Environmental Impact of Demolition-Replacement: Sanford-Bristol House Case Study

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.

Image of the Sanford-Bristol House (c. 1789-90).

The Sanford-Bristol House (c. 1789-90). From “History of Milford, Connecticut: 1639-1939″.

Embodied Energy

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 [1]. 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 [2], 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 [3]. 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 [4].

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 [5], [6]. These calculators, and much background information on them, can be found at The Greenest Building .org [7], [8].

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:

Embodied energy and demolition energy calculator panes, supplied with design values for the Sanford-Bristol House.

Embodied energy and demolition energy calculator panels, supplied with design values for the Sanford-Bristol House.

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:

Approximate energy expenditure to build a slightly small replacement of the Sanford-Bristol House.

Approximate energy expenditure to build a slightly smaller replacement of the Sanford-Bristol House.

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 [9]. 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 [10].

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 [2]. 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:

Estimated construction and demolition waste for the Sanford-Bristol House teardown and replacement.

Estimated construction and demolition waste for the Sanford-Bristol House teardown and replacement.

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:

Trash production per person equivalent of the construction and demo waste estimates for the Sanford-Bristol House.

Trash production per individual equivalent of the construction and demo waste estimates for the Sanford-Bristol House.

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:

Construction and demolition waste estimate for rehabilitating 90% of the Sanford-Bristol House.

First step in estimating the construction waste of rehabilitating 90% of the Sanford-Bristol House.

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:

Sanford-Bristol House: Comparison of environmental metrics for rehabilitation, versus demolition-replacement (based on ACHP models and The Greenest Building .org calculators).

Sanford-Bristol House: Comparison of environmental metrics for rehabilitation, versus demolition-replacement (based on ACHP models and The Greenest Building .org calculators).

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 [11], 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.

Epilogue

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.

#ThisPlaceMatters

References

[1] 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.

[2] Carroon, Sustainable Preservation: Greening Existing Buildings, Wiley, November, 2010, pp. 5-6.

[3] U.S. Advisory Council on Historic Preservation, Assessing the Energy Conservation Benefits of Historic Preservation: Methods and Examples, January, 1979.

[4] Ibid, pp. 57-91.

[5] U.S. Environmental Protection Agency, C & D Waste.

[6] U.S. Environmental Protection Agency, Municipal Solid Waste.

[7] May T. Watts Appreciation Society, The Greenest Building .org.

[8] May T. Watts Appreciation Society, The Greenest Building is the One Already Built, November, 2007.

[9] U. S. Environmental Protection Agency, Clean Energy Resources.

[10] U.S. Environmental Protection Agency, Clean Energy Calculations and References.

[11] Jackson, Embodied Energy and Historic Preservation: A Needed Reassessment, APT Bulletin Vol. 36, No. 5., 2005, pp. 47-52.

[12] Alter, Embodied Energy and Green Building: Does it matter?, TreeHugger.com, January, 2012.

About John Poole

My interests include historic homes, architectural preservation and restoration, improving the energy performance of old houses, and traditional timber frames.
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18 Responses to Environmental Impact of Demolition-Replacement: Sanford-Bristol House Case Study

  1. That is a very compelling argument, both for saving the house AND for taking a higher ed math class.

  2. Sean @ SLS says:

    Nice piece & job John at explaining the numbers & how they are arrived at. The only one I can see as being off is the rehabilitation waste as that varies on what the rehabilitation entails. For example, stripping lathe & plaster off all the walls would produce that amount of waste if not more (of course that really isn’t rehabilitation, more of a gut job…)
    Fingers crossed that the place is saved

    • John Poole says:

      Don’t necessarily disagree with you on that one, bud. That number does seem a bit low. It’d be nice if data from real-world rehabs could be collected and used to confirm these calculations, but each collection process would probably add quite a bit of overhead and not be cost-effective for most professionals to participate in (unless maybe there was research grant money backing it up). And thanks, regarding the place. There’s only about one more month remaining before the demo delay runs out.

  3. Thank you John for continuing to build the case against this pending atrocity…excellent points made, you have once more.

  4. fascinating. translation = dang yo!

  5. Richard Platt says:

    Thanks very much, John. Trouble is, those who should read this probably won’t, or they would consider it irrelevant. I had this happen to me a couple of years ago when I tried to make a similar case before a Board of Aldermen committee hearing. I was ruled out of order!

    • John Poole says:

      Hi Richard,

      Thanks very much for commenting!

      Yes, I totally agree with you that those who most need to read this sort of stuff will usually avoid it. And your encounter with the Board of Aldermen was truly unfortunate, and their reaction, in my opinion, was totally uncalled for.

      But the bottom line here is that historic preservation and environmental sustainability, as disciplines, are currently in the midst of a non-stoppable process of unification: Preservation is now acknowledged as a key enabler and working method of sustainability, while preservationists themselves are recognizing the need for using only sustainable materials and processes in their restoration and rehabilitation activities.

      So, anyone deliberately resisting getting on board with this cutting-edge thinking is eventually going to find themselves “left in the dust”, so to speak, as far as historic preservation, restoration, and planning are concerned.

      Of course, there are indeed many who’d prefer to remain behind, as your unfortunate aldermanic encounter would seem to suggest! ;-)

      ~ John

  6. Paul Saunier says:

    That is a nice analysis John. Also I like your coining of the phrase “aldermanic encounter” in your reply to Mr. Platt.

    • John Poole says:

      Thanks very much, Paul!

      I got the adjective “aldermanic” a long time ago from Monty Python, in a skit where John Cleese goes into the post office, demanding a license for his pet halibut.

      The mayor and aldermen later walk in and hand him an official exemption for a pet fish license. The narrator (sounding like he’s describing a football play), refers to the aldermen as being “…magnificently resplendent in their aldermanic hose”, which I found uproariously funny, so it always stuck with me.

      You can find it on YouTube: http://www.youtube.com/watch?v=nmyHup4TpkU. Forward to around 4:20.

      ~ John

  7. Bill Smith says:

    John, this is a great piece! Sorry for not keeping up, I think everyone just turned their phones on after labor day.

    One thing that jumped out at me is the value vs cost part here. The equivalent embodied energy at 288 barrels of oil costs, today, a bit over $30,800. But what would need to be replaced is the value of the original energy investment plus a reasonable compounding figure to arrive at the present value. That house has been serving as a savings account for that energy since it was built.

    If we invested $30,800 today and got 5% annual return in 50 years that would be $353,195.91. Without doing more research than I have time for today I couldn’t tell you the present value of the Sanford-Bristol home embodied energy but we can’t value it in terms of today’s costs (BTW, I know you didn’t :-}).

    When you add the embodied energy value to the psychological cost of losing an important tie to the past the only logical value you can put on the house is priceless.

    • John Poole says:

      Hi Bill,

      You make a very valid point regarding the differentiation of cost and value.

      When I’d first published this article, I’d likewise calculated the cost associated with the crude oil energy equivalence, for which I’d used $110 per barrel (the going average price that morning, according to Bloomberg), and came up with an amount very close to yours.

      However, I’d decided not to include that in the original article, because I felt these dollar costs were only transitory, and also might’ve confused my argument about the nature of embodied energy (which is hardly transitory).

      But your separating cost and value is truly insightful, and I think it would be fantastic if you’d consider publishing a more detailed assessment based on accumulated value over time, perhaps either here, as another guest post, or on your own blog, in which case, I’ll publicize and link to it from here.

      I’d also had a similar idea that a very, very old house should accumulate embodied energy “credits” based on how long it’s been extant, and its continued expected life time following any needed rehabilitation, versus the energy requirements of a new replacement house and its own expected life time.

      For example, if a new house is expected to survive for 50 years, an extant 250 year old house of similar size is worth about five times the new home in terms of embodied energy, because its long existence has (at least conceptually) obviated the need for a succession of five homes, each of which are equivalent to the modern replacement in terms of embodied energy. It’s a fuzzy notion, but I think you see where I’m going with this, and your idea of accumulated value over time might actually be what I’m trying to conceptualize with this.

      ~ John

  8. Bill Smith says:

    Drat! You’ve found my weakness John; a good challenge.

    I’ll take this on, but as we discussed elsewhere I’ve got a ton of stuff happening now. Let me consider a couple of approaches and angles. I think there are probably several valid ways to look at this, I’m going to toss this into my think box somewhere in my head for a few days and see where it goes.

    None of the traditional financial instruments are perfect analogies. The key is finding a realistic way to consider the value that can relate to something that is widely understood.

    One problem is going to be assigning a value to the intangible value existing buildings carry. That should probably be a second topic, but there must be a cross tie there somewhere.

    OK, the think box seems to be getting underway. I have a couple of road trips early next week, prime cogitating time.

  9. Juliana Inman says:

    As preservationists, we should take over City Hall. I mean it!

    When preservationists run for office and get elected, they are in a position to appoint the design review boards, historical commissions, and planning commissions; strengthen ordinances; and provide final approvals and denials of projects such as this when they are appealed.

    The buck stops with the local elected leaders. They will be responsible to voters for this proposed demolition. John, have you considered running for office?

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