Calculating Carbon Advantages in Adaptive Reuse Projects: The CARE Tool
Responsible Decision-Making
Designers are charged with making an incalculable number of decisions about their projects, and increasingly these include discussions about the carbon impacts of their designs. In making the best design decisions for responsible environmental impact, it often falls to the designer to guide the client towards the best path forward.
One of the questions that comes up quite often when a project is in its fledgling state is whether it would be best to design a completely new
building – either by demolishing an existing structure or clearing an undeveloped site– or adapting an existing building to fit the needs of the client’s program in a strategy known as adaptive reuse. Each method has drawbacks and advantages in various categories, but when it comes to narrowing down decisions in the environmental impact category, one of the looming concerns is how much carbon will be released into the atmosphere because of this project. Building construction and operation release a
significant amount of carbon into the atmosphere, and as the need for designers and decision-makers to be aware of their projects’ emissions has increased, the need to reduce how much carbon a project emits in the early stages of design has increased in kind1.
RALEIGH IRONWORKS
Calculating precise carbon metrics is a relatively new concept in the realm of building design, but some tools have become available to aid in this effort. The CARE (Carbon Avoided: Retrofit Estimator) Tool2 is one such tool. This online simulator uses information such as overall square footage (SF), glazing-to-wall ratio, and building use to calculate the carbon emissions of an adaptive reuse project compared to a brand-new building.
Embodied carbon emissions, which is carbon released through the actual construction of the building and the materials it uses
and discards; and operational carbon emissions, which is carbon released through the dayto-day use of the building, are both accounted for. The CARE Tool also allows designers and decision-makers to test various design options and methods to see what effects a design decision has on the carbon metrics of the project, such as:
» How much carbon will this project emit if it is built new?
» How much would be saved if it was built in an existing building?
» What adaptation methods would most effectively reduce the carbon emissions of this project?
This investigation analyzes a theoretical project example in the CARE Tool to learn what design decisions are associated with measurable impacts to carbon emissions. Testing various design configurations in the CARE Tool and similar simulators can give insight into the design factors that most significantly impact the building’s carbon emissions, and therefore help designers make informed decisions that maximize a project’s emission reduction potential.
PACIFIC BOX & CRATE
Project Setup: Existing Building
The CARE tool begins by establishing general information about the project: its location and climate information, electrical grid status, and the number of years over which the tool will model cumulative emissions. The theoretical project in this investigation is located in Charleston, South Carolina, postal code 29403. CARE is set to model emissions over the course of a fifteen-year period using the default climate and electrical grid information, which at the time of this analysis would end right around the 2040 mark.
Theoretical Project A (TPA) examines the advantages of adapting an office building for residential and retail use, which could become a common project example due to shifting retail markets. The second CARE tab asks users to input data for the existing building. TPA has a total area of 20,000 SF over the course of four floors above grade, with zero floors below grade. The structure is “steel and/or concrete,” and the window-to-wall ratio is 60%. The primary use is set to “Office,” and with no secondary use option the full floor area is given to the primary use. The use and operations of a building affect the carbon emission rate, and CARE reflects this nuance. This analysis uses the default energy use intensity (EUI) based on the information provided. Under these conditions, the existing building carbon emissions – operational emissions only, in this case, since no new construction means no embodied emissions – total 2,592 metric tons over the next fifteen years.
Project Setup: New Building
CARE’s fourth tab predicts the carbon emissions of a new building. If TPA were a new-build instead of an adaptively reused building – a 20,000 SF, four-story structure used for multifamily housing and retail – it might have a reduced operational emission level compared to the existing building as it stands, but the embodied emissions involved in demolishing an existing building and constructing a new one cannot be ignored. Since the building is intended for multiple uses, the square footage of the primary use and secondary use must be established; 16,000 SF go towards multifamily, and 4,000 SF go to the secondary use of retail store. Once more, the simulation uses the default EUI, only this time there is a target goal of 10% energy use reduction from its predecessor. All new electrical equipment is installed, and 7% of the electricity is produced by off-site renewables, since according to the U.S. Energy Information Administration, 7% of South Carolina energy is produced by renewables as of 20223. The new building would most likely be constructed of steel and/or concrete, so that setting remains the same as the original building, and for the sake of the simulation, selecting all the modifiers assumes best practices for new construction (low embodied emissions concrete, responsibly sourced timber, low embodied emissions envelope, and high-performance MEP systems). This new building would emit 1,380 metric tons of carbon over the course of fifteen years; however, it would also include embodied emissions of 762 metric tons cradle to grave due to the new construction. This puts the grand total at 2,142 metric tons of carbon over the fifteen-year period.
Project Setup: Adaptive Reuse Building
After establishing the original building characteristics and what a new building with the desired function and characteristics would be, the impact of design decisions for adapting the existing building becomes much clearer. Under CARE’s third tab, the building characteristics, use, and operational energy and emissions remain the same – 20,000 SF with no addition, four floors, a change of use with 16,000 SF of multifamily and 4,000 SF of retail, default EUI with a 10% target reduction in energy use, and 7% of energy by renewables. The Embodied Emissions section of the tool provides the most useful insight to what design decisions can have the most impact on the overall emission count. This section has five parts: Structural System Reuse; Envelope Reuse; Interior Reuse; Mechanical, Electrical, Plumbing Systems Reuse; and Modifiers, which have been used previously under the New Building tab. The reused building assessment tests are conducted with the modifiers turned on to assume best building practices, much like the new building assessment. Assuming there are no changes to any other parts of the building, changing each section by itself informs users what variable has the biggest impact on carbon emissions, and then bringing together all the design decisions made based on this knowledge and other relevant information gives a fair estimate of how the adaptively reused building emissions compare to what a new build’s emissions would be.
Structural Systems
Assuming the existing building does not change at all beyond its use and the previously established operational emissions parameters, TPA’s total emissions would be 1,380 metric tons of carbon in 15 years’ time. However, neglecting to take additional changes into account does not make for a feasible way to move the theoretical building forward – an office floor plan and a multifamily residential floor plan are not quite the same, after all – thus certain design factors must change, beginning with the structural system.
If TPA has a structural system that must be completely replaced, but no additional changes to the building are made, the cumulative carbon emissions increase from 1,380 metric tons to 1,958 metric tons, which is a delta 41.88%. If the structural system also needs a lateral upgrade due to its proximity to earthquake or hurricane zones, that number jumps even higher to 2,028 metric tons of carbon, a delta of 46.96%. Based on this test, the structural system clearly plays a significant role in the amount of embodied carbon a building contains. If TPA has a structural system that is fairly intact – maybe some reinforcing here and there, maybe a new stair or elevator is cut in the floor and needs to be framed around – leading to only a 25% removal of existing structure with lateral upgrades, the total emission count drop back down to 1,594 metric tons, which is only a 15.51% delta.
38TH STREET SCHOOL APARTMENTS
Envelope Reuse
Emissions due to building envelope changes can be examined after setting the structural changes back to zero. Once again, CARE reflects the worst-case scenario – while the building does not otherwise change, this test assumes all TPA’s exterior wall assemblies must be replaced and re-insulated, all the windows must be replaced, and the roof must be replaced and re-insulated. Despite its redundancy, checking “insulate walls” ensures the worst possible impact reflects in the test. The total carbon emissions increase from 1,380 metric tons to 1,444 metric tons, a delta of 4.6%. Compared to the impact of demolishing and replacing the entire structural system, this impact is rather light. When it comes to carbon emissions, however, every bit counts.
The most significant impact on this figure for TPA comes from replacing the windows; when the windows are all replaced but the walls and roof remain untouched, the emissions total 1,422 metric tons (change of 3.04%). If only the exterior walls are replaced, with no change to the existing windows or roof, the emissions total 1,400 metric tons, and if the roofing is replaced and everything else is left alone, the emissions come to 1,386 metric tons. Exterior wall replacement and roof replacement lead to changes of 1.45% and 0.43%, respectively. Unfortunately, replacing windows is one of the more common changes to an adaptively reused building envelope, since windows have gotten more efficient as their technology has developed and more efficient windows help reduce building energy use. While this design decision is extremely likely in an adaptive reuse project, the carbon emission impact is significantly lighter than other potential changes, so the benefits are more likely to outweigh the costs. If TPA ends up replacing all the existing windows, but the exterior walls receive only a “medium” level of repair (such as repairing all the building masonry) and a “minor” level of restoration of the roof, the total emissions for TPA would come to 1,424 metric tons. That is a 3.19% change from an untouched building envelope.
GRACE CHURCH ANDERSON CAMPUS
Interior Reuse
Changes to the building interior are particularly common – nearly inevitable – when a building gets a new use, such as with TPA. The CARE tool offers three degrees of interior alterations which can be used to varying degrees throughout the analyzed building design: restored/refurbished finishes, new finishes, and rebuilding/ reconfiguration. Once again assuming the worst-case scenario, if TPA needs to be completely gutted and rebuilt for its new use100% of the interior is reconfigured and rebuilt - the total emissions come to 1,476 metric tons of carbon, a delta of 6.96%. These metrics indicate that changes to the interior have a higher impact on embodied emissions than changes to the exterior – depending on the square footage of the building – but still significantly less impact than the structural changes. If TPA is in relatively good shape and some of the public areas of the building are salvageable with some new finishes but most of the building needs re-configuring for its new use – 5% restored finishes, 20% new finishes, and 75% rebuilt interiors, for instance – the carbon emissions would total 1,460 metric tons for a delta of 5.80%.
Mechanical, Electrical, Plumbing Systems Reuse
The ability to reuse the existing mechanical, electrical, and plumbing systems ties into how new the system is and how it can work with any changes made to the interior, so this parameter and the interior reuse parameter could be somewhat linked. If all systems in TPA need to be completely replaced, the total carbon emissions increase from 1,380 metric tons with no additional building changes to 1,504 metric tons, an increase of 8.99%. Medium changes to TPA’s system, such as replacing the system equipment but keeping the system distribution, only increases the emissions by 26 metric tons (1.88% increase). Minor repair and refurbishments increase emissions by only 6 metric tons (0.43% increase).
RALEIGH IRONWORKS
Conclusion
After examining the worst-case impact of each embodied emissions design factor and adjusting them for a more reasonable alteration to the existing building, the environmental advantage of adapting an existing building for TPA rather than building a new building becomes clear. If 25% of TPA’s structure has to be replaced and lateral support added, a medium level of exterior wall repair is called for, all windows replaced, minor repairs made to the roof, 75% of the interior reconfigured and rebuilt, 20% interior finishes replaced, 5% interior finishes restored, and a medium level of changes made to the MEP systems, the total carbon emissions come out to 1,746 metric tons in fifteen years. A new building would emit 2,412 metric tons of carbon in that same time period. With all the operational emissions metrics the same in this example, the difference between a new building and a reused building comes down to the savings in embodied emissions. The reused building emits 366 metric tons of carbon, cradle to grave, while the new building would emit 762 metric tons (see Figure 1), which is a savings of 396 metric tons of carbon.
In general, the building with the lowest embodied emissions is the one that changes the least. Knowing where you can make changes that have the least impact is an incredibly useful tool for making design decisions that tip the scale. If you have two designs in which one keeps most of the structure but changes the exterior envelope and interior significantly, and the one keeps the exterior envelope relatively intact but in turn most of the structure is lost, knowing how much impact saving an existing structural system has on the carbon emissions of a building becomes a significant variable in the ultimate fate of the project design. The cultural and financial impacts of reusing an existing building cannot go unnoted, either, and with the arsenal of knowledge that these environmental impact simulations and tests can provide, design remains thoughtful and purposeful.
KAYLEE JACOOB Practice Professional
Kaylee Jacoob is a Practice Professional in LS3P's Charleston office. A graduate of Ball State University with a Bachelor of Science in Architecture and a Minor in Historic Preservation, Kaylee joined LS3P in 2018 and has since been integral to growing our industrial, adaptive-reuse, and mixed-use portfolios. Kaylee is passionate about historic preservation; she is a member of the Historic Charleston Foundation and the Preservation Society of Charleston.
SOURCES
1. https://www.epa.gov/ghgemissions/overviewgreenhouse-gases
2. https://www.caretool.org/about/
3. https://www.eia.gov/state/analysis. php?sid=SC#:~:text=Solar%20energy%2C%20 hydropower%2C%20and%20biomass,state%20net%20 generation%20in%202022
FIGURE 1
