The Preservation Green Lab at the National Trust for Historic Preservation has recently published their study The Greenest Building: Quantifying the Environmental Value of Building Reuse. Resolving many conflicted arguments, this study confirms that reusing and retrofitting existing buildings with an average level of energy performance almost always offers environmental savings over demolition and more energy-efficient new construction. The research provides the most comprehensive analysis to date of the potential environmental impact reductions associated with building reuse. The Preservation Green Lab utilizes Life Cycle Analysis (LCA) methodology to compare reuse and renovations with new construction over the course of a 75-year life span. Continue reading for more.
The study examines four environmental impact categories that include climate change, human health, ecosystem quality and resource depletion amongst these six building typologies: single-family home, multifamily building, commercial office, urban village mixed-use building, elementary school, and warehouse conversion. The typologies used are found in Portland, Phoenix, Chicago and Atlanta – the four U.S. cities selected to represent a different climate zone.
Key findings of the study reveal “savings from reuse are between 4 and 46 percent over new construction when comparing buildings with the same energy performance level”.
The reuse-based impact reductions may appear small when considering a single building, however the “absolute carbon-related impact reductions can be substantial when these results are scaled across the building stock of a city.”
For example, “if the city of Portland were to retrofit and reuse the single-family homes and commercial office buildings that it is otherwise likely to demolish over the next 10 years, the potential impact reduction would total approximately 231,000 metric tons of CO2 – approximately 15% of their county’s total CO2 reduction targets over the next decade.”
“This is a strategy that most policy-makers aren’t thinking about,” Patrice Frey, the director of sustainability for the National Trust for Historic Preservation, says. “Everyone wants a monument, a shiny new thing to put their name on, to make their mark. And I think some of it is just a cultural preference for new. We have a real estate industry that really – at least before the Great Recession – wasn’t particularly well attuned to dealing with existing buildings. The model was demolish the site, clear the site and build from scratch. That was the calculus they were used to.”
Also, building reuse with an average level of energy performance consistently offers immediate impact reductions, unlike nearly all energy-efficient new construction which can take 10 to 80 years to overcome the negative impacts created during the construction process. Check out the figure above.
Additionally, the study emphasizes the importance of material selection, as reuse benefits can be reduced greatly based on the type and quantity of materials selected for the project.
A summary of life cycle environmental impacts of building reuse found in this study is expressed as a percentage of new construction impacts, shown in the figure above. View this diagram and the complete study here.
“We’re not coming out and saying ‘all buildings have to be reused,’ and ‘all new construction is bad,’” Frey says. “What we’re advocating for is a shift in thinking, where at a minimum, we’re considering the environmental impacts associated with demolishing places before we tear them down and build something new.”
Check out some refurbished projects here on ArchDaily.