Choices of materials and construction methods can significantly change the amount of energy embodied in the structure of a building, as embodied energy content varies enormously between products and materials.
Embodied energy is the energy consumed by all of the processes associated with the production of a building, from the mining and processing of natural resources to manufacturing, transport and product delivery.
A complex combination of many processed materials each contributing to the building’s total embodied energy. The single most important factor in reducing the impact of embodied energy is to design long life, durable and adaptable buildings. Renovation and maintenance also add to the embodied energy over a building’s life.
Buildings are a big contributor to climate change. There are two ways in which buildings are responsible for greenhouse gases:
1. The construction phase.
Buildings are made of concrete and steel, producing a lot of emissions when they’re being made. The largest impact on the emission of CO2 is by far the embodied carbon within the groundworks.
2. During the ongoing operations.
It’s natural to think of lights and appliances like TVs as the biggest energy hogs, but they’re not: It’s actually heating and cooling. Operational carbon will reflect your energy supply solution as well as the efficiency of the house itself. The best solution, from a climate point of view, is to electrify as much as we can. As we use cleaner sources of electricity and make buildings more efficient, the emissions from construction materials will represent a larger share of the total. Given the volumes of insulation required for a low energy construction, the choice of insulation type will have a significant impact on overall embodied carbon.
Using timber solutions like CLT (Cross Laminated Timber) should only be used where the strength of CLT is needed and not elsewhere. CLT that replaces steel or concrete is not the answer, especially where lightweight steel construction or small section timber will do.
It’s understandable that the perceived environmental benefit of CLT is key to the enthusiasm. However, it is a simplification to say that wood stores CO2 and thus it is a perfect material.
Assessing the embodied energy of a material, component or whole building is a complex task. Embodied energy is not occupant dependent, the energy is built into the materials. Operational energy consumption depends on the occupants. Embodied energy content is incurred once (apart from maintenance and renovation) whereas operational energy accumulates over time and can be influenced throughout the life of the building. Embodied energy content varies greatly with different construction types. A higher embodied energy level can be justified if it contributes to lower operating energy. As the energy efficiency of houses and appliances increases, embodied energy will become increasingly important.
Materials with the lowest embodied energy, such as concrete, bricks and timber, are usually consumed in large quantities. Materials with high energy content such as steel are often used in much smaller quantities. Often it is more useful to think in terms of building components and assemblies rather than individual materials. Comparing the energy content per square meter of construction is easier for designers than looking at the energy content of all the individual materials used.
Guidelines for reducing embodied energy
Each design should select the best combination for its application based on climate, transport distances, availability of materials and budget, balanced against known embodied energy content.
– Design for long life and adaptability, using durable low maintenance materials.
– Use an efficient building envelope design and fittings to minimize materials.
– Ensure materials can be easily separated.
– Avoid building too big – and save materials.
– Select materials that can be reused or recycled easily.
– Modify or refurbish instead of demolishing or adding.
– Avoid wasteful material use and specify standard sizes to avoid using additional materials as fillers.
– Use locally sourced materials to reduce transport.
Reuse of building materials commonly saves about 95% of embodied energy that would otherwise be wasted!!
Adams, Connor and Ochsendorf 2006: Embodied energy and operating energy for buildings: cumulative energy over time. Design for sustainability.
Lawson 2006: Embodied energy of building materials, Environment design guide.
Bill Gates: Buildings are bad for the climate.
Jae Cotterell: Passivhouse and embodied energy – how important is it?
The Sierra Club: Open letter.