Recently, I’d conducted a formal study of the gross environmental impact of demolishing the Sanford-Bristol House (c. 1790) of Milford, Connecticut, and replacing it with a smaller, replica home. What follows here is a brief synopsis of my findings. A link to the full study, which in turn links to all sources cited here, is provided at the end of this post.
The term “environmental impact” is defined here as a combination of 1) wasting energy already embodied by existing construction, 2) expending energy for new construction, along with its resulting carbon debt, and 3) solid waste generation. My analysis is based on well-known planning models and empirical construction data published by the U.S. Advisory Council on Historic Preservation (ACHP), the Energy Research Group of the University of Illinois’ Center for Advanced Computation, The Greenest Building .org, and the U.S. Environmental Protection Agency.
The table below summarizes and compares my results for two specific scenarios: 1) An extreme rehabilitation of 90% of the Sanford-Bristol House, and 2) demolition and removal of the Sanford-Bristol House, followed by construction of a new home that’s 80% of the original footprint. Note that my assessment of “90% rehabilitation” is a hypothetical, worst-case estimate that I’ve arbitrarily chosen just to make a comparison. The home most likely requires nowhere near this degree of rehabilitation, but a more realistic estimate would require direct inspection of the home, something I’m not in a position to do. Also note that the term “rehabilitation”, as defined by the ACHP models, and used here, refers to the systematic repair and restoration of an existing structure, and does not imply a one-for-one replacement of a building’s original components:
What the above comparison reveals is that even an extreme rehabilitation of the Sanford-Bristol House, based on a hypothetical, worst-case assumption of 90% of the home having to be rehabilitated and restored, would still incur only about 1/2 the energy loss and carbon impact of a complete demolition and replacement, and generate only about 4% of the solid waste of a complete demolition and replacement.
It should be noted that the ACHP’s concept model of embodied energy, which was the one used in this study, produces relatively course-grained estimates of energy loss and costs, based on building type and gross square footage. It’s perfectly suitable, however, for historic preservation planning purposes, and has been used by the ACHP in that capacity for many years. Two additional, more finely-grained models, whose calculations require lengthy inspections of building details and components (again, something not practical in this particular situation), have also been published by the ACHP.
My complete report, containing my assumptions, step-by-step calculations, and references to all published information sources, may be found at:
A complete archive of all Sanford-Bristol House articles posted here may be found at:
20 September 2013