also seeing roof planes discharging into parapets, box gutters without compliant overflow or a direction change, or locations where water has no compliant discharge path. This breaches NCC H2D2 and H2D6 and AS/NZS 3500.3, which require roof drainage systems to remove water without causing damage to the building.
Before construction starts, builders should check:
If this is not checked at design stage, the builder inherits the liability.
If you have any questions or need further guidance, please don’t hesitate to contact our Advisory team:
📞 (02) 6175 5900
📧 workplace@mba.org.au
