Building consultancy BranchPattern released its second analysis in 2024, based on 2023 data from green building-certified assets from leading developers.
Construction is often blamed for a significant amount of greenhouse gas emissions — 40%, including indirect emissions. By understanding the processes, designers and builders should better identify sources of greenhouse gases that are embodied in the buildings. Global Warming Potential (GWP) is a measure of the radiative forcing impact of various green house gases (GHGs) over the course of 100 years. GHGs measure carbon dioxide (CO2), methane, fluorinated gases, nitrous oxide, among others.
The emphasis on embodied carbon is to avoid the intellectual bias of only thinking about the energy employed to operate a building. Better controlling that type of energy use is critical. But much of the GHGs involved with buildings are trapped in the materials, structures, subassemblies, and furnishings. It must look at the entire life cycle of the building and where the parts come from. They come into play through the extraction of raw materials, manufacturing, transportation, installation, maintenance, eventual deconstruction, and waste processing.
The 2019 Global Status Report for Buildings and Construction from the International Energy Agency determined that 28% of annual global emissions come from building operations, while 11% are emitted in the construction of buildings. Most embodied carbon occurs at the start of the project.
Construction of a 300,000-square-foot core and shell warehouse results in 6,000 MT of lifetime CO2e (CO2 equivalents). That’s the same as 1,571 gasoline-fueled cars driven for a year or the carbon sequestered by 7,706 acres of U.S. forests in one year.
The analysis was done on 94 projects in the study. That isn’t large enough to be statistically representative, but it’s significantly larger than the 26 projects in the first version. Most buildings in the study were smaller than 500,000 gross square footage. Larger projects showed greater variability in size. Buildings and trends will vary by geographic location. Construction in colder climates tends to require heavier framing to manage snow loads as well as increased insulation. Buildings in seismic zones have their own requirements due to earthquakes.
The shell sees a variety of types of tasks: site pavement (24%), miscellaneous site work (6%), foundation (4%), slab on grade (24%), exterior vertical enclosures (13%), roof construction (17%), structural frame (10%), and other (2%). The core comprises the following: concrete (46%), steel (22%), asphalt (7%), insulation (6%), and membrane (5%).
Of these, the highest impact materials include concrete, steel, asphalt, insulation, and the roof membrane. Combined, the five materials make up 84% of the embodied carbon impact.
There are five key methods for reducing concrete and steel emissions: cut cement content using lower-carbon alternatives, trim the volume of concrete, replace all steel with low-embodied carbon steel, optimize paving design, and use a measured approach to mass timber.