Preservationists and residents alike have spoken at length in support of the recently threatened Sanford-Bristol House (c. 1790), of Milford, Connecticut. An architecturally unique and irreplaceable historic home, it’s also a highly visible element of Milford’s River Park Historic District. These considerations alone justify the effort to save this unusual homestead.
However, there’s another compelling reason to save the Sanford-Bristol House, as well as other, similarly threatened historic homes, that’s not often raised in our public discourse, and that’s the environmental impact of demolishing these homes and replacing them with new construction.
Here’s a brief summary of the scientific underpinnings of my argument: Back in the early 1970s, a team at the University of Illinois investigated the energy typically used in construction . They focused on the concept of embodied energy, which is the total energy required to create something new from raw materials, plus any additional energy expended in further transforming the new object’s state. Their research culminated in a published inventory of embodied energies for typical construction materials and methods.
What’s so powerful about the idea of embodied energy is it enables one to assign a measurable energy cost to the current or projected future state of any manufactured product. And since embodied energy can never be recovered, this cost also includes the energy lost from destroying that product and replacing it with a new one. Furthermore, how a product’s actually made makes no difference (in principle) as far as its quantity of embodied energy is concerned; the same amount of energy is required to form a given object, whether made by machine, or human hand.
But where manufacturing processes differ are in their relative degrees of environmental sustainability. Human labor, for example, is reasonably sustainable, as long as adequate supplies of food and oxygen are available. By comparison, fossil fuels, which power most of our machinery today, are a one-shot deal; although highly energy-dense, they’re limited in quantity, and irreplaceable. Furthermore, extracting and refining fossil fuels damages the environment, while burning them produces CO2, methane, nitrous oxide, and other green house gases.
The ACHP and The Greenest Building
Now, as you can imagine, buildings possess tremendous amounts of nonrecoverable, embodied energy. In fact, the ongoing creation, augmentation, and replacement of all that embodied energy in the built environment of the United States currently consumes about 37% of our annual, non-renewable, fossil fuel-based energy production , with a direct consequence being a proportional amount of environmental harm.
So, from the standpoint of environmental sustainability, an important question to ask is: What’s the net energy expenditure of rehabilitating an old building, versus demolishing and replacing it with a comparable, new structure? We can quantify this question by recasting it in terms of embodied energy: What’s the net energy expenditure of conserving and possibly augmenting an existing store of embodied energy, versus disposing of it and creating a new store of comparable size?
In the late 1970s, the Advisory Council on Historic Preservation set out to answer these questions by developing a computational framework to estimate and compare the relative energy costs of rehabilitation versus demolition-replacement for historic buildings . Their published framework consisted of several mathematical models that leveraged the University of Illinois’ inventory of embodied energy data.
The ACHP publication included a case study evaluating three diverse historic buildings using these energy costing models. For all three, it was found that rehabilitation incurred a much lower net energy expenditure than demolition and replacement, the lower cost of rehabilitation being directly attributable to conserving the large quantities of embodied energy carried by each of these existing buildings .
Finally, in more recent times, the May T. Watts Appreciation Society created several online embodied energy and demolition energy calculators, based on the ACHP models. They also created construction and demolition waste calculators, based on published EPA data on non-hazardous waste generation , . These calculators, and much background information on them, can be found at The Greenest Building .org , .
The Sanford-Bristol House
As a real-world example, let’s see what results the embodied energy, demolition energy, and construction and demolition waste calculators return for the Sanford-Bristol House.
Energy Cost of Demolition
According to Zillow.com, the Sanford-Bristol House has a gross area of 2388 square feet. Supplying this value and the basic house type to the embodied energy and demolition energy calculators gives us the following:
The Sanford-Bristol House stores about 1,671,600 MBTUs (thousands of British Thermal Units) of embodied energy. That’s the energy equivalent of about 288 barrels of crude oil, since a barrel of crude oil yields about 5.8 million BTUs. This is the total amount of non-recoverable, embodied energy that will be lost (or more accurately, made forever inaccessible/unavailable/unusable), should the Sanford-Bristol House be demolished.
The demolition energy (the energy required to destroy a structure and dispose of the waste material) for the Sanford-Bristol House is considerably less: 7402.8 MBTU, or about .4% of the home’s embodied energy. So, the total energy cost of demolishing and removing the Sanford-Bristol House is about 1,679,003 MBTU, or just one more barrel of oil over the cost of the home’s embodied energy.
Replacement Energy Cost, Final Energy Cost, and Carbon Debt
Mr. William Farrell’s application to the Milford Building Department to build a new home at 111-113 North Street specifies a single family home of 1900 square feet. To determine the energy required to build this new home, we enter the gross square footage and building type into the embodied energy calculator:
So, the energy required to build the new home is about 1,330,000 MBTU.
However, assessing the final energy impact of Mr. Farrell’s proposal using the ACHP model requires summing all three energy costs, since the embodied energy of the Sanford-Bristol House will be lost during its demolition:
1671600 MBTU + 7402.8 MBTU + 1330000 MBTU = 3009002 MBTU.
Thus, the final energy cost for the complete teardown, haul-away, and replacement of the Sanford-Bristol House is approximately 3,009,002 MBTU, which is equivalent to about 518 barrels of crude oil.
Now, I should point out that the embodied energy of the Sanford-Bristol House represents an environmental debt (mostly resource extraction and depletion) that’s already incurred, and furthermore, had largely been incurred during the days of manual and animal labor. But the energy driving demolition and new construction today will be obtained primarily by burning fossil fuels, and these processes will incur a significant, additional carbon debt that’s proportional to the amount of energy expended.
That required energy is about 7402.8 MBTU + 1330000 MBTU = 1337403 MBTU, which is equivalent to approximately 231 barrels of crude oil, which, in turn, is equivalent to about 218,257 pounds of CO2 . This is the same quantity of CO2 that would be released by an average U.S. single family home over a time span of about 83 years .
While this estimate of carbon debt is just a broad approximation, it provides a reasonably good idea of the magnitude of environmental impact of the current proposal for the Sanford-Bristol House, something which otherwise would not be at all obvious.
Demolition and New Construction Waste
Building demolition and construction waste currently accounts for about 40% of all solid waste generated annually in the United States . Minimizing its production, therefore, is another key environmental justification for building conservation and preservation.
How much solid waste would be generated by demolishing and replacing the Sanford-Bristol House? The Greenest Building .org’s construction and demolition (C&D) waste calculator estimates combined demolition and new construction waste, and demolition waste alone, based on building type and gross floor area. If you want to find the waste generated by new construction only, simply take the difference of these two values.
Here are the C&D waste calculator panels, supplied with design values for both the Sanford-Bristol House and its proposed replacement home:
Demolishing the Sanford-Bristol House will produce about 133 tons of waste, which must be dealt with (either reclaimed, recycled, or carted off to a landfill), while building the replacement home is estimated to produce about 4.2 tons of waste. Recall that debris removal energy costs are factored into the demolition energy estimates, but this doesn’t include post-removal energy costs for recycling.
A third panel of the C&D calculator estimates the equivalent amount of trash produced by a single U.S. citizen in years:
So, demolishing and replacing the Sanford-Bristol House will produce a quantity of solid waste that’s approximately equivalent to what an average U.S. citizen would produce in about 163 years. Again, this is yet another metric illustrating a potential environmental impact of the Sanford-Bristol House proposal that’s otherwise not immediately obvious.
Rehabilitation Energy Cost
If you’ve managed to stick with my (admittedly dry and clinical) analysis up to this point, you’re probably beginning to suspect that rehabilitating the Sanford-Bristol House might have considerably less of an environmental impact than demolishing it. And you’d be right about that. So let’s see what the ACHP model has to say about the energy costs of rehabilitation.
The Greenest Building .org doesn’t offer a rehabilitation energy calculator, but we can easily compute this estimate using the embodied energy calculator and the ACHP concept model. The ACHP concept model defines rehabilitation energy as the embodied energy of the existing building, multiplied by the percentage of the building requiring restoration. Scientifically, this amounts to augmenting the embodied energy store of the existing building by that percentage, but otherwise conserving the embodied energy already present.
Now, coming up with a reasonable estimate of that percentage is essential for an accurate calculation. Doing so in this case would require a comprehensive inspection of the Sanford-Bristol House itself, something I’m not in a position to do. But in lieu of that, I can still calculate rehabilitation energies for arbitrary lower and upper bounds of that percentage, and use them to make useful comparisons.
Proponents of replacing the Sanford-Bristol House have publicly claimed that only a small percentage of the home can actually be saved. “Ten percent” is one estimate that seems to keep coming up in the various news reports. Personally, I don’t buy this. But let’s assume, for the moment, that it’s true. This means 90% of the existing Sanford-Bristol House needs to be rehabilitated (which, by the way, doesn’t necessarily mean replacing board-for-board and post-for-post, as some people might claim).
According to the ACHP model, the rehabilitation energy would then be estimated as:
.9 x 1671600 MBTU = 1504440 MBTU
which is about 1/2 of the total teardown and replacement energy cost of 3002340 MBTU that we’d calculated earlier, and clearly 1/2 the associated carbon debt, as well.
This estimate shows, then, that rehabilitating the Sanford-Bristol House, even to an extreme degree, would result in far less environmental degradation than tearing it down and replacing it, even with a 20% smaller replacement home.
Rehabilitation Construction Waste
Finally, let’s consider the quantity of construction waste that would be generated by such an extreme rehabilitation of the Sanford-Bristol House. The C&D waste calculator doesn’t include a panel for rehabilitation. But we can still get the answer we want simply by using the percentage of the original square footage that needs to be rehabilitated as the replacement square footage:
Subtracting the original demolition waste estimate out of this result gives us an estimate for the solid waste generated by rehabilitating the home:
137.60 tons – 132.89 tons = 4.71 tons
This is just slightly more than the construction waste generated by building the new replacement home, but two orders of magnitude less than the total construction and demolition waste that would be produced by a full teardown. So, here we have yet one more comparative measure of environmental impact that supports rehabilitation over demolition and replacement. And once again, without this detailed analysis, none of this would’ve been obvious.
Environmental Impact: Summary and Comparison
The following spreadsheet summarizes and compares the main results of the preceding analysis of the Sanford-Bristol House:
Embodied Energies of Early Historic Buildings
It should be pointed out that, while conceptually correct, the ACHP computational framework, and the online calculators based on it, provide rather broad estimates of embodied energies and related costs. One concern about this model is how accurately it represents the embodied energies of very early historic structures, such as eighteenth century timber-framed or masonry homes.
In an APT Bulletin article published in 2005 , architect Mike Jackson spoke to this concern. He’d suggested that the embodied energies of early historic buildings are most likely underestimated by these models, given their generally over-built construction, and use of greater amounts of materials, than for similar structures of more modern vintage.
If Jackson is correct on this point (and I believe he is), then the case for conserving early historic buildings is even stronger than what the ACHP framework suggests. A good empirical investigation of the embodied energies of the earliest materials and methods would go a long way toward verifying what seems to be a credible assessment by Jackson.
Those determined to destroy historic homes and replace them with new housing often rely on whole litanies of platitudinous claims to justify their proposed actions. Their goal, of course, is to gain public approval by playing on popular misconceptions about the nature and operation of historic homes, as well as our deeply ingrained cultural bias that acquiring something new is always preferable to perpetuating something old.
Often, they’ll claim that replacing the older home with a new one will provide some great benefit to the surrounding community, either in terms of enhanced neighborhood value, or improved health and safety. And, in fact, if you peruse the various news articles and accounts of public hearings on the Sanford-Bristol House, you’ll find this particular claim central to Mr. Farrell’s argument, and one that was readily embraced by the Milford Historic District Commission.
What I’ve provided here, however, is a reasoned argument, based on long-established and well-understood scientific models and data, that the public is quite likely being asked to accept the scenario that incurs the greatest degree of long-term, environmental degradation. It’s unfortunate, of course, that this possibility only becomes apparent following a lengthy analysis, and that this analysis most likely will still prove unconvincing to those more comfortable debating in platitudes.
 Hannon, Stein, Segal, and Serber, Energy Use For Building Construction, Energy Research Group, Center for Advanced Computation, University of Illinois at Urbana-Champaign, February, 1977.
 Carroon, Sustainable Preservation: Greening Existing Buildings, Wiley, November, 2010, pp. 5-6.
 U.S. Advisory Council on Historic Preservation, Assessing the Energy Conservation Benefits of Historic Preservation: Methods and Examples, January, 1979.
 Ibid, pp. 57-91.
 U.S. Environmental Protection Agency, C & D Waste.
 U.S. Environmental Protection Agency, Municipal Solid Waste.
 May T. Watts Appreciation Society, The Greenest Building .org.
 May T. Watts Appreciation Society, The Greenest Building is the One Already Built, November, 2007.
 U. S. Environmental Protection Agency, Clean Energy Resources.
 U.S. Environmental Protection Agency, Clean Energy Calculations and References.
 Jackson, Embodied Energy and Historic Preservation: A Needed Reassessment, APT Bulletin Vol. 36, No. 5., 2005, pp. 47-52.
 Alter, Embodied Energy and Green Building: Does it matter?, TreeHugger.com, January, 2012.