When planning a new school, decision makers want to assure the best and most economically appropriate choices are being made. Reusing an existing facility is often an important option to consider. If an existing building is educationally sound, and code and accessibility are appropriate, renovating can reduce costs and preserve important community historical resources. But that decision also may have important environmental impacts that should be fully understood and included in any consideration.
As we all work to reduce our carbon footprint and the associated effects of global warming, we must go beyond increasing a building’s energy efficiency and minimizing fossil fuel use. Construction itself, including the manufacturing, mining, transportation, and ultimately the maintenance and disposal of building materials, also emits greenhouse gases. This category of emission is referred to as embodied carbon and accounts for 13% of overall greenhouse gas emissions.
In some cases, renovating rather than building new can reduce the amount of embodied carbon used on a project. Understanding embodied carbon impacts when considering whether to build new or renovate should be a key component of any school design project. As a design progresses, the same type of analysis also can be used to help understand which materials to select to further reduce a building’s embodied carbon.
Life Cycle Assessment
Such an analysis would, ideally, consist of a complete Life Cycle Assessment (LCA) that considers all building material and construction impact—from initial gathering and transporting of raw materials through manufacturing, installation, potential future recycling, and reuse throughout a building’s 60-year life expectancy. The industry is not yet able to completely and accurately measure that. Researchers do not have a full understanding of every material’s embodied carbon, or its true impact on critical issues like smog formation, ozone depletion, and depletion of non-renewable energy sources.
However, there is significant data on the embodied carbon of many materials, and there are more limited LCA analyses that go a long way toward understanding construction environmental impacts. This understanding enables designers and builders to determine the best choices for materials within a building. About 23% of total global emissions used in the built environment come from concrete, steel, and aluminum; the use of concrete makes up almost half of that.
A recently completed project to update and expand Bristol County Agricultural High School’s campus in Dighton, Massachusetts presented a unique opportunity to evaluate two buildings of comparable program and scale—one renovated and one new. Using software that quantifies the environmental impact of building materials, architects analyzed and compared the renovation of Gilbert Hall—an existing 72,000-square-foot academic building—with the new Center for Science and the Environment, a 73,500-sqiuare-foot academic building. This analysis helped quantify the different amounts of embodied carbon when comparing renovation and new construction. It also helped determine which materials contributed the most to the embodied carbon for each building, enabling planners to make the best material selection to minimize embodied carbon.
The LCA considered the embodied carbon impacts associated with the extraction, manufacturing, and transportation of materials used on both buildings. There was little information on the procurement or installation of materials in the original existing building, so that was not included in the comparison. Nor can the analysis quantify future reuse and recycling, so that wasn’t considered on the building analysis either.
The existing building, Gilbert Hall, was constructed in 1935 with three additions over time, resulting in many different structural systems. The existing exterior walls were a variety of uninsulated masonry and plaster and generally were in excellent condition. The design upgraded building performance by adding insulation to the interior of all walls and roofs. The appearance of the exterior was unchanged except for added partial stone veneer for durability. All windows and curtainwalls were replaced. The interior of Gilbert Hall was completely removed, apart from the structure. Ultimately, 69% of the building—primarily foundations, structure, exterior walls, roof, and floor construction—remained.
Analysis for the Center for Science and the Environment helped confirm and guide material selection. For instance, the design minimized finish materials by incorporating exposed floors and ceilings; that reduced the overall quantity of materials. Steel with a high recycled content was used to minimize the use of raw materials. The design team focused on simplifying the footprint to reduce concrete foundations. Ultimately the exterior aesthetic reflected the school’s historical existing context, using stone, brick, and metal.
The LCA comparing major building elements showed that for new construction, the structure, primarily concrete and steel, contributes most to the total embodied carbon. In the renovation, the majority of embodied carbon comes from the envelope.
The goal for both buildings was to eliminate waste and optimize efficiency. The reduced quantity of new materials required in an existing building versus a new building can, in many cases, contribute to a major reduction in a building’s embodied carbon—hence the inherent value typically in deciding to reuse existing buildings. Focusing on the LCA data for Gilbert Hall and the Center for Science and the Environment and comparing them with each other enabled the design team to understand and review the impacts of new materials required to complete the projects.
Both were below the Carbon Leadership Forum’s benchmark for school construction, an organization that tracks and researches embodied carbon.Gilbert Hall used 28% less embodied carbon in new materials than those used to construct the new Center for Science and the Environment. This means 744 metric tons of carbon emissions were avoided, while updating a significant piece of the school’s historical identity. This is equivalent to 18.1 acres of U.S. forests preserved from conversion to cropland in one year. The choice to renovate was easy for this project and provided important information for analysis on future design projects.
Major contributors to embodied carbon in both reports were concrete and metal. Concrete accounted for 25% of the total embodied carbon at the Center for Science and the Environment (CSE) and 4.2% at Gilbert Hall. Metal, including structural steel, aluminum, metal framing, roof and floor decking, accounted for 41% of the total embodied carbon in the CSE and 84% in Gilbert Hall.
This shows that the less concrete used in a project, the more other materials will become major embodied carbon contributors. Although it’s difficult to eliminate steel, other metals, and concrete from our buildings, schools and universities must use them as efficiently as possible to reduce environmental impact.
In many cases, renovation is the most sustainable option, but educational space requirements, codes, accessibility issues, specific material requirements, or demolition requirements can easily drive up a renovation project’s embodied carbon. So undertaking a LCA analysis is essential early in the design process.
Although an LCA is not a perfect measurement, it can guide schools and universities through a sustainable building design process by helping with deciding whether renovate or build and by weighing the embodied carbon impact of material selection. In combination with fossil-fuel-free systems, minimizing embodied carbon will help reduce the impact of the built environment on the natural environment.
It is important to remember that decisions regarding sustainability cannot be made in a vacuum. In addition to environmental impacts, planners must consider social and economic impacts of all decisions and projects to be truly sustainable.
Suni Dillard, AIA, LEED AP BD+C is a Senior Associate and Sustainability Leader at HMFH Architects, a 50-person architecture firm in Cambridge, Massachusetts, focused on educational facilities. Suni works on a range of K-12 education projects, that incorporate environmentally responsible design principles. She can be reached at [email protected].