NZ Metal Roofing Manufacturers, Sustainability, and the NZ Green Building Council Rating Tools

People have been talking about “sustainability” for a long time without really defining what is sustainable other than something that can continue. In 1987, the General Assembly of the United Nations set up the World Commission on Environment and Development, with the objective of proposing long-term environmental strategies for achieving sustainable development by the year 2000 and beyond. They generated a huge report of which a key message was the definition of sustainable development by the Chair, Gro Harlem Brundtland, as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”.  There have been other definitions, but probably nothing better.
Buildings are serious consumers of materials and energy and generators of waste and pollution and so need serious mitigation of these factors in order to comply in any way with the definition of “sustainable development”.

Following shortly after the WCED report the Building Research Establishment (BRE) in the UK developed methods of measuring and controlling the environmental effects of buildings and created the programme called BREEAM (Building Research Establishment Environmental Assessment Method), first published in 1990. This is the world’s longest established method of assessing, rating, and certifying the sustainability of buildings, and is used in a number of countries worldwide.

Other countries have developed their own programmes and in 2003 the Green Building Council of Australia (GBCA) was created and set up its own programme, a building certification scheme called “Green Star”. Shortly after, New Zealand set up the NZ Green Building Council (NZGBC) which adopted the Green Star programme more or less completely from Australia. South Africa also adopted the programme. Subsequently NZGBC has also developed the Homestar programme for residential buildings. 

Green Star
The Green Star rating tool is a method of assessing the sustainability of a building in terms of (in short) what it is made of, what goes into and out of it, and the effect of its use on the environment. Clearly what the building is made of is a one-off “cost” which effectively declines per annum over its life, while the effects of its use, however mitigated during its life, accumulate over this life. Green Star (as do other schemes) emphasises the performance of the building during its life – energy, water, internal environment, pollution, user comfort – rather than the upfront effect of the materials. In fact the Materials category accounts for only 14% of the total points obtainable.

In the case of the building materials, which as supplier of roof and wall cladding is the connection with NZ Metal Roofing Manufacturers Inc (NZMRM), there is an initial “cost” determined by the sustainability of the materials (inherent by manufacture and by waste) and a final “cost” determined at the end of life of the building and the eventual destination of the materials (reuse, recycle or waste). In the case of most products supplied by NZMRM members this consists of:


  1. Manufacture of the steel (before NZMRM) and delivery to MRM member
  2. Manufacture from this steel of the cladding products (NZMRM) and waste during manufacture
  3. Waste during the building process and recovery of this waste (after NZMRM)
  4. Recovery of cladding after building demolition and scrap, reuse, or recycle.

The path of these steps have been called - Steps 1 and 2 a) Cradle to Gate (i.e. before use); 1 to 4 b) Cradle to Grave; and 1 back to 1 is c) Cradle to Cradle. The environmental effects of the path depends on which of these it is. In the case of steel which is infinitely recyclable there is a big sustainability difference between paths b) and c), which is not always recognised. 

The Green Star programme is defined on the NZGBC website, but essentially it has been evolving stepwise since the beginning when it copied the Australian programme directly. The specific tool related to our purposes is “Green Star Design & As Built NZ”. Details are available on the NZGBC website so there is no need to repeat it all here, but in summary Green Star assesses the sustainability attributes of a project through impact categories. Each category groups a number of issues related to a certain sustainability impact; these are known as ‘credits’. Credits are weighted in relation to their assumed relevance to sustainability in the building, and to each other, by varying the number of points available. Each credit defines a clear aim along with specific criteria that a project must meet. Where the outcome is verified to have met the relevant criteria, available points will be awarded. 

Once all credits are assessed, the total number of points achieved is compared against the available points in the rating tool and a certified rating is awarded.

Under the Design & As Built Tool, projects are rated by Stars as follows - 

Note: Projects are only awarded a formal Green Star rating if they achieve 4 Stars or greater. 

So the realistic sustainability aim is for 4 or 5 Star performance. At one time (although no longer!) Government buildings in urban areas had to be 5 Star and in non-urban 4 Star. Could come back.

The programme started with Building Design only and has evolved to cover the entire building process as carried out, the interior and refits. 
So, how has NZMRM been involved in the ongoing development of the NZGBC programmes for Green Star and more recently Homestar?

Fletcher Building (who employed the author) was a founder member of the NZGBC. New Zealand Steel (NZS) followed shortly after, and during the 2000’s meetings between potential users and NZGBC to discuss the evolution of Green Star were attended regularly by people from MRM (as FB), NZS and HERA. NZMRM formed its own sustainability committee in 2005, which has met regularly since then. In 2009 NZMRM was a founder member of the first Sustainable Steel Council (associated with Metals NZ, and which was revitalised in 2019 after recess in 2015 and is now forging ahead). NZMRM is now a member of NZGBC in its own name, after being linked via some members and NZ Steel. 

Once the Sustainable Steel Council was formed we have worked with this forum to interact with the NZGBC rather than directly.

For much of this time we were working on the Mat-6 then Mat-8 Steel material credit and rollformed steel cladding products qualified under the Mat-8 criteria, but this has been revised in 2019. 

Several Mat-8 criteria no longer apply and in terms of the specifics of the Green Star Design & As Built Tool, the “Materials” Category now has 4 “Credits”. The credits where the use of products supplied by MRM members would apply are limited to:

Credit 19 Life Cycle Impacts: Two Alternative Pathways

  • 19A Life Cycle Assessment (max 7 points) 

Requires a whole of building, whole of life, Life Cycle Assessment to be conducted (MRM products may contribute but have little influence on this process)


  • 19B.2 Life Cycle Impacts - Steel (max 1 point)

Requires the use of minimum strength grades – use of G550 to allow 0.40 mm vs 0.55 mm steel 

Credit 21 Sustainable Products

  • Up to 3 points are available when a proportion of all materials used in a project meet some specified transparency and sustainability requirements.

A Reused materials - Items that have been previously used and are incorporated in the project without significant changes to the structure or function of the item

B Recycled materials - Items produced with recovered materials

C Environmental Product Declaration EPD - For product specific EPD it must be issued in conformance with ISO 14025 or EN15804; must be independently-audited; and must be based on a cradle-to-gate scope as a minimum.

D Third Party Certification - Several certification schemes have been assessed against the NZGBC Framework for Product Certification Scheme and meet the requirements for the Third Party Certification requirement in this credit.

E Stewardship Programmes - Product Stewardship Contract – Leased and purchased items. The supplier must agree to collect the item at the lease end for re-lease, re-use or recycling.

Credit 20 Responsible Building Materials

  • Note that supply from a responsible steel maker is no longer eligible for credits for steel cladding, and this now applies to structural steel and reinforcing only. 

Over the whole Green Star NZ programme it has been difficult for metal cladding made from steel produced in New Zealand to comply with the criteria. The most recent Design and Build criteria make compliance no more likely.

Green Star has always been aimed at the use of environmental principles in the larger units of building – offices, commercial buildings, schools etc (and has been successful in creating many sustainable buildings). This tool is not suitable for the more humble residential buildings – homes. 

“Homestar is a holistic tool to rate a home’s performance and environmental impact. A 10 Homestar rating recognises world leading standards for design, construction and efficiency in operation. A 6 Homestar rating recognises a home that has been built at or above the current standards set by the New Zealand building code, dependent on location across Aotearoa”.

Homestar was launched in 2010 as a fairly simple programme which had little or no reference to the materials used in the home. This meant that NZMRM was not able to gain any recognition for using steel or for its performance as a roofing material. It also meant that NZMRM was not as able to contribute as usefully in discussing the earlier versions as we were to Green Star. 

However, Homestar has evolved quite rapidly through version 2,3 and now 4, with Version 5 due in mid 2021.

As in the above description, Homestar emphasises and recognises the effect of the home environment and construction on the health and comfort of the occupants, rather than the effect on the environment, which is where NZMRM products can have an effect. 

In the current version 4, there is recognition for materials and specifically metal roofing in 4 areas and with 4 credits. These were covered in detail in the Scope 47 article in June 2018, but in summary the opportunities are in –

MAT-1 Sustainable Materials up to 10 points
– To encourage and recognise the specification and use of responsibly sourced materials that have lower environmental impacts over their lifetime. Points are available for both Wall Cladding and Roof Cladding as long as at least 50% of the material carries an approved eco-label. (Environmental Choice, Global Green Tag, EPD, etc.) 
WST-1 Construction Waste Minimisation up to 5 points -

– To encourage and recognise effective waste management practices by having a waste minimisation plan in place during construction and/or major refurbishment. To encourage and recognise a reduction in the amount of waste generated onsite during construction and/or major refurbishment. Metal cladding has minimal onsite waste compared to virtually all other materials. If any is generated it is usually separated and sent for recycling due to its high monetary value.

WAT-2 Sustainable Water Supply up to 4 points –

- To encourage and recognise reducing a dwelling’s demand on water supplies through the collection and use of rainwater on and around the dwelling. Collection of rainwater from a metal roof qualifies.

STE-1 Stormwater Management up to 4 points 

- To encourage and recognise houses/sites that reduce stormwater run-off from buildings and hard surfaces, in order to mitigate flooding, pollution and stream erosion. Collection of rainwater from a metal roof qualifies.

The suggested upcoming version 5 is looking to simplify the categories into Energy Efficiency, Healthy and Warm, Designed for People, and Caring for Nature. The emphasis however in terms of points allocation is still heavily weighted towards the Healthy and Warm aspects. 

While it is true that metal cladding is quite a small part of industrial buildings (somewhat more in residential), it does contribute to the overall sustainability of the building. This is recognised in the NZGBC rating tools; more so in Homestar than in Green Star.

Through continuous interaction with the NZ Green Building Council since its inception, NZMRM has been able to create recognition of this benefit to the entire construction. Now through Sustainable Steel Council Inc we will continue to do so. 
Thanks to Stuart Smith of NZ Steel for his GSAP input