If we want to reduce the total environmental impact of a building, we must consider the impact of the materials that have gone into its construction. Clearly no house can claim to be an eco-house if it is constructed from materials that had a major environmental impact elsewhere.

For these reasons, the concept of embodied energy is central to good environmental design. The embodied energy of a building material is the energy that has been required to extract, process, and manufacture it and then to transport it to the building site. The embodied energy in the structure of a new house is considerable, exceeding the total energy required to heat that house for the next 20 years.

In terms of the energy of manufacture, the highest embodied energy is found in metals (steel requires 57,000kWh to produce one cubic metre), and highly processed industrial products (hardboard and MDF require 2,000 kWh to produce 1m3). The middle range of materials are simpler to make but require a lot energy in their manufacture (bricks and concrete blocks need 700kWh/m3). The lowest embodied energy is in materials that require only simple processing (building timber needs 180kWh/m3 ) or those made from salvaged materials or local natural materials, which require virtually no energy.

The issue of embodied energy divides new eco-buildings into two distinct families. One kind of eco-building aims to obtain the lowest possible energy consumption with the most efficient available technology, such as high performance insulation and solar panels. Such buildings have a high embodied energy which they hope to justify with large savings in their energy consumption, or even to generate and export a surplus of energy. The other kind of eco-building aims to achieve the lowest possible embodied energy by using salvaged materials or simple local materials (straw bales, rush matting, mud bricks). Such buildings will usually perform less well in terms of annual energy consumption, and are less durable, but often have a lower overall environmental impact over the course of their lifespan.

Embodied energy is usually a good guide to wider environmental impacts, especially for toxic waste and atmospheric pollution. There are two main exceptions to this:
Cement and Concete, which has a mid range emobodied energy, but a disproportionately high impact on climate change. When limestone is burnt to make lime it releases an equal weight in carbon dioxide. Taken as a whole, the cement industry produces 5% of the worlds human carbon dioxide emissions.
Timber has a low embodied energy, but can have a very high environmental impact if taken from old growth forests.