METHODS

Tally facilitates the quantification of a Life Cycle Assessment of building materials for whole building analysis as well as comparative analyses of design options. The object of study may represent the complete architectural, structural, and finish systems of a building or a subset of those systems. It may be used to compare the relative contributions of building systems to environmental impacts and for comparative study of one or more reference buildings.

Functional Unit and Reference Flow

The functional unit of the study is the usable floor space of the building or buildings under study. The reference flow is the amount of material required to produce a building designed according to the given goal and scope of the assessment, over the full life of that building. For comparative studies and benchmarking, it is the responsibility of the modeler to ensure that reference buildings are functionally equivalent in terms of scope, size, and relevant performance. The expected life of the building is also set by the model author. The default life span of a building is 60 years.

System Boundaries and Delimitations

The analysis accounts for the full cradle-to-grave life cycle of the design options studied, including material manufacturing, maintenance and replacement, eventual end-of-life, and the materials and energy used across all life cycle stages. Optionally, the construction impacts and operational energy of the building can be included within the scope.

Architectural materials and assemblies include all materials required for the product’s manufacturing and use including hardware, sealants, adhesives, coatings, and finishing. The materials are included up to a 1% cut-off factor by mass with the exception of known materials that have high environmental impacts at low levels. In these cases, a 1% cut-off was implemented by impact.

Manufacturing [EN 15804 A1-A3] includes processes wherever possible. This includes raw material extraction and processing, intermediate transportation, and final manufacturing and assembly. The manufacturing scope is listed for each entry, detailing any specific inclusions or exclusions that fall outside of the cradle-to-gate scope. Infrastructure (buildings and machinery) required for the manufacturing and assembly of building materials are not included and are considered outside the scope of assessment.

Transportation [EN 15804 A4] between the manufacturer and building site is included separately and can be modified by the practitioner. Transportation at the product’s end-of-life is excluded from this study.

Construction [EN 15804 A4] is based on the anticipated or measured energy and water consumed during the construction of the building.

Maintenance and replacement [EN 15804 B2-B5] encompasses the replacement of materials in accordance with the expected service life. This includes the end-of-life treatment of the existing products [EN 15804 C2-C4], transportation to site, and cradle-to-gate manufacturing of the replacement products. The service life is specified separately for each product.

Operational energy treatment [EN 15804 B6] is based on the anticipated energy consumed at the building site over the lifetime of the building. Each associated dataset includes relevant upstream impacts associated with extraction of energy resources (such as coal or crude oil), including refining, combustion, transmission, losses, and other associated factors.

End-of-life treatment [EN 15804 C2-C4] is based on average US construction and demolition waste treatment methods and rates. This includes the relevant material collection rates for recycling, processing requirements for recycled materials, incineration rates, and landfilling rates. Along with processing requirements, the recycling of materials is modeled using an avoided burden approach, where the burden of primary material production is allocated to the subsequent life cycle based on the quantity of recovered secondary material. Incineration of materials includes credit for average US energy recovery rates. The impacts associated with landfilling are based on average material properties, such as plastic waste, biodegradable waste, or inert material. Specific end-of-life scenarios are detailed for each entry.

Data Source and Quality

Tally utilizes a custom-designed LCA database developed in collaboration between KT Innovations and thinkstep (formerly PE International). It combines material attributes, assembly details, and engineering and architectural specifications with environmental impact data. LCA modeling was conducted in GaBi 6 using GaBi databases and in accordance with GaBi database and modeling principles.

Geography and date: The data used are intended to represent the United States region and the year 2013. Where representative data were unavailable, proxy data were used. The datasets used, their geographic region, and year of reference are listed for each entry. An effort was made to choose proxy datasets that are technologically consistent with the relevant entry.

Uncertainty: Uncertainty in results can stem from both the data used and the application of the data. Data quality is judged by its precision (measured, calculated, or estimated), completeness (e.g., unreported emissions), consistency (degree of uniformity of the methodology applied on a study serving as a data source), and representativeness (geographical, temporal, and technological).

The LCI data sets from the GaBi LCI databases are widely distributed and used with the GaBi 6 Software. The datasets have been used in LCA models worldwide in industrial and scientific applications, both as internal and critically reviewed and published studies. In the process of providing these datasets, they are cross-checked with other databases and values from industry and science. The application of datasets to model each entry is based on technological, geographical, and temporal representativeness. The uncertainty introduced by the use of proxy data is reduced by using technologically, geographically, and/or temporally similar data.

It is the responsibility of the user to apply the predefined material entries appropriately to the building under study. An effort should be made to utilize entries that are technologically similar to the material being modeled.

Tally methodology is consistent with LCA standards ISO 14040-14044.