Auckland Council Proposal Would Raise The Cost Of Building

The Proposed Auckland Unitary Plan (PAUP) contains a regulation preventing the use of uncoated roofing and cladding with an exposed surface or surface coating of “more than 10% zinc or copper”. This proposal would effectively ban the use, going forward, of metal roofing that is not coated. There is no definition of what a coating must comprise, other than not containing 10% zinc or copper.

Zincalume® steel, is the foremost product used in New Zealand and Australia for buildings not using factory painted cladding or rainwater goods.  Factory painted steel roofing is available in NZ under the COLORSTEEL® and Colorcote® brand names. Such a regulation would clearly prevent the use of any roofing, wall cladding, or rainwater goods made from galvanised steel, zinc or copper which is not coated.   As written, it is not clear whether or not Zincalume® steel would fall within the definition or the rule.

Both New Zealand Steel and New Zealand Metal Roofing Manufacturers Inc (NZMRM) have made submissions to Auckland Council on the Plan and the ambiguity around the definitions and the rule itself.  Subsequently, the Auckland Council has agreed that the proposed restriction will not take immediate effect for Zincalume®, meaning that during the interim period of the formal PAUP process (extending to at least 2016) Zincalume® will not be captured under the current definition in the PAUP and will not require Auckland-wide consent during this formal review process.  We believe that the Auckland Council  intends to engage with the industry during the PAUP finalisation process and we welcome this approach.

The restrictions proposed in the Plan would restrict the use of metal roofing that is not coated, except for pure aluminium or stainless steel. 

Scope readers will be aware of the industry’s significant advances in technology over the last 20 years, resulting in a 90% reduction in the weight of zinc per square metre on roofs so the technical discussions and arguments to be dealt with through the PAUP process are very significant.  

While houses in most cities, including the previous Auckland City, are increasingly using prepainted materials (COLORSTEEL® or Colorcote®) we estimate that 10-15% are still being clad with unpainted Zincalume®.   This may be for architectural or for cost reasons.  Typically buildings designed specifically for the appearance of unpainted cladding are larger and use it for walls as well as the roof.  Whether painted before, during or after installation in order to maintain this (zinc-tight) status, as well as for appearance, such materials will need repainting during the 50 year expected life of a building.  The frequency of the repainting will depend on the location and exposure of the roof/wall and the quality of the paint from the first repaint, but experience shows that two repaints is a minimum (currently when it is done to maintain the appearance of the cladding). 

There is no current (or proposed in the PAUP) regulation to require repainting of these prepainted roofs when the initial paint coat loses its effectiveness in limiting the concentration of zinc (or copper) in the water from a roof.  It would seem that the only way for this proposed regime to be effective in its intent would be to pass a bylaw requiring regular re-painting of these materials and to support that with certified inspections.  The criteria for such repainting are not clear.  We suggest such a by-law would be more usefully applied to existing buildings with galvanised roofs.  This of course would require more action from the Council than just controlling the use of approved materials through the consent process..

In the now very large Auckland Council area, the majority of agricultural buildings have traditionally been unpainted as appearance is unimportant, and many warehouses, commercial buildings and factories have also been unpainted; all of these would be affected by the proposed regulation.

There are also a very large number (far more than will be built in the next ten years) of existing houses up to 100 years old, all with galvanised roofs in various stages of decline.

In 2005-7 the ARC proposed a similar ban, but research by the NZMRM, New Zealand  Steel and Tonkin and Taylor, and some other technical investigations showed this to be ecologically unnecessary and the ARC report was withdrawn, leaving Zincalume® (unpainted) as an acceptable material, but not any other roofing material with an exposed surface containing a greater proportion of zinc (i.e. no galvanised).  

The NZMRM has objected to this regulation on two grounds – 

  • Technical; as no explanation is provided for the correlation of stormwater objectives and the limit of 10% zinc;
  • Economic; while the cost 

implications of using prepainted are provided (as required by the RMA S32) this is only shown per house, and excludes any repainting cost or the likely overall cost to the economy.  It does say “Greater emphasis on on-site stormwater requirements will have consequential costs to site owners and developers and lead to a shift in cost from the public to private sector.”  “On-site controls will require on-going maintenance and compliance which will result in on-going costs for site owners and the requirement for compliance management regimes.”  Although these comments apply to the stormwater retention and treatment proposals they would apply to the painting requirement (if there was one introduced).

In summary, the NZMRM believe there is no technical justification for this philosophical/ecological position of which the cost will fall entirely onto building owners.  This cost could be very large, and if extended throughout NZ as a result, the overall cost to the economy could be extreme.   This comes at a time when central Government is seriously trying to reduce the cost of building in NZ, not increase it.  

The salient points of NZMRM’s objections to this proposal are:–

  • the ambiguity in the definitions and the rule itself; This is an unnecessary means of reducing zinc in stormwater without proper assessment of cost, except that it will be borne by the “private sector”;
  • It has a history of previously being rejected by the ARC after representation by industry;
  • There is no technical basis provided supporting the limit proposed for zinc in roofs in relation to the target concentration of zinc in rainwater run-off of 30 µg/L;
  • There is no defined basis for the target level of 30µg/L nor consideration of the cumulative effects of rainfall events from roofs and the combinations of other rainfall run-off from other materials and surfaces which significantly reduces any impact from roofs;
  • The total cost to building owners and so the economy over the  50 years for which we expect buildings to last will be very high,;
  • The industry has already made significant advances in technology over the last 20 years resulting in a 90% effective reduction in Zinc run-off on unpainted roofs in NZ via:
  • 150g/m² aluminium/zinc coated steel verses Z450g/m² zinc (1994 introduction of Zincalume®) – an 85% reduction in the weight of zinc per sq metre on roofs; and
  •  Increase in the expected life of the roof of 30% providing a net run-off effect reduction of 90%. 

We consider this proposal is actually quite hard to pick up, so where is it to be found? 

It is buried several layers deep in the PAUP and is summarised below:

Part 3 Section H 4.14 - Stormwater

3.1 – 3.2.1, and 3.2.2 refer to run-off areas that need to be controlled when run-off is from an HCGA  (high contaminant generating activity) which includes high contaminant yielding roofing under Section 9(2) of the RMA. provides the roof areas that need to be controlled 

  • “2. New high contaminant-yielding roofing, spouting, cladding or architectural features
  • a. The total area of high contaminant yielding roofing, spouting, cladding or architectural features used on the site must not exceed: 
  • i. 25m2 in urban areas 
  • ii. 25m2 in any rural zone where the stormwater runoff from the roofing, spouting, cladding or architectural features is piped directly to a watercourse 
  • iii. 250m² in any rural zone where the stormwater runoff from the roofing, spouting, cladding or architectural features is directed to any vegetated drain/swale, wetland or similar.”

Tables 3 and 4 in 3.4.2 show the control limit of 30 ppb (µ gms/l) for 95% of runoff. In Section 4 Definitions – H - is the definition of HCGA 

“High contaminant-generating areas. Specific areas that contribute a high proportion of contaminants to the overall site stormwater discharge. High use roads are also areas that generate high contaminant loads and are defined elsewhere. Includes:

  • high contaminant yielding building roofing, spouting, and external walls cladding and architectural features using materials with an:
  • exposed surface or surface coating of metallic zinc or any alloy containing more than 10 per cent zinc
  • exposed surface or surface coating of metallic copper or any alloy containing more than 10 per cent copper or
  • exposed treated timber surface or any roof material with a copper or zinc containing algaecide”

This covers unpainted galvanised steel   (or any uncoated metal roof or wall except aluminium or stainless steel); copper spouting, flashings, and asphalt shingles (which often contain copper as an algaecide), or any exposed “treated” timber. As written, it is not clear whether products such as Zincalume® would fall under the proposed rules. 

We are unable to find any basis for where the 10% zinc comes from or how it links to 30 ppb.

The definitions of HCGA in this area come from Technical Report 2013/035 although a link to this is not provided in the PAUP itself.

This 125 page report does not appear to explain how 10% is derived, or suggest where it comes from.  As Zincalume® is 20% zinc by volume; it would specifically prevent the use of Zincalume® (depending on how the term “coating is defined)– which is the predominant unpainted roof cladding material for residential, agricultural and industrial buildings in New Zealand.

Section 32 of the RMA (extract) –s32 

Requirements for preparing and publishing evaluation reports

(2) An assessment under subsection (1)(b)(ii) must—

(a) identify and assess the benefits and costs of the environmental, economic, social, and cultural effects that are anticipated from the implementation of the provisions, including the opportunities for—

(i) economic growth that are anticipated to be provided or reduced; and

(ii) employment that are anticipated to be provided or reduced; and

(b) if practicable, quantify the benefits and costs referred to in paragraph (a); ……….”

The only reference to this in the PAUP is in:

S 32 Evaluation for Report 2.2.4 of the PAUP p 31.

“The main costs expected from the proposed policies and rules are: 

Greater emphasis on on-site stormwater requirements will have consequential costs to site owners and developers and lead to a shift in cost from the public to private sector.  

On-site controls will require on-going maintenance and compliance which will result in on-going costs for site owners and the requirement for compliance management regimes.”

This suggests the significant costs associated with the proposal are intended to be borne by the building owner.  We believe these costs to be very large, and that they have not been adequately identified as required by the RMA. S32

Auckland City Technical report 2013/043 deals in great detail with the (large) costs of stormwater retention and treatment, but has only this to say about the cost of roof cladding

“2.9.4  Roofing Materials 

As mentioned in Section 1, HCGA areas also include uncoated galvanised iron (sic) and copper/zinc based cladding materials.  In these cases the least expensive option is to use appropriate non copper/zinc generating materials.  For roofing, this would be appropriately coated aluminium (sic) roofing materials. 

For example, the supply cost of coated aluminium cladding is approximately $21/m2 compared to uncoated at $15/m2, an additional cost of $6/m2 (Source: Roofing Supplier).  Installation and maintenance costs are assumed to be the same, giving the same extra total present costs of $6/m2

For a house with a 200m2 roof, this equates to an additional $1,200.”

MRM notes 

  • We agree with the cost of $6/m² for pre-painting, but comment, as the report does not, that this is a 40% increase in cost – not trivial.
  • Maintenance cost in fact is significantly higher as repainting in situ is much more expensive than the original pre-painting.

An audit of the report was carried out by NZIER/Harrison Grierson and it says, inter alia, 

“It is common in the sampled topic reports to include an assertion that the information is sufficient and then not justify or support the statement.

There is very little back-up for these assertions (e.g. by referring to references or appendices).   

There is very little in many sampled topic reports on the uncertainties and limitations of the options presented. “

In this case it seems (but is never stated as such) that the only alternatives are the use of painted zinc-or copper- containing roof and wall cladding etc., or retention of stormwater and treatment in some way to remove dissolved zinc. This method (of zinc removal) is not mentioned and we think it may not be possible in any economically practical means for on-site solutions.

This audit comment supports the NZMRM view

The NZMRM says that the significant reduction in zinc resulting from the change to Zincalume® and its painted variants has been produced by the industry and recommends that the Auckland Council leaves new roofs to the industry and that they undertake a review of the need to achieve these low levels of zinc from roofs.  Key factors the Auckland Council needs to consider:

1.The target levels of zinc from roofs are not substantiated;

2.The derivation of the target levels for roofs after consideration of the cumulative effects of all runoff have not been addressed;

3.The consequential determination of 10% zinc content in coating material has not been provided;

4. Coating has not been defined;

5.The ability to install economically viable treatment systems is doubtful

6.The apparent omission of consideration of treating existing HCGAs as being a more effective target – e.g. car tyres;

7.The assumption that painted cladding is acceptable and then ignoring the need to implement controls and painting at a significant cost to Auckland home owners cannot be ignored;

8.The industry has reduced the amount of zinc in stormwater from unpainted roofs by 90% over the last 20 years with a cost saving to the building owner; and

9.The industry is continuing to improve technology and is currently reducing the amount of zinc in the coating of mild steel by another 20% with an additional lifespan of the material. 

New roof construction should be left to industry and if the Auckland Council is serious about reducing zinc levels in stormwater there are other areas contributing far more that can be easily addressed.

The industry is achieving greater results for the environment at REDUCED COST to the country than could ever be attempted by restrictive material use regulation.  

Criticism of a proposed regulation or standard should always be accompanied by a recommended change to improve it. 

So, consider this 

This article contains a number of pictures of roofs made of metallic coated steel, in size from small to large, and condition from very old to new.  What they are made of is labelled.


a) Galvanised steel for roofing was phased out in 1993;

b) Zinc (galvanised) coating was originally 200-300 gms/m² on the topside; Zincalume® coating is 75 gms/m² on the topside of which 45% by weight is zinc (20% by volume);

c) Zinc (galvanising) protects the underlying steel from corrosion by continuous sacrificial protection, which is why it has a finite life to red rust; and

d) Aluminium/zinc (Zincalume®) protects the underlying steel by forming an inert film of aluminium oxide over the entire surface which will last indefinitely unless it is seriously damaged or interrupted (at edges or holes or scratches) – when the zinc component acts as protection. 

Even assuming  

i) There really is an increasing (rather than declining) problem with bio-active zinc compounds in Auckland’s harbours causing harm to marine organisms; and

ii) This bio-active zinc can actually be derived from metallic zinc on roofs (rather than e.g. zinc oxide from vehicle tyres), (neither of which assumptions have been demonstrated or proved), and 

iii) When old galvanised roofs (all now at least 20 years old) finally die or are determined to be unattractive, they will be replaced with Zincalume® painted or unpainted;


Which of the roofs illustrated would you think poses a greater environmental risk, now or in the near future?  

Would it not be much better to repaint or replace the older galvanised roofs, rather than potentially banning unpainted Zincalume®?  Or is it just too difficult?  

Between now and the final implementation of the PAUP in 2016-7 there will be opportunities to view the progress of the Plan and to make some comment. 

This will start soon when submissions to the PAUP will be published between May and July.  

We suggest that involvement by Scope readers can influence the outcomes, and ask you to make yourselves conversant with this aspect of the Plan as well as any other issues that may affect you.