Designing, constructing and operating environmentally friendly buildings can be a lot more complex than it seems, especially when it comes to materials selection. We would all like simple measures or rules of thumb that would make the selection process easy, but they are hard to come by, if they exist at all. The reality is that we are constantly forced into a balancing act, trading off a good effect here with a not-so-desirable outcome there. Fortunately, there are a variety tools that can help.
However, it does not help that the general clutter and confusion in the green building scene often makes it difficult to decide on the right tool for a task at hand. The problem is further complicated because, unlike other design and construction tools, the sustainable building tools may seem arcane and are easily confused. This article tries to bring a degree of order by presenting a simple system for classifying sustainable, or ‘green', building tools and establishing how tools interrelate, and where they fit in the green design process.
The article especially focuses on two complementary tools, BEES (Building for Environmental and Economic Sustainability) and the Athena Environmental Impact Estimator (EIE) that have been designed to provide the building community with ready access to essential life cycle assessment (LCA) data and measures. LCA is a methodology that is increasingly important for making decisions throughout the entire process, from conceptual through detailed design, specification and procurement (see Sidebar). In addition to an overview of the two tools and how they complement each other, the article discusses when they are best used by design teams during the project delivery process, and how they fit with building assessment systems such as LEED Ô .
LCA is a methodology for assessing the environmental performance of a product over its full life cycle, often referred to as cradle-to-grave or cradle-to-cradle analysis. Environmental performance is generally measured in terms of a wide range of potential effects, such as fossil fuel depletion, global warming, or ozone depletion. All are measures of indicators of the environmental loadings that can result from the manufacture, use and disposal of a product. The indicators do not directly address the ultimate human or ecosystem health effects — a much more difficult and uncertain task — but they do provide good measures 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 of products are referred to as ‘embodied effects', where the word embodied refers to attribution or allocation in an accounting sense as opposed to true physical embodiment. In the building community, the tendency is to refer primarily to ‘embodied energy', but all of the extractions from and releases to nature are embodied effects, and there are also embodied effects associated with the production and transportation of energy itself (known as pre-combustion effects).
While the energy required to operate a building over its life greatly overshadows the energy attributed to the products used in its construction, other embodied effects such as toxic releases to water, are almost entirely a function of resource extraction, manufacturing and transportation activities. The point is to beware of the common tendency to focus only on embodied energy. The essence of LCA is to cast the net wide and capture all of the relevant effects associated with a product or process over its full life cycle, including the production and use of other products required for cleaning or maintenance.
LCA is not the same as life cycle costing (LCC). The two methodologies are complementary, but LCC focuses on the dollar costs of building and maintaining a structure over its life cycle, while LCA focuses on environmental performance. Performance is measured in the units appropriate to each emission type or effect category. For example, global warming gases are characterized in terms of their heat trapping effects compared to the effects of CO2, and global warming potential is measured in equivalent tonnes of CO2.
2. A Tool Classification System
This simple tool classification system helps position BEES , the Environmental Impact Estimator and other tools in terms of their focus, intent and use in various phases of a project delivery process. The system suggests three main levels of tools, labeled simply as Level 1, 2, and 3 tools.
Level 1 tools focus at the individual product or simple assembly level (e.g., floor coverings or window assemblies) and are used to make comparisons in terms of environmental and/or economic criteria. These are probably the most common tools. BEES and GreenSpec Directory may be especially relevant for architects:
• BEES is an LCA based software tool developed by the U.S. National Institute of Standards and Technology, and designed to make product-to-product comparisons based on LCA and LCC data. It uses a weighting system to combine disparate environmental measures into one score that can be charted against cost.
• GreenSpec Directory is a guide to environmentally preferential building products, produced by Building Green (the publishers of Environmental Building News), and offered in book form and through an on-line web site subscription. The Directory provides detailed product listings for more than 1,650 products in 250 categories, organized according to the CSI MasterForma tÔ system, and helps readers understand the environmental merits of individual products based on a set of criteria developed by the publishers. GreenSpec also provides guideline specifications for each product category, indicating the benefits, drawbacks, environmental considerations, and generally what to look for in a green product within a given category.
One could argue that labeling systems like the Environmental Choice program, operated by Terra Choice, and various forest certification systems are also Level 1 tools. The caution is that many labeling programs focus on single attributes, or performance measures (energy use or recycled content, for example), and may therefore be misleading when they convey a ‘green' label. The product in question may indeed be excellent in terms of the criteria selected for the evaluation, but that does not necessarily mean it would score well in a full LCA, or in a system that takes more attributes into account.
Level 2 tools focus on the whole building, or complete assemblies, providing decision support in specific areas of concern such as life cycle costs, operating energy, or life cycle environmental effects. They are data-oriented and objective, and apply from the conceptual through detailed design stages. Operating energy simulators and daylighting analysis tools fit in this category along with life cycle costing.
Athena's Environmental Impact Estimator is particularly relevant here because it is the only Level 2 tool in North America that assists with material selection in the context of life cycle assessment of an entire building. Rather than dealing with individual products, it focuses at the level of whole buildings or complete building assemblies (walls, floors and roofs, for example) and therefore captures the systems implications of product selections related to a building's structure and envelope. The Estimator and BEES are complementary, with the Estimator more appropriately used at the conceptual design stage, and BEES at the specification or procurement stage of project development.
Level 3 tools are whole building assessment frameworks or systems that encompass a broader range of environmental, economic and social concerns or issues considered relevant to sustainability. They use a mix of objective and subjective inputs, leaning on Level 2 tools for much of the objective data — energy simulation results, for example. All use subjective scoring or weighting systems to distill the information and provide overall measures, and all can be used to inform or guide the design process.
LEED and BREEAM Green Leaf are currently the best-known Level 3 tools in Canada , with Green Globes, a derivative of BREEAM Green Leaf, rapidly becoming established as the successor to its parent. Currently available Level 3 tools may apply to new projects, to existing buildings, and to major renovations or retrofits. Some require external auditors, and most yield certificates or labels indicating a building's performance. They can be used for a wide range of building types, from residential to commercial, institutional and light industrial.
2.1 Other Tools, Systems and Sources
The tools mentioned above are only representative and certainly do not exhaust the list for each category. For example, there are other sources of information on products, and there are excellent web sites that provide design guidance as well as specific technical information. There are also other whole building assessment systems used in the U. S. and elsewhere.
The point is to establish some clear and important distinctions. Does a tool work at the level of whole buildings or is it focused more on individual products or components? Does it deal with a specific topic or concern, like energy use, or does it cover a broad spectrum of sustainability issues? Is the tool quantitative or does it include subjective or qualitative elements? Too often these distinctions are ignored and comparisons are made between tools that are intended for entirely different purposes. BEES and the Athena EIE are complementary tools, intended to meet different needs at different stages in the project delivery process, not competitive tools between which one must choose.3. A Closer Look at BEES and the EIE
BEES and the EIE provide LCA information to aid material selection during the design process, but for different purposes and in different ways. It's useful to take a closer look at the two tools, what they do and how they do it, and at the underlying intent or purpose of each in the design and delivery process.3.1 BEES
An especially valuable feature of BEES is its ability to provide users with direct comparisons between environmental performance and life cycle costs, thereby making trade-offs explicit. The direct economic versus environmental comparison is just one of many ways in which a user can view side-by-side comparative results for different products. Results can also be viewed by life stage and by environmental flow (e.g., flows of substances such as ammonia, hydrogen chloride, and sulfur oxides that contribute to acid rain) for a list of 12 performance measures.
BEES uses importance weights to combine environmental and economic performance measures in a single performance score, although the user can select a “no weighting” option. If weighting is selected, the user first decides how to weight environmental versus economic performance (e.g., 50/50 or 40/60), and then selects from among four alternative weighting systems for the environmental performance measures. The four alternatives include a user-defined option and equal weighting as well as two systems developed by scientific panels. Users can also change the default discount rate used for calculating the present value of life cycle costs.
BEES 3.0 includes approximately 200 building products or variations on products, including about 80 brand-specific products. For example, in the ‘slab on grade' product category, there are 10 generic product variations and six brand-specific variations. In the case of floor coverings, there are 17 distinct generic products and 18 brand-specific products. The generic data covers the most representative production technology or an aggregated result based on U.S. average technology for the relevant industry. Brand-specific data was provided through the participation of a number of manufacturers in the 'BEES Please' data program.
BEES is available for download free of charge from www.bfrl.nist.gov/oae/software/bees.html .3.2 Athena EIE
As note earlier, the Environmental Impact Estimator was developed by the Athena Institute to make it possible for architects, engineers and researchers to assess the environmental implications of industrial, institutional, office, and residential building designs at an early stage in the project delivery process. By working at a whole building level, it captures the systems implications of product selections related to a building's structure and envelope.
The tool is regionalized — it currently covers eight specific regions for Canada, three for the U.S., and a U.S. average — and allows users to take account of the embodied effects of material maintenance and replacement over an assumed building life, distinguishing between owner-occupied and rental facilities where relevant. The building life is selected by the user and can be varied to assess relative durability effects. The Estimator also allows embodied effects of materials production and use to be compared to and merged with estimates of operating energy use that have been separately developed using energy 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 the Institute's life cycle inventory databases for about 100 generic structural and envelope materials, the Estimator simulates over 1,000 different assembly combinations and is capable of modeling the structure and envelope systems for about 95% of the building stock in North America . Results are provided for detailed environmental flows from and to nature as well as in the form of six summary measures. The use can make side-by-side comparisons of as many as five alternative designs, for any one or all of the summary measures. The comparisons can be among variations on a base case, or can include completely different projects. Similar projects with different floor areas can be compared on a unit floor area basis.
For more information, please visit the Institute's web site at www.athenaSMI.ca
4. Picking the Right Tool
To understand how BEES and the EIE fit in a complementary suite of sustainable building tools, and where each is best used, we have to focus on the kinds of questions asked and the information needed at different stages in the project delivery process. We also have to be conscious of the difficulty of maintaining functional equivalence when making building material comparisons.
4.1 Maintaining Functional Equivalence
In LCA-based comparisons , we use the term ‘functional equivalence' when referring to the problem of ensuring that two or more products provide the same level of service. Ensuring functional equivalence in product comparisons is not as easily accomplished in building applications as might be supposed. The problem is that the choice of one product may lead to, or even require, the choice of other products. For example:
• the choice of 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 floor covering.
In all of these examples, product comparisons should take account of other material-use implications of the alternatives. In other words, comparisons should be made in a building systems context rather than on a simple product-to-product basis. Even though two products may appear to be equivalent in terms of specific criteria like load bearing capacity, they may not be at all equivalent in the sense of true functional equivalence.
In a similar vein, we should be cautious to take account of all the components that may be required during building construction to make use of a product. Mortar and rebar go hand in hand with concrete blocks, just as fasteners, tape and drywall compound are integral to the use of gypsum wallboard, and nails are an essential component of a wood stud wall.
However, not all products pose a functional equivalence problem to the same degree. In general, product-to-product comparisons are more likely to be misleading when dealing with structure and envelope materials, where the systems context is key. As we move to interior finishes, fit- out products and furnishings, product-to-product comparisons are more realistic. For example, resilient or flexible floor coverings can readily be compared to each other as long as we take account of installation materials, cleaning products, expected service life, and what happens at the end of a product's life. Even window systems, although part of the envelope, are typically delivered to a construction site as pre-assembled components that can be compared to each other in terms of thermal performance or other criteria, and without too much regard for broader systems implications.
In short, we can think in terms of a continuum from very systems-oriented products at the structural end of the scale, to more stand-alone products at the interior fit-out end. The task is to exercise caution and judgment about whether any given comparison is legitimate.
• Different Questions at Different Stages
Different tools are intended to address different types of questions at different stages in the design process, and that in turn has a bearing on the kind of data that is best for each tool. The EIE is intended for use at the conceptual design stage when significant environmental effects are often locked in by basic structure and envelope decisions. At that stage in the process, the designer makes critical and sometimes irreversible decisions and therefore has to have good information about the relative effects of materials, components or design alternatives at a generic level. Seldom is there concern at this stage about 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, brand-specific information becomes much more important at the specification and procurement stages of project delivery. Indeed, this kind of data is essential for product categories where there is high differentiation in environmental performance. BEES is already meeting that need in a number of product categories, floor coverings for example, and can be expected to continuously expand to meet the need in other categories.This should help make clear the complimentary nature of BEES and the EIE. These Level 1 and 2 tools serve critical needs at different stages in the project delivery process, and can serve as valuable inputs for Level 3 tools, such as LEED Ô .