Your home leaves an environmental footprint beyond its carbon emissions from daily energy consumption. Two other factors carry great weight: the embodied energy in its materials, and the durability of the structure.
Embodied energy is the sum of energy inputs a material requires over its lifetime. Several organizations have proposed indexes of embodied energy that allow comparison among building materials. Not everyone agrees on what inputs should be included in these indexes, making comparisons difficult. But most such indexes account for the energy consumed in some or all of these activities.
Mining or harvesting the raw materials.
Shipping the raw materials to the manufacturing facility.
Processing the raw materials into building products.
Shipping the materials to the job site.
Installing the building materials.
Performing needed maintenance over the material’s lifetime.
Disposing of or recycling the material when it is replaced or the building is demolished.
Calculating an accurate amount of embodied energy is difficult. For example, should embodied energy include the energy required to build the manufacturing facility? Should embodied energy include the energy required to build the vehicle used to transport the material? What about the energy used by house builders to commute to the job where the material is installed?
The longevity of a material must also be considered when assessing its environmental impact. For example, PVC plastic roof gutters that last for ten years or less cannot be compared pound-for-pound to PVC plastic plumbing that remains functional for fifty years or more. And if a material is recycled when the building is demolished—common for aluminum in today’s market but not for concrete—then some or its embodied energy is reclaimed by recycling.
Certain materials deserve special praise for using recycled materials or low-impact raw materials. These special materials include the following.
Cellulose insulation made from ground newsprint.
Plywood with a sawdust core.
Oriented strand board made from wood chips.
Floor trusses utilizing small diameter timber.