Introduction to embodied energy
What is “embodied energy”? We talk a lot about saving energy, reducing cooling and heating costs for the home because these actions have the positive effect of reducing our carbon cost. In our search for efficiency, we should also know a big hidden cost of the a house is at its very beginning, before anyone even lives in it, it already has incurred a heavy carbon burden. This is the “embodied energy” – i.e. the energy that went into sourcing and processing raw materials and putting them together to build the home. In talking about “embodied energy”, it’s useful to have two numbers for reference: the average energy use of a home, and the amount of energy that goes into constructing a home.
Embodied energy: from raw material to a home is 280,000 kWh
At ShrinkThatFootprint our readers know that an average US household consumes 10,000 kWh of electricity every year. This number is not much different in European countries, Canada, Australia and New Zealand. It is lower in Asia, and as a rough rule, decreases as a function of GDP. On top of electricity, households use natural gas and propane as well for heating and running private generators.
The California Office of Historical Preservation cites CSIRO, an Australian government agency, for its estimates of “embodied energy” in a home. The estimate made by CSIRO was 1,000 gigajoules, equivalent to 278,000 kWh. Therefore, before anyone has even lived in home, the carbon cost of building the home is already at the amount of 278,000 kWh.
A new home has a carbon cost the same as 28 years of living in the home
Therefore, simply building the home uses 28 years worth of home energy before anyone has lived in the home. This expended energy into the “body” of the home is the “embodied energy”. Alas, this energy incurs an enormous carbon cost.
Imagine a house that’s 100 years old. Then the embodied energy is equivalent to 28% of that operational energy, which is a huge fraction of the energy. As technology makes our operational energy use more efficient, that embodied cost will also grow in importance. You might be interested in what comprises the embodied energy. Well, it’s many things.
- Harvesting timber
- Processing timber into lumber, or smelting the iron and processing it into steel
- Cutting timber into usable lengths and widths
- Transporting the materials to the work site
- Assembling materials into the structure of the home
- Making the home livable with urban infrastructure including roads, drains, water supply, power lines.
Each material has its own embodied energy
We mention lumber and steel, but every kind of building material will have its own embodied energy based on the energy cost of extraction and processing. To a degree, depending on where the mining or harvesting occurs, that embodied energy varies because the carbon intensity of the grid varies. In Scandinavian countries for example where use of renewables and nuclear is very high, presumably the embodied energy of materials will be lower. It’s not an accident that a large battery plant came online recently in Sweden.
Below we have placed a table with numbers from Australia’s CSIRO and the Californian Office of Historical Preservation that give estimates for embodied energy in different materials. Note that metals like aluminum and copper are very high at the topic, and even synthetic rubber. Woods, clay, concrete are at the bottom. Concrete may be very low in terms of energy intensity per kilogram, but the sheer mass of concrete used throughout the world means it has a huge impact on carbon emissions. So both the unit embodied energy for a material and the volume of its use dictate the impact on our carbon account.
|Material PER Embodied energy||MJ/kg|
|Plastics – general||90|
|Imported dimension granite||13.9|
|Laminated veneer lumber||11|
|Local dimension granite||5.9|
|Kiln dried sawn softwood||3.4|
|Kiln dried sawn hardwood||2|
|Precast steam-cured concrete||2|
|Precast tilt-up concrete||1.9|
|Air dried sawn hardwood||0.5|
Improving a home is better than building
High embodied costs for a new house means that anything we can to avoid it will benefit our carbon account. For example, instead of constructing a new home, staying in your home or making your home more energy efficient by adding solar, installing efficient appliances, and insulating it heavily is by far much better in terms of carbon costs.
Build from recycled materials to reduce embodied energy
There is however, one way to get to a new home with reduced embodied costs. On this site, we’ve talked about recycling or upcycling as being more carbon efficient. The reason is because recycling and upcycling avoid the cost of sourcing original, raw materials. At present, there’s no real standard way people use to build homes with recycled homes. For example it could be that one construction uses recovered timber from the previous house, and another construction uses recycled steel. Here are ideas for parts of the house that benefit from recycling:
Steel – Recycled
Scrap steel is available everywhere. Scrapyards make it a point to recover metal from discarded cars, appliances because it contains a lot of value. Steel beams, steel panels are very strong and if substituted for wood would easily displace a lot of necessary wood to yield the same strength. However, people don’t use steel in constructing homes in many places like North America and the UK. Steel tends to be used in skyscrapers.
Wood – Recycled, Composite
Firms turn recyclable plastics ed into little pellets. A refined process applies great heat to melt and mix the pellets with shaved wood. The resulting product is a particulate wood material. When a high pressure machine heats and compresses the particulate material at enormous pressures it turns the particulate wood into a plank! Wood composite has disadvantages to regular wood. It is denser and more brittle. On the other hand it is also very rigid and strong, and resistant to wood rot and mold.
More ways to reduce embodied energy use
Given what we know, the key to reducing carbon in a new house by reducing embodied energy use is to find a sweet spot between low maintenance durability, energy efficient, and cost-efficient materials. There are times these requirements conflict with each other. For example, particle board is made from recycled wood, but itself is difficult to recycle because it contains fillers like resin, plastics. Here we list out our tips for low embodied energy use:
- Ensure materials can be easily separated so repairs are easy to carry out
- Build the smallest house comfortable to you to save on building materials
- Upgrade or renovate instead of demolishing, building new
- Divert waste materials from demolition to be reused or recycled
- Use locally sourced building materials as much as possible to avoid transport carbon impact
- From the start, pick low embodied energy materials such as recycled or upcycled materials
- Emphasize waste reduction during the build phase
- Pick building materials that are easy to recycle after use, for example avoid particle board
- Bias toward use of materials made using renewable energy
- Insulate, insulate, insulate! This reduces reliance on heating and cooling systems
- Reduce water flow needs to downsize water pipes
Anna Lauer is a writer, gardener, and homesteader living in rural Wisconsin. She has written for Mother Earth News, Grit, and Hobby Farms magazines. Anna is writing a new book about growing your food for free and an ultimate guide to producing food at little to no cost. When she’s not writing or gardening, Anna enjoys spending time with her husband and two young daughters.