Story: Building materials

Page 6. Roofing and glazing

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Corrugated iron

Corrugated iron (more correctly, steel) was invented in Britain in the 1820s. Strong and cheap, it rapidly became the characteristic roof for New Zealand buildings, and sometimes walls. It was available as early as 1843. It was imported in large quantities, and often auctioned at ports.

Baby iron

 

A miniature form of corrugated iron was also developed, which was known variously as sparrow or baby iron, and used mainly for walls and small roofs. It has also been widely used as a roof and wall covering for industrial and rural buildings, and in the manufacture of water storage tanks for properties without access to reticulated water.

 

Because steel rusts, sheets were galvanised by dipping them in molten zinc. The zinc coating oxidised in the air, preventing rust. Flashings covering junctions were folded out of plain galvanised sheet, with lead strips attached to the edges which could be pressed down into the shape of the corrugations. Lead-capped nails were hammered through the peaks of corrugations to hold the roof down – the lead caps prevented water entering the nail holes. Lead is poisonous, so it is no longer used on roofs that are used to collect water for consumption. A modern substitute known as flashguard has been developed for these roofs.

Until the 1980s corrugated iron was the most common roofing material, but it has been substantially superseded by aluminium-coated steel products such as Zincalume. It is claimed that these have better corrosion resistance.

Ceramic tiles

 

Most state houses of the 1930s and 1940s were built with concrete or ceramic roofing tiles rather than the more usual corrugated iron. This was to encourage local ceramic tile manufacturing, under a policy known as import substitution. New Zealand had a ceramics industry but not a steel industry.

 

Slates and tiles

The earliest tiles were stone, including slate – a type of stone split into very thin layers. Slate is long lasting, but expensive because of the high labour costs of extraction, shaping and fixing. Originally, much slate was imported from Britain – particularly Wales – but high-quality slate was also found in New Zealand. In the early 2000s slate was imported from China, Spain and the US.

In Australia and New Zealand ‘Marseilles’ tiles (fired clay tiles that interlock) became popular in the early 1900s because of their ease of fixing and comparative lightness. Originally imported from France, these were eventually manufactured in Australia. Later, similar tiles were made from concrete cast in moulds.

The weight of tiles and slate requires more framing than an iron roof. Tiles pressed out of metal became popular – they imitate the look of tiles but do not require the same framing.

Glass

Glass for windows has always been imported into New Zealand, and in the early days, when it was comparatively expensive, it was sold in small panes, about 300 by 250 millimetres. Windows in most houses were divided into multiple squares – if one pane broke, the cost of replacement was not too high. Only very large, expensive houses had sash windows made of a single piece of glass.

Floating glass

 

Until about the mid-1800s imported glass was hand-made. Air was blown into a ball of molten glass, which gradually expanded forming a long cylinder. This was cut and allowed to lie flat. Modern glass is made by pouring the molten glass onto a bed of molten tin to give an almost perfectly flat surface. This is called float glass.

 

Coloured glass

Coloured and patterned ‘fancy’ glass was used in some doors and windows. The earliest examples were formed using ‘flash glass’ – a very thin layer of brightly coloured glass was attached to ordinary clear glass, and decorative patterns could be cut through the coloured layer with grindstones or using acid.

After about 1900 the use of leadlight became popular. This technique had been used in churches for centuries. Coloured glass was cut into shapes and joined with a moulded lead strip (a cane) to make elaborate patterns or pictures.

Modern glass

In the early 2000s glass was used in many forms and applications. It is no longer a fragile and brittle material, and may be given great strength in the manufacturing process – structural glass can be completely self-supporting by using adhesives or stainless steel suspension systems. Glass blocks combine the structural properties of glass with the convenience of masonry construction.

New Zealand energy-saving standards now require the use of double glazing, which significantly reduces the amount of heat lost through glass.

How to cite this page:

Jeremy Salmond, 'Building materials - Roofing and glazing', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/building-materials/page-6 (accessed 22 March 2019)

Story by Jeremy Salmond, published 11 Mar 2010