Embodied Energy – Is It Important?

Embodied energy of building materials

In my most recent book, Making Better Buildings, one of my objectives was to quantify the “embodied energy” of a wide range of building materials. Embodied energy refers to the amount of energy input to harvest and transport raw materials and process them into building components, and our conventional approaches to building tends to use a lot of materials with very high embodied energy. It has always been my goal to choose materials with the lowest possible embodied energy, which reduces the impact of the building on the planet.

Embodied energy of building materials

Embodied energy in building materials is no small matter!

In doing the research for the book, I was surprised to find a large number of sustainable building commentators who completely dismiss the importance of embodied energy in building greener homes. The argument is that the amount of embodied energy is relatively small compared to the amount of operating energy used by the building over its lifespan. Depending on who’s doing the analysis, embodied energy (EE) can be anywhere from 1/20 to 1/50 of lifetime operational energy. Therefore, the thinking is that EE isn’t really that important.

As the figures in the illustration above make abundantly clear, we use a crazy amount of energy making our buildings. Reducing this figure makes a lot of sense, especially when it is relatively easy to make material choices that can reduce EE by several orders of magnitude with little or no affect on the price or energy efficiency of the building.

Paying attention to EE makes sense in an immediate and visceral way, too. While projecting the lifetime energy use of a building is a valuable exercise, we have no way of knowing how much – or what type – of energy will actually be consumed in that building. But we know for certain that the energy used to produce materials and make buildings is being consumed right now. We know that it’s almost certainly fossil fuel energy that’s being used, and we know that the resulting carbon and other pollutions associated with that energy is entering the atmosphere right now. And we know that it is a large, concentrated amount of energy being used, likely within a year or two of the building being made. At a time when we are concerned about carbon levels in our atmosphere, the EE of buildings is low-hanging fruit. We can have a serious and meaningful impact at this level.

The choices aren’t that difficult to make. For example, the owner of a 1,000 square foot home wants to insulate the attic space. Up for consideration are three different insulation types: cellulose, mineral wool and fiberglass. All will have the same impact long-term energy reductions in the building, but look at the difference in EE figures:

  • Cellulose:  963-5,452 MJ (depending on source of cellulose)
  • Mineral wool: 14,691 MJ
  • Fiberglass: 26,040 MJ*

In gasoline equivalents, the low figure for cellulose represents 8 gallons of gas, while the figure for fiberglass represents 217 gallons! One small decision on the part of a homeowner can make a 200+ gallon difference! If you multiply that over the many decisions to be made in a single home, and then again by the number of homes and renovations that happen, this is no small amount of impact that we can make immediately by paying attention to EE. We don’t need to sacrifice the energy efficiency in the long term to have dramatic impacts right now.

Here’s another interesting example. The owner of a new straw bale house is trying to decide between different kinds of plaster. The choices won’t have any impact on energy efficiency, since the bales will provide the same level of insulation regardless of the plaster type. Look at the difference between choosing a clay plaster over a cement-based plaster:

Embodied energy comparison from the book Making Better Buildings

Embodied Energy comparison from Making Better Buildings

Again, one decision can save seven times the amount of EE!

Another problem with ignoring EE in favour of long term energy efficiency is that we cannot predict how much energy a building will use over its lifetime, or how long that lifetime will be. If, in 20 years, that home is using 100% renewable energy, then its EE suddenly represents the majority of its impact on the planet. We are also making large strides in reducing overall energy use, with PassiveHouse and other such programs showing that we can build at or close to net zero energy homes. For a net zero energy home, the EE of its materials and construction can represent the majority of its impact, so why not lower that impact?

Any builder or owner who willfully chooses to ignore EE as an important factor in making a greener building is doing so with blinders on. The choices are easy to make, the research is easy to access, and the resulting building does not have to perform any less efficiently. Choosing high EE materials is willfully neglectful, and in my experience the choice is often due to sheer laziness or an unwillingness to alter choices simply because that’s what has always been done. A builder doesn’t need to dabble on the fringes of the natural building world to drastically reduce EE. Many mainstream choices offer vastly lower EE than others. It’s just a matter of putting the effort into knowing what the EE impacts will be.

Ann Edminster, in her 1995 paper Investigation of Environmental Impacts of Straw Bale Construction, compared the EE of a conventional home versus an intentionally low-impact home of similar size and amenities.  What she found was that “The embodied energy for the conventional frame house was 509,000 KBtus. The embodied energy for the low impact straw bale house is 41,000 KBtus, or about one twelfth that of the frame house.”

If we can consciously make cost-effective, energy efficient decisions that lower our EE impacts by up to 12 times, there is no excuse to not be doing this!

*All figures from the Inventory of Carbon and Energy (ICE) V.2, University of Bath