What is 'roof runoff'?
Roof runoff is a term that refers to water that runs off from installed roofing materials. Runoff water (which usually ends up in the stormwater system) also comes from roads and other drained areas. It may contain contaminants.
Why is Auckland Council concerned about roof runoff?
Auckland Council is concerned about the level of contaminants like zinc in Auckland's harbour sediment. Auckland Council has commissioned a number of reports that have identified main sources of zinc as unpainted roofs and car tyres (which contain zinc oxide).
What is New Zealand Steel doing about the Auckland Unitary Plan Zincalume restrictions?
New Zealand Steel has made a submission in relation to the Proposed Plan seeking guidance as to whether the installation of ZINCALUME® coated steel fell within the definition of a high-contaminant generating area. Note, ZINCALUME® contains a clear coating, but it is unclear whether that coating is sufficient to exclude it from the definition.
Auckland Council has written to New Zealand Steel stating "In view of the ambiguities in the definition, and the fact that the rules and definition will be the subject of scrutiny and technical evidence during the hearing process on the Proposed Plan, the Council has taken the view that, until the Proposed Plan provisions are confirmed, ZINCALUME® roofing, spouting and external walls cladding and architectural features will not require resource consent where their area exceeds the installation thresholds in the rule".
How can zinc runoff from roofs be minimised?
The use of modern roofing materials like ZINCALUME® coated steel and COLORSTEEL® prepainted steel greatly reduces the amount of zinc or zinc compounds in runoff water. The runoff of zinc from older galvanised steel roofs can be very effectively controlled by periodic painting.
How can zinc runoff be prevented from entering waterways?
Stormwater retention and treatment facilities can prevent contaminated stormwater from entering waterways. In rural situations or township developments stormwater retention and treatment facilities can be a simple and effective preventative measure.
Does factory painting of steel prevent the runoff of zinc?
COLORSTEEL® prepainted steel minimises zinc in the roof runoff through a combination of the barrier provided by the paint system, and the superior qualities of the ZINCALUME® coated steel substrate.
Are the media reports about zinc runoff correct?
It is a fact that zinc levels in sediments of waterways are changing, however scientific studies are yet to show whether this is harmful to the environment.
While water runoff from roofing products does contribute to zinc levels in stormwater, there are many other sources. These include road runoff containing contaminants from tyres, brake pads, bitumen, road barriers and signs.
Unfortunately generalisations have been drawn by commentators that treat all steel roofing materials as 'bad', leading to incorrect conclusions.
Soil is a main contributing factor of zinc contamination. In areas of urban development and construction where soil has been disturbed, zinc levels are typically higher.
Zinc levels in runoff vary widely, depending on environmental conditions, age of roof, composition of coating etc. Zinc in stormwater exists in different forms and the nature of each of these forms and their impact on the environment is poorly understood and often misinterpreted.