Embodied Energy
The embodied energy in a house is the total energy required to build it. That includes the extraction, mining etc. of the raw materials, processing and manufacturing them and transporting them to the site and assembling them.
As an extremely rough rule of thumb the embodied energy in contemporary houses might be in the region of a tenth of that used during the lifetime of a house so it is much less important than the ‘in use’ energy, but nevertheless important. With better insulation and reduction of in-use energy the proportion of embodied energy becomes more significant. The energy used to produce building materials can be found at the Sustainable Energy Research Team at the University of Bath.
There is quite a good Australian government web site on the subject
The embodied energy of building materials varies enormously, e.g. aluminium is extremely energy hungry in its manufacture whereas at the opposite extreme, straw bales are extremely low. Timber is also low and has the added bonus of locking up carbon for the duration of the building’s lifetime.
The principle is to use the high energy materials as little as possible and only when nothing else will do. An example of this would be a range windows made by Nordan, which are basically very high quality timber but use a small aluminium drip section fixed at the bottom of the glazing unit to shed water away from the lower edge.
The embodied energy is measured in MJ/Kg so it is important to take into account the density of the material. For instance expanded polystyrene has very high embodied energy but is very light so using it for insulation is not as bad as it might initially seem.
The challenge with concrete
Probably one of the biggest challenges concerns the use of concrete which is not only very energy intensive in its manufacture but also emits large amounts of carbon dioxide, as limestone (calcium carbonate) is converted to calcium oxide. The outstanding quality of concrete (apart from its structural strength) is its ability to stay in contact with water without rotting or rusting. Hence its almost universal use in foundations. There may eventually be ways round this more +/-»
Another high energy material is glass and there are some issues about how often double or triple glazed units fail (by leaking and fogging up) and how much energy they actually save if you have to replace them regularly.
Some of the traditional ways of house building are extremely low in embodied energy. An example is cob (using the earth available locally and mixing it with straw) of which there are about 70,000 examples, mainly in the South West of England.
There can be occasional surprises. On first thoughts a living roof , be it turf or sedum, might seem to have less embodied energy than say a clay tile roof where the tiles have been fired in a kiln which uses a great deal of energy. However, when you do the sums you find that the waterproof membrane beneath the living roof may well contain the same embodied energy as the tiles because of the high energy, oil based material it is made of.
Embodied energy tables can also be found here
