Environmental Pro Forma for Green Architecture
Measures of Energy Consumption in Commercial Buildings and Homes
Apr 29, 2009
Materials like steel, glass and concrete used in the construction of buildings represent a financial investment and environmental cost. The upfront material costs include the purchase and processing of raw materials into building components like window frames and prefabricated walls. Materials must also be transported to the building site.
Each of these steps requires not only brute material, its transformation and human labour, but the input of non-renewable energy to render the material fit for use. Calculating the embodied energy in a green building recognizes the true cost to the environment of erecting architecture. Once the environmental costs have been factored in, it becomes easier to identify ways to diminish energy inputs and build more sustainably.
Two Types of Embodied Energy
Sustainability practitioners distinguish between initial embodied energy and recurring embodied energy.
Initial embodied energy refers to the cost to the environment in readying raw material for use in buildings. The easiest way to lower initial embodied energy is through building conservation and restoration.
Recurring embodied energy is related to the operation of a building. How much non-renewable energy does it take to heat and cool the building? How well will materials and building components perform over the life cycle or duration of a structure? If cheaper materials and components are installed initially, the building will incur ongoing expenses for maintenance and repair.
Poorly made components raise the operating costs. Window frames that perform badly have low R or insulation values and will undermine energy efficiency, making for more costly heating and cooling bills. An inadequately designed and installed roof can result in leaking and compromise the sustainability of the structure.
Measuring Embodied Energy
Embodied energy for architecture is usually expressed as megaJoules (MJ) or gigaJoules (GJ) per unit of weight (kg or tonne) or area (square metre). Included in the calculation of the embodied energy for different materials are a variety of ecological factors:
- Production of greenhouse gases in resource extraction, manufacturing and transportation
- Effects of environmental degradation, resource extraction and depletion
- Reduction in biodiversity
Researchers investigating life-cycle energy use in architecture have discovered the building’s structure, envelope (wall and roof systems) and mechanical services account for approximately equal amounts of embodied energy, about 25 percent each. Site work, construction and finishes compromise the other 25 percent.
A more difficult measure has to do with the environmental impact of different types of assemblies: steel construction versus wood or concrete, as an example. In principle wood construction has the lowest embodied energy, but in practice there may be little difference between the three in low rise construction, assuming that access to materials is equidistant and each is constructed in a similar climate.
In taller buildings, wood is not an option. Other factors come into play: whether there is a high degree of modularity for instance, reducing time and impact on the site and development costs. The likelihood of being able to recycle materials after their useful life is another consideration.
Redesigning the Building Pro Forma
Rating systems like LEED® encourage designers and developers to consider embodied energy in a building. Environmental assessment methodologies have been developed internationally to calculate embodied energy, using a variety of design tools and performance indicators for sustainability.
The pro forma used by developers in the past did not include costs to the environment for erecting buildings. Builders and developers of sustainable buildings are showing leadership by adopting more holistic approaches.
