Skip to content

Expert Tips

Calculating the Embodied Carbon of Different Structural Systems

A review of life cycle assessment (LCA) tools available to designers of U.S. commercial and multi-family projects, as well as carbon calculators and links to additional information on LCA tools and methodology.

It is useful to start with a brief background on the potential for wood buildings to have a lighter carbon footprint than buildings made with other materials. Wood reduces a building’s carbon footprint in two ways. It stores carbon that was originally absorbed by the trees while growing, keeping it out of the atmosphere for the lifetime of the building—longer if the wood is reclaimed and re-used. Meanwhile, the regenerating forest continues the natural cycle of carbon absorption.

The other aspect is that wood products typically require less embodied energy to manufacture than other building materials, and most of that comes from renewable biomass (e.g., bark and other mill residues) instead of fossil fuels. Substituting wood for fossil fuel-intensive materials is a way to avoid greenhouse gas (GHG) emissions. Life cycle assessment (LCA) studies consistently show that buildings with wood structural systems have a lower embodied carbon footprint than buildings made with other materials.

With growing availability and code acceptance of mass timber products such as cross-laminated timber, there is great potential for larger and taller wood buildings to have a near-term environmental impact through carbon storage and lower embodied energy.

Life Cycle Assessment

Sustainable design is complex and integrated. One way to understand the interaction of factors involved in new construction, renovation, and retrofits is through LCA. LCA is defined in ISO-14040 (2006) as: “Compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product system throughout its life cycle” Using a cradle-to-grave analysis approach, LCA provides detailed information about the environmental impacts of a building’s operation as well as upstream environmental burdens associated with its materials and products, and their transportation and construction energy use. Whole Building LCA (WBLCA) covers all stages in the life cycle of a building and its components, from raw material extraction (cradle) and transportation; product manufacturing, transportation, building construction and operation; and eventual recycling or disposal (grave).

LCA Tools for US Multi-Family & Commercial Projects

LCA tools are intended to assist designers and owners in the early stages of a project when they’re making decisions aimed at reducing the environmental impacts of building systems. LCAs can be performed on individual systems, e.g., to compare structural systems or cladding systems, or a WBLCA can be utilized to compare entire building designs, including structural systems, mechanical systems, cladding systems, etc.

In the US, the two most common and robust WBLCA tools are the Athena Impact Estimator for Buildings, a stand-alone tool that uses Athena’s own highly regionalized database for the US and Canada, and Tally, a Revit software plug-in that relies on the international GaBi database. One-Click LCA is primarily used in Europe but expanding in the US. One-Click LCA is based on Environmental Product Declaration (EPD) data, which some experts believe is not well suited for LCAs due to inconsistencies between product categories. One-Click LCA is part of a suite of products that incorporates life-cycle costing and circular economy analysis.

WBLCA tools have the most sophisticated data sets and methodology for comparing building systems and, as such, can yield the best comparisons between wood and non-wood structural systems. They are also the tools most frequently utilized for green building credits/certifications. In general, a WBLCA considers the production of building materials, including raw material extraction, manufacturing and transportation, occupancy energy demand for an estimated service life, and end-of-life scenarios with a cradle-to-grave approach.

Athena and One-Click both offer software tools for preliminary estimations early in the pre-design and conceptual phases. While these early-phase tools may not be user-friendly for modification on some parameters (such as new building materials), they allow designers to quickly perform calculations to compare building systems early in the design process.

The table below summarizes the LCA tools described above along with three carbon calculators available to design professionals in the US. It is intended to help designers sort through the options available for LCA analysis and is not intended to be a complete comparison of the tools available.

Table summarizing LCA tools with three carbon calculators

(Click image for larger view)

Users are cautioned not to compare results between different LCA tools or even within different versions of the same tool. The Life Cycle Inventory (LCI) database and methodology are often different and continue to evolve as new research becomes available, and the field of WBLCA is not yet mature enough for easy characterization/comparison of tools. To accurately compare the tools against each another, an LCA expert would need to analyze the data, methodology, and uncertainties.

Before embarking on an LCA, it is useful to understand the LCI database and methodology utilized in the different software programs. Links to the software and methodology are provided at the bottom of this page. While there are limitations to idealized models in a WBLCA or LCA that will never perfectly represent real life conditions, designers can achieve usable results by selecting the most appropriate LCA tool, ensuring that the building is accurately modeled within that software, and engaging a sustainability consultant/LCA expert if/when needed.

There are also several international LCA tools available. However, before utilizing an international LCA tool for a US project, designers should verify that its US data is robust enough for the level of analysis desired, especially if the tool is being used to compare and select systems and products.

For further questions on LCA tools or assistance in finding an LCA expert to help analyze your wood building, contact WoodWorks’ Help Desk at help@woodworks.org.

Other Carbon Calculators

EC3:

The Embodied Carbon in Construction Calculator (EC3) is not an LCA tool for comparing structural systems. It is an EPD-based tool intended to compare building products within the same category based on their carbon dioxide (CO2) emissions. For example, it could be used to compare two insulation materials to identify the one with the lighter carbon footprint. A comparison of structural systems, such as wood framing to concrete or steel, requires a complete LCA.

While a beta version of the EC3 tool was launched November 2019, it has data limitations that don’t allow it to accurately evaluate wood products at this time.

WoodWorks Carbon Calculators:

The WoodWorks Carbon Estimator and Carbon Calculator estimate the total wood mass in a building and the associated carbon impacts. Carbon impacts refer to both the carbon stored in the wood building materials and the GHGs avoided by choosing wood instead of another more GHG-intensive, non-wood material.

The difference between the tools is that the Estimator is based on square footage and building type, while the Calculator is based on actual wood volumes and therefore offers a greater degree of accuracy. However, the results from both tools are estimates; they do not indicate a whole building or product-level carbon footprint or global warming potential and are not intended to replace an in-depth LCA. LCA studies and tools that are in compliance with ASTM E2921, ISO 14025, ISO 14040/44, ISO/TS 14067, ISO 21930 and ISO 21931-1 provide more complete results, and are therefore more useful for decision-making purposes.

LCA Tools and Methodology

Tags

Related Resources