Building materials in new houses

This Issue This is a part of the Building materials feature

By - , Build 107

If you were asked which building materials comprised the greatest percentage of new houses, what would you say? Like life, it depends on how you look at it.

Figure 1: Exemplar house – materials by weight.
Figure 2: Exemplar house – materials by embodied energy.
Figure 3: Market share of materials in new houses.

Materials from which houses are built change over time. Some interesting trends emerge from analysing the quantities of different types of building materials in new houses. For example, although timber framing still has a high market share (88%), this is a 10% drop over the past 8 years.

Looking at how much of one material goes into a home varies, depending on the criteria used. Here, we look at new housing materials from three different perspectives:

  • materials by weight
  • materials by embodied energy
  • market share of materials.

Quantity very one-sided

The quantities of materials in a typical new house are shown in Figure 1. These quantities are for the ‘exemplar house’, a 2-storey house on a concrete slab, with clay brick cladding and a steel roof. The total floor area, including the garage, is 195 m2.

Figure 1 shows percentage by weight and, as expected, the hardfill for the floor and the concrete slab are by far the major proportion, followed by the cladding. All the other components combined make up less than 20% of the total.

Energy ups and downs

When we look at the embodied energy of the materials, the proportions are somewhat different. Embodied energy is the sum of all the energy used to manufacture the materials, including extraction of raw materials and their transport to the manufacturing plant. Some materials such as aluminium, glass, plastic products and fibreglass insulation are quite energy intensive to produce. For these materials, their proportional share increases by a factor of 10 or more (see Figure 2).

Figure 1: Exemplar house – materials by weight.

Operating energy use in a house is currently several times the embodied energy over its life, but as energy costs rise, there are incentives to use less operating energy. Thus the embodied component will become more significant.

Materials such as glass, aluminium and plastics are difficult to substitute and will continue to be required. Glass use will actually increase with the introduction of mandatory double glazing, but, in the long term, double glazing results in net gains due to increased space conditioning energy savings. The same applies for insulation, solar panels using plastic tubing and well designed use of concrete as a heat sink. These materials can save operating energy use in certain applications.

Trends in material use

The most common materials by weight in Figure 1 include concrete, timber framing, clay brick cladding and steel roof cladding. The market share trends for each of these are shown in Figure 3.

Figure 2: Exemplar house – materials by embodied energy.

Timber started at about 98% framing share in 2000 but has lost ground to concrete masonry, light steel, polybloc and wood based panels.

The new housing concrete floor share allows for upper storeys with timber floors normally. Concrete’s share of total floor area has fluctuated around 80% in recent years.

Figure 3: Market share of materials in new houses.

Sheet steel roofing (excluding metal tiles) is steadily increasing its market share.

Clay brick has had the largest share of all claddings in new housing in recent years, but now appears to be losing some ground to timber and fibre-cement weatherboards.

Where the numbers come from

The figures for the market share of materials are derived from the BRANZ materials survey. BRANZ receives approximately 500 returns each quarter: 300 for new housing, 100 for alterations and additions to housing, and 100 for non-residential buildings. The survey forms identify particular buildings chosen at random from building consent lists published by Building Consent Authorities. Respondents (builders and designers) fill in the types of materials used including flooring, framing, wall and roof claddings, insulation, windows, linings and other components.

The survey has been underway for 10 years and provides data unavailable elsewhere.

For more

If you would like to find out the market share and market size trends for your products, please contact Ian Page at BRANZ, call (04) 237 1170 or email [email protected].

For details of the exemplar house see ‘The Exemplar House – A specific example of residential costing’ by R. Wilson, 2002.

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Figure 1: Exemplar house – materials by weight.
Figure 2: Exemplar house – materials by embodied energy.
Figure 3: Market share of materials in new houses.