Story: Building materials

Page 5. Steel, aluminium, plastics and insulation

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Steel is a mainstay of modern construction. Its great strength in proportion to its dimensions makes it invaluable in multi-storey construction, where control of height is a key factor in the number of floors which can be built. Building height affects the profitability of many projects.

New Zealand is earthquake-prone, and steel frames are particularly useful to achieve earthquake-resistant construction. Steel can also strengthen existing buildings. Steel speeds up construction because steel elements can be prepared in a factory or workshop, complete with protective paint coatings, ready for delivery and assembly at the site.

Pre-cambered floors


Floor panels and beams are usually pre-cambered – curving upward in the middle so they will settle at the correct level under their own weight, and that of any concrete poured over panels to form a finished floor.



From the 1970s building relied heavily on aluminium. It can be moulded into complex profiles of almost any length. Special aluminium strips are available to join materials, and to form edges, gratings, grilles and trays.

Aluminium window frames transformed the appearance of large buildings, and the methods of constructing them. In domestic buildings aluminium joinery almost completely replaced timber for doors and windows. The material can be pre-coated in a heat-cured paint coating, or it can be electrically anodised to achieve a semi-gloss metallic finish.

High-rise curtain walls

In a curtain wall, aluminium window frames are bolted directly to a high-rise structure to create a sheer wall of glass. The frame itself may be part of the architectural design of the exterior, or it may be concealed behind the glass. Modern curtain walls have to be capable of resisting earthquakes and strong winds – tall buildings flex considerably under these forces.


After packaging, the building and construction industry is the second-largest consumer of plastics in New Zealand. There are many forms of plastic, all with particular building applications. Plastics can be moulded into useful shapes such as pipes, valves, gratings, plumbing fixtures, panels, doors, windows, and fittings such as baths.

Build your house out of polystyrene


In the 1990s and 2000s a system of building using polystyrene blocks and sheets for cladding became popular in New Zealand. This required a bit of a shift in thinking – for most people polystyrene was a packaging material also used to make cheap chilly bins and children’s surfboards. And its use as a wall cladding has not been without problems – while the material is not to blame (it is an excellent insulator), if it has been poorly installed or designed, moisture that has penetrated or collected on the inside face of the polystyrene cladding cannot escape. Trapped water can lead to rot in the internal timber framing.


Plastic’s durability and resistance to chemicals means it is used for carrying fresh water, waste water, and many kinds of chemicals. Its light weight makes handling and installation easy. Many plastic pipes carrying wires and fluids are concealed within walls.


Buildings are mainly insulated by inclusion of lightweight materials. Insulation comes in many forms including metallic foils, fibrous blankets and plastics, and combinations of these. Foils include very thin aluminium bonded to heavy paper. Blankets use a wide range of fibres, including wool, polyester, dacron and fibreglass. The most common plastic insulation is expanded urethane (polystyrene) which is supplied in thick sheets or can be placed in liquid form in a structure, where it rapidly expands and fills cavities before drying.

How to cite this page:

Jeremy Salmond, 'Building materials - Steel, aluminium, plastics and insulation', Te Ara - the Encyclopedia of New Zealand, (accessed 21 June 2024)

Story by Jeremy Salmond, published 11 Mar 2010