Until now, little has been known about the climate change reductions that might be offered by reusing and retrofitting existing buildings rather than demolishing and replacing them with new construction. This groundbreaking study concludes that building reuse almost always offers environmental savings over demolition and new construction. Moreover, it can take between 10 and 80 years for a new, energy-efficient building to overcome, through more efficient operations, the negative climate change impacts that were created during the construction process. However, care must be taken in the selection of construction materials in order to minimize environmental impacts; the benefits of reuse can be reduced or negated based on the type and quantity of materials selected for a reuse project.
This research provides the most comprehensive analysis to date of the potential environmental impact reductions associated with building reuse. Utilizing a Life Cycle Analysis (LCA) methodology, the study compares the relative environmental impacts of building reuse and renovation versus new construction over the course of a 75-year life span. LCA is an internationally recognized approach to evaluating the potential environmental and human health impacts associated with products and services throughout their respective life cycles.1 This study examines indicators within four environmental impact categories, reuse-based impact reductions may seem 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.4 When scaled up even further to capture the potential for carbon reductions in other parts of the country, particularly those with a higher rate of demolition, the potential for savings could be substantial. Given these potential savings, additional research and analysis are needed to help communities design and employ public-policy tools that will remove obstacles to building reuse.
It is often assumed that the CO2-reduction benefits gained by a new, energy efficient building outweigh any negative climate change impacts associated with the construction of that building. This study finds that it takes 10 to 80
years for a new building that is 30 percent more efficient than an average-per- forming existing building to overcome, through efficient operations, the nega- tive climate change impacts related to the construction process.5 As indicated in the following table, an exception also exists here for the warehouse-to-mul- tifamily building conversion. Upon analysis, this adaptive use scenario does not offer the carbon savings provided by other reuse scenarios.
Building reuse alone cannot fulfill the urgent task of reducing climate change emissions. The summary of results of this study, shown on the previous page, documents how reuse and retrofitting for energy efficiency, together, offer the most significant emissions reductions in the categories of climate change, human health, and resource impact. Certainly, the barriers to retrofits are numerous. However, a variety of organizations are presently working to address the obstacles to greening existing buildings. This study finds that reuse and retrofit are particularly impactful in areas in which coal is the dominant energy source and more extreme climate variations drive higher energy use.
Key findings from the analysis reveal that the reuse of empty homes could yield an initial savings of 35 tons of CO2 per property if the embodied energy related to new building materials and construction were eliminated.
The study finds that, when carbon emissions are looked at over time, it takes 35 to 50 years for a new, energy efficient home to recover through efficient opera- tions all of the carbon that was expended during the initial construction process.
Studies of embodied and operating energy are necessary steps in evaluating the environmental impacts of a building. However, other relevant factors – such as impacts to health, habitat, and air pollution – must also be considered. Con- sequently, the life cycle assessment (LCA) framework is a valuable tool towards understanding the importance of building energy consumption and related environmental concerns.
This section summarizes these results and highlights the following key findings for the scenarios analyzed in this study:
- building reuse almost always yields fewer environmental impacts than new construction when comparing buildings of similar size and
- reuse of buildings with an average level of energy performance consistently offers immediate climate change impact reductions compared to more energy efficient new
- materials matter: the quantity and type of materials used in a building renovation can reduce, or even negate, the benefits of reuse
Ultimately, a ‘year of carbon equivalency’ emerges – the point in a building’s lifetime at which the environmental impacts associated with new construction equal those associated with renovation. For the commercial building in Portland, for example, the ‘year of carbon equivalency’ occurs at year 42; it takes approximately 42 years for the efficient, new commercial building in Portland to overcome the climate change impacts that were expended during the construction process.
Significantly, even if it is assumed that a new building will operate at 30-percent greater efficiency than an existing building, it can take between 10 and 80 years for a new, energy efficient building to overcome the climate change impacts that were created during construction.
Materials Matter
In general, renovation projects that require many new materials – for example, an addition to an elementary school or the conversion of a warehouse to a residential or office use – offer less significant environmental benefits than scenarios in which the footprints or uses of the buildings remain unchanged. In the case of the warehouse-to-multifamily conversion scenario, the newly constructed building actually demonstrated fewer environmental impacts in the categories of ecosystem quality and human health.
Although warehouse conversions and school additions require more material inputs than other types of renovation projects, reusing these buildings is still more environmentally responsible – in terms of climate change and resource impacts – than building anew, particularly when these buildings are retrofitted to perform at advanced efficiency levels. Better tools are needed to aid designers in selecting materials with the least environmental impacts. Such resources would benefit new construction and renovation projects alike.
Every year, approximately 1 billion square feet of buildings are demolished and replaced with new construction in the United States.6 The Brookings Institution projects that some 82 billion square feet of existing space will be demolished and replaced between 2005 and 2030 – roughly one-quarter of today’s existing building stock.7 Yet, few studies to date have sought to examine the environmental impacts of razing old buildings and erecting new structures in their place. In particular, the climate change implications of demolition and new construction, as compared to building renovation and reuse, remain under-examined.
Although awareness about the need to reduce near-term climate change impacts is growing, a greater understanding of the potential environmental savings that can be offered by reusing existing buildings rather than developing new buildings is still needed. This study compares the environmental impacts of building demolition and new construction relative to building renovation and reuse. The study had three key objectives:
- To compute and compare the life-cycle environmental impacts of buildings undergoing rehabilitation to those generated by the demolition of existing buildings and their replacement with new construction;
- To determine which stage of a building’s life (i.e. materials production, construction, occupancy) contributes most significantly to its environmental impacts, when those impacts occur, and what drives those impacts; and
- To assess the influence of building typology, geography, energy performance, electricity-grid mix, and life span on environmental impacts throughout a building’s life
In examining these themes, the authors consider potential opportunities to reduce carbon emissions and other negative environmental impacts through building reuse and explore how differences in building type, climate, and energy-efficiency levels affect these opportunities.
This research is intended to serve as a resource for those who influence and shape the built environment, including policy makers, building owners, developers, architects, engineers, contractors, real estate professionals, and non-profit environmental, green building and preservation advocacy groups. To that end, the study identifies key environmental considerations and challenges related to new construction, retrofits and reuse. Findings from this study should be considered in light of the myriad realities that affect development decisions, such as building codes, zoning, financing, demographics, and design trends.
For those concerned with climate change and other environmental impacts, reusing an existing building and upgrading it to maximum efficiency is almost always the best option regardless of building type and climate. Most climate scientists agree that action in the immediate timeframe is crucial to stave off the worst impacts of climate change. Reusing existing buildings can offer an important means of avoiding unnecessary carbon outlays and help communities achieve their carbon reduction goals in the near term.
This report sets the stage for further research that could augment and refine the findings presented here. Study results are functions of the specific buildings chosen for each scenario and the particular type and quantity of materials used in construction and rehabilitation. Great care was taken to select scenarios that would be representative of typical building reuse or conversion projects. However, environmental impacts will differ for building conversions that use different types and amounts of materials. Others are encouraged to repeat this research using additional building case studies; replicating this analysis will enhance our collective understanding of the range of impact differences that can be expected between new construction and building reuse projects.
The study introduced important questions about how different assumptions related to energy efficiency affect key findings. In particular, further research is needed to clarify how impacts are altered if a new or existing building can be brought to a net-zero level using various technologies, including renewable energy.
About the Project team
This research was made possible by a generous grant from the Summit Foundation to the National Trust for Historic Preservation. The project was coordinated by the Preservation Green Lab, a programmatic office of the National Trust, which is dedicated to advancing research that explores the sustainability value of older and historic buildings and identifying policy solutions that help communities leverage their built assets. The project team includes Cascadia Green Building Council, Quantis LLC, Skanska, and Green Building Services.
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