Reducing pollution raises roofing price

By WAYNE THOMPSON

The cost of putting a roof over your head may be about to rise, as councils crack down on the use of unpainted metal roofing materials.

The move is calculated by the roofing industry to add about $6 a sq m to the cost of installing the popular mixed zinc-aluminium material.

It is prompted by councils' efforts to clean up heavy metal contamination in stormwater run-off.

Zinc in run-off has raised concerns for shellfish health after a study commissioned by Auckland and Waikato councils.

The Auckland Regional Council said the study showed high levels of zinc and some lead in water draining from galvanised iron roofs.

The zinc-aluminium product known as zincalume produced moderate levels of zinc, said ARC stormwater manager Roger Seyb.

A draft policy paper arising from the study had gone to councils and the roofing industry for comment.

It says councils' catchment management plans need to assess the effects of roof contaminants in urban areas.

Use of exposed metal roofing - galvanised iron, unpainted zincalume and copper - could be discouraged by requiring source control of roof contaminants in order to get resource consent.

A painted metal roof surface was an effective control to reduce contaminants in estuaries, said Mr Seyb.

Unpainted galvanised iron was widespread in older urban areas, with up to 69 per cent of roofs in suburbs such as Westmere, and the CBD, being made of the material.

Galvanised iron and zincalume were used extensively in industrial areas and these contributed to higher concentrations of zinc.

Mr Seyb said weathering of the roof gave off more contaminants.

It was suggested that for existing high-risk roofs councils should have a programme of gradual replacement and education.

They could encourage maintenance of existing exposed metal roofs by using low-zinc-content paints. Home-owners would not have to replace a roof, though they could disconnect the downpipe to let the run-off flow over the lawn for treatment.

New Zealand Steel said it was validating test results with the ARC. A company spokeswoman said there was a range of potential sources of zinc in the environment, including vehicle tyres, and motorway run-off.