When we talk about the carbon footprint of our buildings, we concentrate on the operational carbon associated with their usage. Thanks to sophisticated energy modeling software, we are able to design, build, and run buildings with high-performance lighting and HVAC, and low-cost solar that are Zero-carbon and carbon-neutral in terms of operational emissions. But what about the embodied carbon in the materials we select? How do existing buildings fit in the carbon reduction dialouge?
(above) Typical LCA breakdown of GWP by energy use and
materials for a mid-sized office building
Historic preservation is inherently compatible with sustainability strategies because preservation is fundamentally about utilizing what we already have, and sustainability is about stewarding existing resources to avoid harm to future generations.
The Carbon Leadership Forum has conducted studies that show over the next 30 years, embodied carbon and operational carbon will be roughly equivalent. While operational carbon can be reduced over time through energy efficiency upgrades and renewables, embodied carbon is locked in place; we only get one opportunity to reduce embodied carbon. A typical LCA of a building will be calculated over 50-60 years, with certain materials such as windows and carpets being replaced during that timeframe. By applying LCA early, a project can evaluate the potential savings in carbon footprint from renovating a building compared to demolition and new construction. As Carl Elefante said, “The greenest building is the one that’s already built.’
Data from the U.S. Energy Information Agency suggests that buildings constructed before 1920 are actually more energy-efficient than buildings built at any time up until 2000, when new technologies and materials allowed for greater energy efficiency. In fact, in 1999, the General Services Administration (GSA) examined its building inventory and found that utility costs for historic buildings were 27 percent less than for more modern buildings.
Additionally, the District Department of Energy & Environment conducted a study, analyzing the energy performance data provided through its benchmarking regulations, and determined that there is no correlation between building age and performance.
Source: Sustainability and Historic Preservation: Options and Opportunities in DC - Building Innovation Hub
https://buildinginnovationhub.org/news/sustainability-and-historic-preservation-options-and-opportunities-in-dc/ (Accessed: 2021-12-23)
TIPS FOR SUSTAINABLE HISTORIC REHABILITATION PROJECTS:
There is a variety of retrofitting techniques that can be employed in historic structures to ensure reduced energy consumption, many of which are based on interior work not usually subject to oversight or review by jurisdictional commissions. The most common and effective include:
INSULATE unfinished areas first, such as attics and basements where historic fabric is less likely to be altered.
DIAGNOSE existing insulation and infiltration conditions with technologies such as blower tests, energy audits, and infrared thermographic inspections that can detect where improvements can be made.
EVALUATE existing heating, ventilation, and air conditioning (HVAC) systems to ensure they are functioning properly; replace them with higher efficiency units if needed. Maintain units properly for best performance. Supplement with low energy boosters like fans and shading devices.
Check with qualified preservation CONSULTANTS to see how renewable energy sources such as ground source heat pumps, solar panels, and wind turbines can be appropriately integrated into the project. Search for rebates for renewable energy sources.
EVALUATE existing lighting conditions and consult a lighting contractor if needed. Prioritize LED lighting use only when needed and install sensors that switch on and off with occupancy. Look for ways to improve interior natural daylighting.
REPAIR and MAINTAIN historic windows, light monitors and, skylights wherever possible. Add new skylights only on secondary facades or screened surfaces to bring in more natural light without losing historic integrity.
INSTALL low-flow plumbing fixtures and install aerators in existing fixtures to reduce water use by up to 40%. Provide rain barrels at downspouts to catch runoff and use water for landscape maintenance.
Source: https://www.dahp.wa.gov/sites/default/files/209SustainabilityStudy_ExecutiveSummary.pdf (Accessed: 2021-12-23)
Historic preservation is critical to achieving sustainability targets. It is possible to preserve the cultural history of existing buildings while reducing carbon emissions through adaptation, reuse, and efficiency improvements. Indeed, it is hard to achieve sustainability goals without taking into account existing structures, thus local governments and the real estate industry must rethink their approaches to the current built environment.