Defining the carbon footprint of a building is an elusive and complex process. Unlike individual products that have well-defined shelf lives and finite ingredients, buildings stand for decades, endure climatic extremes and will be used for multiple purposes.
Every decision that goes into the design, material choice and energy use in a building has a long-term effect. "Buildings are the most long-lived products we make," says Tom Gloria, chief knowledge officer for eQuilibrium Solutions Corporation, a sustainable management services company in Boston.
Their longevity makes getting an accurate life cycle assessment (LCA) complicated. LCA is a method of holistically evaluating the environmental impact of a product throughout its life cycle, from the harvesting of raw materials through processing, manufacture, installation, use, and ultimately disposal or recycling or the entire envelope.
As a method for new building construction, LCA could be used to compare the environmental benefits or detriments of options available to the design team, Gloria says. "LCA statistics give you a snapshot in time about where materials came from and how they will perform."
To date, however, there is no easy system for clearly defining the true life cycle of such a long-term structure. "Buildings are very different at the end of their life than at the beginning," he points out, "and LCA tools today don't handle that level of complexity."
While the industry has yet to perfect a system for evaluating the LCA of buildings, it also is embracing the concept and using it at more points throughout the decision-making process from the assessment of individual materials to whole building evaluations. "The construction industry is getting a crash course in life cycle assessment, and manufacturers are beginning to use LCA to substantiate product claims," Gloria points out.
The U.S. Green Building Council is also embracing life cycle assessments and is working to incorporate LCA into its LEED certification program to better quantify the global impact of buildings, says Brendan Owens, vice president of LEED Technical Development in Washington, D.C. In the current LEED system, individual points are given for sustainable material features, such as using renewable sources, recycled content, or local harvesting but USGBC believes it is time to take the LCA process to the next level.
"The key to LCA for buildings is moving beyond single attributes of individual materials, and taking a more global view of the whole package," Owens says.
This is particularly important to help developers get beyond choosing materials for one good attribute without looking at how that choice affects the whole project. "You can make a good decision at one viewpoint that creates problems at another," Owens says. For example, a material might include recycled content but it also has to be shipped from China, which results in significant carbon offput in transportation; or it may offer the lowest carbon option, but has ecotoxicity problems.
"There is a litany of products out there that are good at one thing but you need to look at what else can happen if you choose them," he says. "Multiple attribute screening can help you make more holistically informed decisions."
Finding the Balance
To support that holistic approach, LEED is developing a life cycle assessment-based credit system. In January 2007, The USGBC Life Cycle Assessment working group developed initial recommendations for incorporating LCA of building materials as part of the LEED Green Building Rating System. Owens notes that USGBC is currently working to phase out single criteria point systems and phase in the LCA approach.
"The level of education about LCA is increasing and it's a good time to incorporate an alternative compliance path that takes a more holistic view," he says of the decision.
The ability to conduct life cycle assessments for buildings is becoming more realistic as data about building materials is gathered and software tools are released to help contractors and architects weigh the long-term impacts of their decisions.
Taking that 'pros and cons' approach is critical right now, says Wayne Trusty, president of the Athena Sustainable Materials Institute and Athena Institute International, two nonprofits in Canada and the U.S. dedicated to sustainability of the built environment. "There won't ever be a perfect solution or an absolute number for the LCA of buildings," he says. "What you can get however, is a reasonable estimate of the impact of your choices so that you can focus on the differences."
Using LCA data and software tools, developers can compare choices to improve their 'base case' he says. Trusty's group has developed Ecocalc, a free downloadable software tool for LCA assessments (www.athenasmi.ca) that lets users change parameters, such as base size, material choices or sourcing options to compare the global impact of certain decisions.
"It lets the design team get immediate answers without all the onerous research," Trusty says.
These kinds of tools promise to make LCA for buildings far more realistic, says Phaedra Svec, AIA LEED AP, an associate in the Elements division of BNIM Architects in Kansas City, Mo.
Svec spent her early years at BMIN collecting a library of data on materials used by her firm to help designers make more informed life cycle decisions. "I have a deep respect for the science of LCA," she says. "When it happens for a building it's wonderful, but it's rare that architects incorporate that level of assessment into their work."
Svec felt frustrated early on by the complexity of trying to assess the LCA of a building when so many variables came into play. She tried a number of early tools, including BEES (Building for Environmental and Economic Sustainability) software, beta versions of Ecocalc and others to establish broad carbon footprints of her projects and compare decisions, such as whether to use steel or concrete at the super structure level.
BNIM used an early LCA tool for its decision making process on the School of Nursing and Student Community Center at the University of Texas Health Science Center in Houston, which it built in 2003. One of the primary outcomes of its LCA evaluations was how BNIM used concrete in the project and, in some cases, replacing steel because the data showed concrete had a smaller footprint in that scenario.
"It helped us understand how to optimize the structure, but we also learned that the software at that time was too cumbersome. It required complicated computations and a lot of interpretation," she says. "It helped us with the big decisions but it didn't help with the details."
That project also helped Svec realize that effective LCA tools must be regionalized so that they can take into account issues such as locally grown and harvested materials, climate impact and the effect of purchasing decisions on the nearby economy.
Seven Steps for LCA
In the absence of software tools that could deliver quick and effective life cycle assessments for buildings, Svec developed her own seven-step 'material filter' method for evaluating and comparing the life cycle of building materials. "It's not a scientific method," she quickly admits. "Rather it gives us some judgment behind our decisions and helps us ask the right questions."
She notes that every material -- no matter how green -- has an environmental consequence. "It's about comparison, and choosing the material with the least impact."
Svec envisions the seven-step method as a series of narrowing filters, with the criteria at the top (No. 1) representing the largest impact a material choice has, and those at the bottom (No. 7) representing the smallest.
1. Energy and water used in the building
Does the product or assembly reduce the energy and water consumption of the building over its lifetime? </b>
"This is the single greatest impact of the project," Svec says. She gives the example of using windows with glazing made in China over those produced locally. "If the glazing from China results in less energy used over the building's 100 year life cycle, you may pick it over a less energy efficient material made locally," she points out.
These criteria can outweigh all others when looking at the environmental impact of a building over the course of its life, so it should be carefully considered up front in the design process.
2. Environmental and Human Health Systems
Does the product or assembly throughout its lifecycle reduce the negative impact on life-support systems?
Svec urges developers to consider the impact of their building choices on air, atmosphere, water, ecosystem, habitat and climate. This includes the generation of hazardous by-products and pollution by the materials themselves, as well how the materials are extracted and processed, and the carbon dioxide that results from its transportation to the job site. "This is where you have to look at where a product is manufactured and how it is manufactured," she says, noting that much of this information can be gathered from the distributors and manufacturers.
In this category it's important to look beyond greenwashing. "You have to look up-stream and down-stream at the human health and degradation issues to make an informed decision," she says.
3. Occupant Wellbeing
Does the product or assembly eliminate hazards to indoor air quality, while improving indoor environmental quality, and occupant wellbeing?
PVC is excellent example of this filter. "A window covering dipped in PVC may deliver excellent shading, which impacts energy use," she says. "However, every time the sun hits it causes toxic off-gassing."
In this real-life example, Svec searched hard for an alternative window covering and pushed her suppliers to find a solution. Eventually one of them developed a new product to meet her needs. "That's the power of this process," she says. "It's gets us all talking about better solutions."
4. Durability, Performance & Maintenance
Does the product or assembly perform its intended function elegantly for at least 100 years?
This is a classic selection criterion for any building, Svec notes, adding that durability and maintenance play a key role in the lifelong impact of a material. "Everyone talks about new products made from tires, sawdust, or recycled paint, but if you have to replace them every few years or use four times as much material to achieve the same results, they are not sustainable."
5. Recycled Content
Is the product or assembly produced with recycled material stock reducing the demand for virgin raw materials?
This is one of the most popular criteria for green building. It's easy to assess because most materials manufacturers tout their recycled content, and it's an excellent measure of the savings of virgin material.
6. Resource Limitation
Is the product or assembly made from materials that are rapidly renewable or are they rare and endangered?
An example of this category is hard wood used for floors or structures, she notes. This criteria also is easy criteria to assess, and in most cases, there are alternative materials available to replace those that don't meet this requirement.
7. Waste Management
Is the product or assembly produced in a way that limits the generation of solid waste, and is the materials itself reusable or recyclable at the end of its useful life in the building? Does the material disassemble and separate into recyclable components?
The Sourcebook for Green and Sustainable Building estimates that 8,000 pounds of waste are typically thrown into landfills during the construction of a 2,000 square-foot home. To offset this, Svec urges developers to assess waste that results from packaged materials used in the construction of the building, and to look into whether the manufacturer is making efforts to reduce waste at their own plants.
"The seven steps can be cumbersome at first but if you use it, you'll start to make better choices without compromising quality," she says. "The key is to ask more questions about where materials come from, how they are made, and how long they will last. Those answers will allow you to think more clearly about the full impact of your decisions, and soon you develop an instinct for it."
In the meantime, software tools, databases and a greater knowledge of LCA applications are making it easier for the industry to take a holistic long-term approach to sustainability.
"These tools will allow developers to optimize the whole building," says Owens. "They promise to change the way we all look at what we do."
Sarah Fister Gale is a freelance writer based in Chicago.
Building photo licensed under the Creative Commons by Le Jhe.