5.2 EMBODIED ENERGY
- Embodied energy and operational energy
- Assessing embodied energy
- Embodied energy of common materials
- Guidelines for reducing embodied energy
Embodied energy is the energy consumed by all of the processes associated with the production of a building, from the mining and processing of natural resources to manufacturing, transport and product delivery. Embodied energy does not include the operation and disposal of the building material. This would be considered in a life cycle approach. Embodied energy is the ‘upstream’ or ‘front-end’ component of the lifecycle impact of a home.
This fact sheet discusses the relationship between embodied energy and operational energy. It then discusses the embodied energy of common building materials and guidelines to consider when reducing embodied energy impacts.
The single most important factor in reducing the impact of embodied energy is to design long life, durable and adaptable buildings.
Every building is a complex combination of many processed materials, each of which contributes to the building’s total embodied energy. Renovation and maintenance also add to the embodied energy over a building’s life.
Choices of materials and construction methods can significantly change the amount of energy embodied in the structure of a building. Embodied energy content varies enormously between products and materials. Assessment of the embodied energy of a material, component or whole building is often a complex task.
It was thought until recently that the embodied energy content of a building was small compared to the energy used in operating the building over its life. Therefore, most effort was put into reducing operating energy by improving the energy efficiency of the building envelope. Research has shown that this is not always the case.
Embodied energy can be the equivalent of many years of operational energy.
Operational energy consumption dependes on the occupants. Embodied energy is not occupant dependent – the energy is built into the materials. Embodied energy content is incurred once (apart from maintenance and renovation) whereas operational energy accumulates over time and can be influenced throughout the life of the building.
Research by CSIRO has found that the average household contains about 1,000 GJ of energy embodied in the materials used in its construction. This is equivalent to about 15 years of normal operational energy use. For a house that lasts 100 years this is over 10 percent of the energy used in its life.
Embodied energy content varies greatly with different construction types. In many cases a higher embodied energy level can be justified if it contributes to lower operating energy. For example, large amounts of thermal mass, high in embodied energy, can significantly reduce heating and cooling needs in well designed and insulated passive solar houses.
[See: 4.5 Passive Solar Heating; 4.6 Passive Cooling; 4.7 Insulation; 4.9 Thermal Mass]
As the energy efficiency of houses and appliances increases, embodied energy will become increasingly important.
The embodied energy levels in materials will be reduced as the energy efficiency of the industries producing them is improved. However, there also needs to be a demonstrated demand for materials low in embodied energy.
Whereas the energy used in operating a building can be readily measured, the embodied energy contained in the structure is difficult to assess. This energy use is often hidden.
It also depends on where boundaries are drawn in the assessment process. For example, whether to include:
- The energy used to transport the materials and workers to the building site.
- Just the materials for the construction of the building shell or all materials used to complete the building such as bathroom and kitchen fittings, driveways and outdoor paving.
- The upstream energy input in making the materials (such as factory/office lighting, the energy used in making and maintaining the machines that make the materials).
- The embodied energy of urban infrastructure (roads, drains, water and energy supply).
Gross Energy Requirement (GER) is a measure of the true embodied energy of a material, which would ideally include all of the above and more. In practice this is usually impractical to measure.
Process Energy Requirement (PER) is a measure of the energy directly related to the manufacture of the material. This is simpler to quantify. Consequently, most figures quoted for embodied energy are based on the PER. This would include the energy used in transporting the raw materials to the factory but not energy used to transport the final product to the building site.
In general, PER accounts for 50-80 per cent of GER. Even within this narrower definition, arriving at a single figure for a material is impractical as it depends on:
- Efficiency of the individual manufacturing process.
- The fuels used in manufacture of the materials.
- The distances materials are transported.
- The amount of recycled product used, etc.
Each of these factors varies according to product, process, manufacturer and application. They also vary depending on how the embodied energy has been assessed.
Estimates of embodied energy can vary by a factor of up to ten. As a result, figures quoted for embodied energy are broad guidelines only and should not be taken as correct. What is important is to consider the relative relationships and try to use materials that have the lower embodied energy.
Precautions when comparing embodied energy analysis results
The same caution about variability in the figures applies to assemblies as much as to individual materials. For example, it may be possible to construct a concrete slab with lower embodied energy than a timber floor if best practice is followed.
Where figures from a specific manufacturer are available, care should be exercised in making comparisons to figures produced by other manufacturers or in tables that follow.
Different calculation methods produce vastly different results (by a factor of up to ten). For best results, compare figures produced by a single source using consistent methodology and base data.
Given this variability it is important not to focus too much on the ‘right’ numbers, but to follow general guidelines.
Precise figures are not essential to decide which building materials to use to lower the embodied energy in a structure.
Typical figures for some Australian materials are given in the tables that follow. Generally, the more highly processed a material is the higher its embodied energy.
|MATERIAL||PER EMBODIED ENERGY MJ/kg|
|Kiln dried sawn softwood||3.4|
|Kiln dried sawn hardwood||2.0|
|Air dried sawn hardwood||0.5|
|Laminated veneer lumber||11.0|
|Plastics – general||90|
|Imported dimension granite||13.9|
|Local dimension granite||5.9|
|Precast steam-cured concrete||2.0|
|Precast tilt-up concrete||1.9|
Source: Lawson Buildings, Materials, Energy and the Environment (1996);
* fibre cement figure updated from earlier version and endorsed by Dr. Lawson.
These figures should be used with caution because:
- The actual embodied energy of a material manufactured and used in Melbourne will be very different if the same material is transported by road to Darwin.
- Aluminium from a recycled source will contain less than ten per cent of the embodied energy of aluminium manufactured from raw materials.
- High monetary value, high embodied energy materials, such as stainless steel, will almost certainly be recycled many times, reducing their lifecycle impact.
CSIRO research has found that materials used in the average Australian house contain the following levels of embodied energy:
Materials with the lowest embodied energy intensities, such as concrete, bricks and timber, are usually consumed in large quantities. Materials with high energy content such as stainless steel are often used in much smaller amounts. As a result, the greatest amount of embodied energy in a building can be either from low embodied energy materials such as concrete, or high embodied energy materials such as steel.
|ASSEMBLY||PER EMBODIED ENERGY MJ/m²|
|Elevated timber floor||293|
|110mm concrete slab on ground||645|
|200mm precast concrete T beam/infill||644|
|Timber frame, concrete tile, plasterboard ceiling||251|
|Timber frame, terracotta tile, plasterboard ceiling||271|
|Timber frame, steel sheet, plasterboard ceiling||330|
Source: Lawson Buildings, Materials, Energy and the Environment (1996)
For most people it is more useful to think in terms of building components and assemblies rather than individual materials. For example, a brick veneer wall will contain bricks, mortar, ties, timber, plasterboard and insulation.
|ASSEMBLY||PER EMBODIED ENERGY MJ/m²|
|Single Skin AAC Block Wall||440|
|Single Skin AAC Block Wall gyprock lining||448|
|Single Skin Stabilised (Rammed) Earth Wall (5% cement)||405|
|Steel Frame, Compressed Fibre Cement Clad Wall||385|
|Timber Frame, Reconstituted Timber Weatherboard Wall||377|
|Timber Frame, Fibre Cement Weatherboard Wall||169|
|Cavity Clay Brick Wall||860|
|Cavity Clay Brick Wall with plasterboard internal lining and acrylic paint finish||906|
|Cavity Concrete Block Wall||465|
Source: Lawson Buildings, Materials, Energy and the Environment (1996)
Comparing the energy content per square metre of construction is easier for designers than looking at the energy content of all the individual materials used. The table above shows some typical figures that have been derived for a range of construction systems.
Lightweight building construction such as timber frame is usually lower in embodied energy than heavyweight construction. This is not necessarily the case if large amounts of light but high energy materials such as steel or aluminium are used.
There are many situations where a lightweight building is the most appropriate and may result in the lowest lifecycle energy use (eg. hot, humid climates, sloping or shaded sites or sensitive landscapes).
In climates with greater heating and cooling requirements and significant day/night temperature variations, embodied energy in a high level of well insulated thermal mass can significantly offset the energy used for heating and cooling.
There is little benefit in building a house with high embodied energy in the thermal mass or other elements of the envelope in areas where heating and cooling requirements are minimal or where other passive design principles are not applied.
Each design should select the best combination for its application based on climate, transport distances, availability of materials and budget, balanced against known embodied energy content.
Guidelines for reducing embodied energy:
- Design for long life and adaptability, using durable low maintenance materials.
- Ensure materials can be easily separated.
- Avoid building a bigger house than you need. This will save materials.
- Modify or refurbish instead of demolishing or adding.
- Ensure materials from demolition of existing buildings, and construction wastes are reused or recycled.
- Use locally sourced materials (including materials salvaged on site) to reduce transport.
- Select low embodied energy materials (which may include materials with a high recycled content) preferably based on supplier-specific data.
- Avoid wasteful material use.
- Specify standard sizes, don’t use energyintensive materials as fillers.
- Ensure off-cuts are recycled and avoid redundant structure, etc. Some very energy intensive finishes, such as paints, often have high wastage levels.
- Select materials that can be re-used or recycled easily at the end of their lives using existing recycling systems.
- Give preference to materials manufactured using renewable energy sources.
- Use efficient building envelope design and fittings to minimise materials (eg. an energy efficient building envelope can downsize or eliminate the need for heaters and coolers, water-efficient taps allow downsizing of water pipes).
- Ask suppliers for information on their products and share this information.
Re-use and recycling
Some materials such as bricks and roof tiles suffer damage losses in re-use.
Re-use of building materials commonly saves about 95 per cent of embodied energy that would otherwise be wasted.
Savings from recycling of materials for reprocessing varies considerably with savings up to 95 per cent for aluminium but only 20 per cent for glass.
Some reprocessing may use more energy, particularly if long transport distances are involved.
Life Cycle Assessment
Life Cycle Assessment (LCA) examines the total environmental impact of a material or product through every step of its life – from obtaining raw materials (for example, through mining or logging) all the way through manufacture, transport to a store, using it in the home and disposal or recycling.
LCA can consider a range of environmental impacts such as resource depletion, energy and water use, greenhouse emissions, waste generation and so on.
LCA can be applied to a whole product (a house or unit) or to an individual element or process included in that product. It is necessarily complex and the details are beyond the scope of this fact sheet. An internationally agreed standard (ISO 14040) defines standard LCA methodologies and protocols.
|BEDP Environment Design Guide
PRO 2 Embodied Energy of Building Materials
|Lawson, B (1996) Building Materials, Energy and the Environment: Towards Ecological Sustainable Development, RAIA, Canberra|