Overview

The building sector is being called upon to help fight climate change by achieving ambitious reduction targets for greenhouse gas emissions while at the same time incorporating other “green” considerations. Life Cycle Assessment (LCA) – which allows the impartial comparison of building designs based on measures such as global warming potential – is an essential part of this effort and, thanks to the Athena EcoCalculator, is now more accessible than ever before to mainstream design professionals.

The EcoCalculator offers architects, engineers and others access to instant LCA results for hundreds of common building assemblies. The results embedded in the EcoCalculator are based on detailed assessments completed with the Athena Impact Estimator for Buildings, which in turn uses Athena’s own widely-acclaimed datasets and data from the US Life Cycle Inventory Database, www.nrel.gov/lci

Developed by the Athena Institute in association with the University of Minnesota and Morrison Hershfield Consulting Engineers, the tool was commissioned by the Green Building Initiative™ (GBI) for use with the Green Globes™ environmental assessment and rating system. Because of its value as an indicator of climate change impacts, the GBI supported the team’s creation of a generic version for use by the entire sustainable design community. This variant, the Athena EcoCalculator, is available free of charge, in two versions: EcoCalculator for Commercial Assemblies and the new EcoCalculator for Residential Assemblies.

Choose your Version

The Residential version has been developed to allow assessment of single family residential buildings, whether detached, semi–detached, or row houses. The Commercial version is suitable for industrial, institutional or office designs.

The EcoCalculator is regionalized; after selecting either the Commercial or Residential version, the user selects the city or climatic region reflecting the building’s location. The following North American cities are currently available: Atlanta, Calgary, Halifax, Los Angeles, Minneapolis, Montreal, New York City, Orlando, Ottawa, Pittsburgh, Quebec City, Seattle, Toronto, Vancouver, and Winnipeg. Alternatively, users can select a standardized USA Zone 3 or Zone 6. Other Southwest and Central regions will be added in the future.

In the EcoCalculator for Commercial Assemblies, users can also choose between a low– and high–rise version, depending on the building under consideration.

Using the EcoCalculator for Assemblies

The EcoCalculator can be used for new construction projects, retrofits and major renovations, either to compare specific assemblies or to assess all of the assemblies in a structure.

The first step is to select an assembly sheet from one of the following categories:

• Foundations and Footings
• Columns and Beams
• Intermediate Floors
• Exterior Walls
• Windows
• Interior Walls
• Roofs

The number of assemblies in each category varies widely depending on the possible combinations of layers and materials. Within the exterior wall category, for example, there are nine basic wall types, seven cladding types, three sheathing types, four insulation types and two interior finish options. The number of assemblies for exterior walls represents all viable combinations of these options.

Assemblies are assessed in terms of a range of performance measures:

• Fossil Fuel Consumption
• Global Warming Potential
• Acidification Potential
• Human Health Respiratory Effects Potential
• Eutrophication potential
• Ozone depletion potential
• Smog potential

To develop results, the user indicates the square footage represented by selected assemblies. Users can evaluate multiple assembly types within a category (e.g., exterior walls), in which case their impact measurements will be combined to arrive at a total environmental impact for that category.

Design results are available in tabular form and show real time changes as the inputs are adjusted by the user. This allows different assembly options to be considered in light of their environmental impacts and provides the information necessary to make informed, scientifically–based choices.

Ensuring Fair Life Cycle Comparisons

The Athena EcoCalculator for Assemblies is able to generate instant LCA results because each preset assembly has already undergone a lengthy assessment using the Athena Impact Estimator for Buildings.

The results take into account:

• Resource extraction and processing
• Product manufacturing
• On–site construction of assemblies
• All related transportation
• Maintenance and replacement cycles over an assumed building service life
• Structural system demolition and transportation to landfill

Operating energy effects can be included in whole building LCA using the Impact Estimator, but are not included in the EcoCalculator. Where the tool is used as part of a green building rating system, these effects are covered elsewhere.

To ensure fair comparisons between assemblies, certain assumptions were made.
Results are presented on a per unit area basis (e.g., per square foot), but the underlying Impact Estimator analyses were done on a whole building basis and actually took into account much larger quantities, for example, 1,000 linear feet of wall of a defined height with an assumed window–to–wall ratio. Installation for all assemblies was assumed to utilize components and loadings typical for central areas of the United States, with the exception of Vancouver, Seattle and Los Angeles, where seismic corrections are applied to the structural calculations. It was assumed that all assemblies would be used in “owner occupied office buildings” (in the Commercial version) or “single family residences” (in the Residential version) with a 60-year lifespan; building type and ownership assumptions affect the maintenance and repair/replacement schedules of relevant building envelope materials (e.g., roofing membranes, claddings and window systems).

Other specific assumptions covered factors such as:

• concrete strength and flyash content;
• gypsum board type and thickness with latex paint;
• live load for all intermediate floors, columns and beams, and roofs;
• bay sizes;
• column heights;
• external wall thicknesses depending on construction system;
• stud size/strength and spacing; and
• sheathing and decking materials.