Specifying efficient use of materials and considering their impact from manufacture to disposal.
The choice of materials for a project requires considerations of aesthetic appeal and initial and ongoing costs, life cycle assessment considerations (such as material performance, availability and impact on the environment) and the ability to reuse, recycle or dispose of the material at the end of its life.
Materials must be used sustainably – this means the present use will not compromise future use by running out or harming the environment at any time. Few materials fully meet this criteria. The aim when selecting materials should therefore be to use:
- materials from renewable or replaceable sources
- recycled materials
- materials that are in plentiful supply
- materials with a lower environmental impact across their whole life cycle.
Life cycle assessment considerations include:
- extraction and manufacture
- waste disposal/recycling/reuse
Extraction and manufacture
Impact of extraction: The environmental impact of extraction such as large-scale mining, on scarce, non-renewable resources is obvious, but even the extraction of renewable resources will have some impact on the environment. The effects of extraction may be:
- visual pollution
- air pollution
- water pollution
- chemical emission
- release of CO2
- damage to ecosystems
- water use
- energy use.
Energy and resource use: The total energy used in the extraction, production, transportation and construction of a building material is the embodied energy of that material. As high consumers of energy, buildings have a significant impact on our environment. Understanding embodied energy allows us to understand how much and where energy is used in the construction of buildings and the benefits of recycling.
Byproducts and emissions: The processes for the production of building materials can cause pollution and emissions of CO2 and other greenhouse gases.
Material sources: The source of materials must be considered to keep transport costs and resultant emissions to a minimum. The heavier or more bulky materials are, the greater the transport costs will be – where possible, heavy and bulky materials in particular should be sourced locally.
Availability: Availability may influence material selection decisions. Long delivery lead-in times must be allowed for as delays may cause project hold-ups and cost and energy losses.
Cost: Cost considerations must include the initial cost of purchase and the life cycle costs of materials. Life cycle costs include maintenance, replacement, demolition and disposal. Maintenance cost considerations must also factor in additional environmental costs such as the emission of volatile organic compounds (VOCs) when repainting.
Transport to site: The further materials must be transported, the greater the financial and emissions costs will be. Heavy or bulky products will have greater transport costs than lighter weight materials.
Health and safety during construction/installation: Some materials such as solvents and chemicals release VOCs, and materials that release dust and other airborne pollutants may be harmful to people during installation or application. Limit harmful effects by
- using paints, adhesives and primers that contain fewer harmful solvents
- providing good ventilation in spaces where LOSP treated timber is being used
- following the recommendations made by the manufacturer or supplier regarding installation or application.
Ease of construction/installation: Select materials and systems for ease of construction and installation. Complicated installations with close tolerances can result in greater wastage or even rework being required.
Adaptability: The design of any building and the materials selection should consider the future use or reuse of the building and use materials that facilitate adaptation or future replacement. The more adaptable a material, the less waste will result from changing needs or tastes.
Health and safety during the life of the building: Some materials give off emissions or allow run-off or leaching of chemicals that can be harmful to the health of building occupants. Adequate ventilation can mitigate some of the effects of gas emissions, but materials should generally be selected to minimise adverse effects to occupants.
Structural capability: Materials must be selected or designed for their ability to support the loads imposed by the building over the whole life of the building. An appropriate structural system and correct selection of structural materials can reduce excess material use and waste and increase the building’s adaptability for other uses.
Durability and maintenance: The Building Code sets minimum required levels of durability for different building elements, and this will be a primary driver for materials selection. Beyond this, durability and maintenance requirements should be considered together across the expected service life of the building. Some materials that do not appear to offer high levels of durability may actually perform well over many decades with the right maintenance. Timber weatherboards are a good example – where painted every 8–10 years, they can perform well for 60 years or more.
Materials that require little maintenance are not necessarily a better choice from an environmental point of view, particularly if their manufacture involves the release of large quantities of greenhouse gases. Materials that require more maintenance may turn out to be preferable if their original manufacture produced very few greenhouse gases.
There are a number of resources and tools available to help make these assessments:
- The BRANZ book Designing for maintenance
- The tools that are part of the Environment and zero carbon research.
BRANZ has also developed an Excel-based tool called LCAQuick that calculates the life cycle environmental impacts of composite building elements and whole buildings, taking into account maintenance and durability. The tool, aimed primarily at architects and designers, is available here.
Moisture resistance: Selected materials must be protected from moisture. Some materials have a natural moisture resistance while others must be fully protected from moisture.
Material deterioration/decay: Some materials deteriorate rapidly, particularly in a moist environment or if they are continuously wet, generally due to the growth of moulds or fungi, or corrosion of some materials, so it is essential that materials selected have the durability required for their area of use.
Thermal performance: Building design and material selection must contribute to good thermal performance and reduced energy demand by including insulation and thermal mass in the building. Building Code clause H1 Energy efficiency sets out minimum requirements for thermal performance but BRANZ recommends that the minimum requirements are exceeded wherever practicable.
Sound insulation: Building design and material selection must contribute to the sound insulation of the building, both from exterior noise and sound transmission within the building.
Fire performance: Building design and material selection must be in accordance with the requirements of Building Code clause C Protection from fire including fire compartment separations, allowing the occupants safe escape from the building and allowing fire service personnel safe access to the building. Materials must be selected for ignitability, surface spread of flame, fire loading, and fire resistance and stability.
Waste disposal/recycling and reuse
Reuse: Materials that can be reused after the useful life of the building will reduce the need for new materials to be produced in the future. How materials are installed and fixed can have an effect on the ability to reuse them, so the shorter the expected life of the building, the greater should be the reliance on screw or bolt fixing rather than adhesive and other permanent fixings.
Recycling: Materials that can be recycled will reduce the need for new materials to be produced, and the energy required to reconstitute materials is generally much less than required for new production.
Waste disposal: Building design and site management should aim to minimise waste, thereby reducing waste disposal and the release of pollutants. The impact of the disposal of materials at the end of their serviceable life must be considered.
Updated: 20 December 2020