Metal Roofing In New Zealand: A History
With an estimated market share of around 70%, New Zealand has one of the highest percentages of prepainted and roll formed long run metal used in roofing in the world.
So how has our love affair with what is commonly called “tin roofs” developed? To help us try and understand, first we need to look back at a little history of how “tin roofs” first evolved.
There are examples of iron sheeting being used for roofs in Europe and the US as far back as the early 1800’s with it being used as a cheaper alternative to copper and lead.
It does seem to be generally accepted that “corrugated iron” was first patented in 1829 in London, with the corrugations added to flat sheets of iron to provide added strength that allowed a greater span over a lighter framework thus helping reduce costs.
Tin roofs, which were seen as a lighter alternative to “iron” roofs weren’t widely accepted until after the US Civil War (circa 1865) when “tin” rolling mills were established and tin plate shingles were introduced.
Whilst the term “tin roof” is now a very generic term, originally tin roofs were in fact made from iron plated with tin, a naturally occurring silvery coloured soft metal. One of the first to use tin plate roofing on his now historic home, Monticello in Virginia USA was Thomas Jefferson who as we know was one of the founding fathers and an author of the US Declaration of Independence.
Another reference to “tin roofs” was Terne plate, which is fact wasn’t tin, but iron that was coated in an alloy of lead (65%) and tin (35%), giving it a duller finish and claimed greater durability. It’s not known if Terne plate was ever used in New Zealand, but there is no doubt that the high lead content would today cause significant environmental concerns with water run off and water collection.
Zinc coated iron or steel (commonly referred to galvanised iron) was first introduced in the 1830’s in France and started to gain popularity due to its longevity as a result of the zinc providing a sacrificial coating that protected the iron underneath the coating.
One of the early notable buildings to have a galvanised iron roof was the US Mint located in New Orleans whereby the zinc coating was applied to 20 gauge (0.8mm) corrugated iron. By comparison, today’s typical base metal thickness for a roof is 0.55 mm thick.
As we moved further into the 19th century, technology of the day started to take over and there was a progression away from the naturally occurring iron, to melting it at high temperatures (1,700°C) in the presence of oxygen and coke to form steel which has significantly greater tensile strength, yield and is significantly tougher.
The early settlers to New Zealand saw “corrugated iron” as an easy to use, practical and versatile product that was used in the construction of early homes and buildings around the country, with it being seen by some as being right at the inception of our “do it yourself” Kiwi culture. Early examples of “corrugated iron” construction can be found in Central Otago dating back to the 1840’s.
Durability, longevity, recyclable and low maintenance coupled with a move in the 1960’s to local roll forming equipment manufacturers and specialised roll forming businesses started to open helped develop and grow what we now know as “long run metal roofing and cladding” industry.
With the opening of the NZ Steel mill in 1968 and then a further upgrade in 1987, the installation of a galvanising pot allowed for locally produced galvanised steel roofing materials to be supplied into the market. These came in a range of differing coating weights often defined by the preface “Z”, with common coating weights including 185 gsm and 275 gsm.
Established in 1917 and now part of the Fletcher Building stable of companies, Pacific Coilcoaters then became the first producers of continuous “coil coating” or painting of pre-painted long run metal roofing products in the mid 1980’s and the launch of the ColorCote® brand in 1989. Up until that point all long run metal roofing products were left unpainted to “weather” or were post painted after installation.
Further steel technology developments saw the introduction of what is commonly referred to as AZ or aluminium / zinc coatings in 1969, with global manufacture in the 1970’s.
These coatings provided better weathering protecting than the traditional pure zinc (Z) coatings at a lower cost and often lower overall weight. AZ metallic coatings are typically defined as having a composition of 50-60% aluminium, 1-2% silicon, and the remainder zinc. AZ coating weights were typically in the 150 - 200 gsm coating weight range and this technology quickly became the “bread and butter” metallic coating used across the industry with it being produced locally by NZ Steel from around 1993.
As we know, New Zealand has an extensive coastline with many of our towns and cities exposed to harsh environmental conditions from salt spray and the resulting corrosion. As a result, in the mid 2000’s the use of a new metallic coating called ZAM® was introduced by ColorCote®. Developed in Japan by Nippon Steel in 2000, ZAM® provided superior salt spray and scratch corrosion resistance SCOPE 61 than the tradition AZ and Z coated steel substrates through the addition of magnesium that allows any scratches or minor cut damage to “self heal”.
This new metallic coating was comprised of 6% aluminium, 3% magnesium and the balance (circa 91%) in zinc and was designated by the preface ZM or ZMa ZAM® was marketed and sold under the brands ZM8® and more latterly MagnaFlow™ by ColorCote®.
In the mid 2000’s there was yet another development to help enhance the durability of long run metal products with the advent of AM or aluminium / magnesium based metallic coatings. These coatings allowed for yet more improved durability whilst using lower coat weights.
Typically containing 47-57% aluminium, 1-3% magnesium, & 1-2% silicon with the balance comprising of zinc, AM coatings were first introduced into the New Zealand market as another performance improvement under its ColorCote® MagnaFlow™ brand in 2016.
As the focus continues to increase on sustainability and the environmental impact of all construction related products, so given that steel production emits approximately 7% of worlds total CO2 emissions, the manufacture of steel-based products including roofing and cladding falls under the spotlight.
Whilst steel is effectively 100% recyclable, the next generation of metallic coated steel development will not only focus on more efficient methods of manufacturing and recycling steel using electric arc furnaces, but also the choice of Hydrogen to replace the use of Coke to help decarbonise the steel.
This new chapter in steel manufacture alongside continuous future developments in metallic coating technology will ensure that roll formed prepainted long run metal roofing and cladding will continue to be seen as the most efficient, durable and economical choice in the construction industry for many more years to come.
