by Wayne B. Trusty
Designing, constructing, and operating an environmentally friendly building is more complex than it seems, especially when it comes to selecting the right materials. As much as people enjoy rules-of-thumb for the selection process, the reality is that one is constantly forced into a balancing act, trading off a good effect here with an undesirable outcome there.
While a number of available ‘tools’ help determine appropriate green materials, it can be difficult to decide which tool is best for the task at hand. Unlike other design and construction resources, the green building toolkit can seem arcane and its components easily confused. However, by using a simple classification system, it can becomes clear how they interrelate and fit into the overall green building design process.
One of the better tools is life-cycle assessment (LCA), which provides essential data and measures. LCA is an increasingly important methodology for making decisions throughout the entire design process—from programming through detailed design to specification and procurement.
Numerous other tools are also at the design team’s disposal during the project delivery process. The trick is in determining which are most appropriate and when and how they fit into building assessment systems, like the Leadership in Energy and Environmental Design® (LEED®) rating system developed by the U.S. Green Building Council (USGBC).
The tools classification system
A simple, tri-level classification scheme helps position resources in terms of their focus, intent, and use in various phases of the project delivery process.
These tools focus on individual products or simple assemblies (i.e. floor coverings and window systems) and are used for making comparisons based on environmental and/or economic criteria. Examples of the most common tools include the Building for Environmental and Economic Sustainability (BEES) software program and the GreenSpec Directory.
An LCA-based tool developed by the U.S. National Institute of Standards and Technology (NIST), BEES software is designed to make product-to-product comparisons based on LCA and life-cycle cost (LCC) data. It uses a weighting system to combine disparate environmental measures into one score that can be charted against cost.
The GreenSpec Directory discusses the environmental merits of individual products based on criteria developed by the publishers of Environmental Building News. Organized according to the Construction Specifications Institute’s (CSI’s) MasterFormat™ 1995 (MF95), it provides detailed product listings for more than 1,650 products in 250 categories, with guide specifications for each product category to indicate benefits, drawbacks, and environmental considerations.
TerraChoice Environmental Services Inc.’s Environmental Choice Program (ECP) and various forest certification systems could be classified in Level One, but many of them focus on single attributes or performance measures (i.e. energy use or recycled content). As such, they may provide misleading green information; the product in question may very well excel in terms of specific criteria selected for evaluation, but might not score well in an LCA or multi-tiered evaluation system.
Rather than dealing with individual products, these tools focus on an entire building or its complete assemblies (i.e. walls, floors, and roof). Level-Two resources provide decision support in areas such as LCC, operating energy, or life-cycle environmental effects. Data-oriented and objective, they apply from the conceptual through detailed design stages. Operating energy simulators and daylighting analysis tools fall under this category.
Here, the Athena™ Sustainable Materials Institute’s Environmental Impact Estimator (EIE) software is particularly relevant. It is the only Level-Two tool in North America assisting with material selection within the context of a building’s entire life cycle, capturing implications of product selection and design options related to its structure and envelope.
These tools are whole-building assessment frameworks, or systems encompassing a broader range of environmental, economic, and social concerns, or other issues considered relevant to sustainability. They blend objective and subjective inputs, and lean on Level Two tools for much of the objective data (i.e. energy simulations). All of these resources use subjective scoring or weighting systems to distil information and provide overall measures—all of which can be used to guide the design process.
LEED, the National Association of Home Builder’s (NAHB’s) Model Green Home Building Guidelines, and the Green Building Initiative’s (GBI’s) Green Globes are perhaps the best-known Level-Three tools in the country. These resources apply to new projects, existing buildings, and major renovations/retrofits. Some require external auditors, and most certify or label a building’s performance. They can be used for a wide range of building types, from residential and commercial to institutional and light industrial.
Other tools, systems, and sources
The tools mentioned above are examples of what is available under each category, but there are many other sources for product details and green building-sustainability information. Some Web sites provide design guidance and specific technical information, while other whole-building assessment systems are used in the United States and elsewhere.
To decide which tool is most suitable for the task at hand, one must establish clear and important distinctions by asking several questions:
- Does it work on the level of whole buildings or focus more on individual products/components?
- Does it deal with a specific topic or concern, such as energy consumption, or cover a broad spectrum of sustainability issues?
- Is it quantitative or does it include subjective/qualitative elements?
- These distinctions are often ignored, and comparisons are sometimes made between dissimilar systems intended for entirely different purposes. BEES and EIE are complementary, for example, and can meet different needs at different stages in the project delivery process. They are not competing tools between which one must choose.
A closer look at BEES and EIE Software Programs
BEES and EIE provide life-cycle information for different purposes and in different ways. It is useful to take a closer look at the two—their use, methodology, and underlying intent in the design and delivery process.
Building for Environmental and Economic Sustainability (BEES)
BEES provides users with direct comparisons between environmental performance and life-cycle cost, making the results from trade-offs clear.1 The program uses importance weights to combine environmental and economic performance measures in a single performance score (although the user can select a No Weighting option). The user decides how to weight environmental/economic performance (e.g. 50/50, 40/60), and selects from four alternative weighting systems for the performance measures (two of which were developed by scientific panels). The program also lets users change the default discount rate used for calculating the present value of life-cycle costs.
The current version of BEES includes approximately 200 building products/variations, about 80 of which are brand specific. For example, the category for ‘slab-on-grade’ has 10 generic product variations and six brand-specific types. Floor Coverings has 17 distinct generic products and 18 brand-specific ones. The generic data covers representative production technology or an aggregative result based on average U.S. technology for the relevant industry.2
Environmental Impact Estimator (EIE)
As noted earlier, EIE enables architects/engineers (A/Es) and researchers to assess the environmental implications of building designs at an early stage in the project delivery process. By working on a whole-building level, EIE captures the system’s implications of product selection related to a building’s structure and envelope.
The tool currently covers three specific areas in the United States (as well as eight in Canada) and a U.S. average, and lets users account for the embodied effects of original material manufacturing, transportation, and installation, as well as maintenance/replacement over a building’s assumed life cycle. (Where relevant, it distinguishes between owner-occupied and rental facilities.) The building’s life is selected by the user and can be varied to assess relative durability effects.
EIE also lets users compare the embodied effects of a material’s production/use against operating energy-use estimates (developed separately using simulation software). As a result, operating energy emissions and pre-combustion effects (i.e. the energy and emissions associated with making and moving energy) are taken into account.
Incorporating Athena’s life-cycle inventory database for about 100 generic structural and envelope materials, EIE simulates over 1000 different assembly combinations. In fact, it is capable of modeling the structure and envelope systems for about 95 percent of the building stock in North America. Results are provided for detailed environmental flows to/from nature, and in the form of six summary measures. The user can make side-by-side comparisons of up to five alternative designs for each summary measure. These comparisons can be among variations on a base case or include completely different projects, in which case comparisons are best made on a unit floor-area basis.
Picking the right tool
To understand how BEES and EIE fit into a complementary suite of sustainable building resources, one has to focus on the kinds of questions the tools answer, and the information required at different stages in the project delivery process. The user must also be conscious of the difficulty in maintaining functional equivalence when comparing building materials.
Maintaining functional equivalents
In LCA-based comparisons, the term ‘functional equivalence’ refers to the challenge of ensuring two or more products provide the same level of service. This is not easily accomplished in building applications because the specification of one material may necessitate the selection of certain other products. For example:
- wood, steel, or concrete structural systems will likely influence, or even dictate, the choice of insulation materials;
- an above-grade structure using high-mass materials may require more concrete in footings than a lighter structural system; and
- a rigid floor covering may require a different substrate than a flexible one.
In all these examples, product comparisons should take into account the material-use implications of the alternatives. In other words, comparisons must be made in a ‘building systems’ context, rather than on simple ‘product-to-product’ bases. Even though two products may appear equivalent in terms of a specific criterion, such as load-bearing capacity, they may not be at all equal in the sense of true functional equivalence. In a similar vein, one must remember to take into account all the components required during construction to install a particular product. Mortar and rebar go hand-in-hand with concrete blocks; fasteners, tape, and taping compound are integral to gypsum wallboard; nails are an essential component of wood-stud walls.
Fortunately, not all products pose a functional equivalence problem to the same degree. Generally, product-to-product comparisons are more likely to be misleading when dealing with structure and envelope materials, where the systems context is key. Product comparisons are more realistic with the move to interior finishes, fit-out products, and furnishings.
For example, resilient or flexible floor coverings can be readily compared to each other, provided installation materials, cleaning products, expected service life, and results at the end of a product’s life are all taken into account. However, part of the envelope, even window systems—which are typically delivered to a construction site as pre-assembled components—can be compared to one another in terms of thermal performance or other criteria without too much regard for broader systems implications.
In short, one must think in terms of a continuum, with systems-oriented products at the structural end of the scale and more standalone products at the interior fit-out end. The trick is exercising caution and accurately assessing the legitimacy of every comparison.
Different questions at different stages
The tools explored above (and those not covered here) address distinct questions throughout the various stages of the design process. As such, one has to consider the data most suitable for each tool.
EIE should be used at the conceptual design stage where significant environmental effects are often locked in by basic structure and envelope decisions. At this early stage, the A/E makes critical and sometimes irreversible decisions, so he requires good (albeit generic) information about the relative effects of materials, components, or design alternatives. Seldom is there concern at this point over final product choices and sources. Indeed, many of the critical elements in conceptual design are in the nature of commodities with relatively low brand differentiation.
In contrast, BEES comes into play at the specification/procurement stages of project delivery, where brand-specific information becomes more important. Indeed, this kind of data is essential for product categories with highly disparate environmental performance. As Level One and Two resources, EIE and BEES both serve critical needs at different stages in the project delivery process, and can serve as valuable inputs for Level Three tools, such as LEED, Green Globes, or the Model Green Home Building Guidelines.
1 The direct ‘economic-versus-environmental’ comparison is only one way in which BEES software allows users to view comparative results for different products. Findings can also be analyzed by life stage and environmental ‘flows’ (which show how substances like ammonia (NH3), hydrogen chloride (HC), and sulfur oxides contribute to acid rain) for 12 performance measures.
2 A number of manufacturers participated in the ‘BEES Please’ program to provide brand-specific data.
About the Author
Wayne B. Trusty is president of the Athena™ Sustainable Materials Institute in Merrickville, Canada. He can be reached by calling (613) 269-3795 or via e-mail at email@example.com.
Life-cycle assessment (LCA) is a methodology for assessing the environmental impact of a product over its ‘cradle-to-grave’ or ‘cradle-to-cradle’ (in the case of recyclables) life span.
Performance is generally measured over a wide range of criteria, such as global warming and the depletion of both fossil fuels and the ozone layer—indicators of the environmental loadings resulting from a product’s manufacture, use, and disposal. Although these indicators do not directly address an item’s impact on the health of people or their ecosystems, they do provide a good measure of environmental performance (given that reducing any of these effects is a step in the right direction).
In LCA, the effects associated with making, transporting, using, and disposing products are referred to as ‘embodied effects,’ where ‘embodied’ refers to attribution or allocation in an accounting sense as opposed to true physical embodiment. The building community tends to refer primarily to embodied energy, but all flows to/from nature are embodied, and further effects are associated with the production and transportation of energy itself (known as ‘pre-combustion effects’).
While the energy required to operate a building greatly overshadows the energy attributed to the products used in its construction, other embodied effects, such as toxic releases into the world’s water resources, are almost entirely a function of resource extraction, manufacturing, and transportation. As such, the essence of life-cycle assessment is to cast the net wide and capture all of the relevant effects associated with a product or process, including the manufacturing and use of other materials required for maintenance.
LCA is not the same as life cycle costing (LCC). The two methodologies are complementary: LCC focuses on the dollar costs of building and maintaining a structure over its life, while LCA focuses on the environment. Performance is measured in the units appropriate to each emission type or effect category.