Deep Energy Retrofits and Historic Preservation: The Beginning of a New Dialogue

[Note: On April 3rd-4th, 2012, a spirited debate erupted in the Twittersphere on the topic of Deep Energy Retrofits, involving me (@BirminghamPoint), @EnergyCircle, @GreenCurmudgeon, @EnergyVanguard, @EESavers, @CLaumerGiddens, @SLSConstruction, @LeahThayer, and @PEGENG. My good buddy Sean Lintow Sr., of SLS Construction, realizing its importance, captured our debate in a post entitled "Deep Energy Retrofits -- The Conversation", on his Home Owners and Trades Resource Center blog, and kindly offered his blog as a platform for further discussion. To learn the detailed history of our debate, or view its current state, check out Sean's post. What follows here is a transcription of a lengthy comment I'd placed there. Since I have much to say about deep energy retrofits and their relationship to historic homes, this is the first of a series of articles on this topic that will appear in A Preservationist's Technical Notebook. Hopefully, my forthcoming articles will contribute to the overall continuity of this important dialogue.]

So what is a Deep Energy Retrofit, anyway?

A Deep Energy Retrofit (or DER) is a treatment applied to an existing building that significantly reduces the building’s annual energy consumption, much more so than would be realized by simpler energy conservation measures, such as routine air sealing and caulking, weatherstripping, upgrading to more efficient appliances, etc. A deep energy retrofit is most often (though perhaps not strictly necessarily) accomplished by making the building envelope as airtight as possible, and then super-insulating it. This reduces the size and/or energy consumption of the HVAC system the building requires. And it also usually necessitates the addition of mechanical ventilation (e.g., HRV/ERV) to maintain a positive fresh air flow through the living space.

Deep energy retrofits are not without their controversy, however. Often, retrofitting for deep energy reductions requires significant alterations to a building’s existing fabric. They’re expensive, and usually have long payback periods (100+ years is not an uncommonly quoted estimate for the payback period). Concerns also abound over the environmental and manufacturing-energy impacts of the materials involved. And there’s also a long running debate about whether deep energy retrofits are right for historic buildings, in terms of both cultural impact and the possibility of compromising the long-term durability of very old structures.

IR camera in use

Using thermal imaging to analyze the exterior of the Pierce House, c. 1683, Dorchester, Massachusetts.

What makes a home performance retrofit “deep”?

A simple criteria for defining a deep energy retrofit is a reduction of overall energy consumption by some percentage (for example, 30%, 50%, 70%, or 90%) over the energy consumption of a “comparable structure” built to current code. Sometimes, this percentage is expressed as a lower bound; sometimes, as a range. And some have suggested it be treated as a series of targets to be achieved over time. But it’s fair to say that, within the industry, there’s currently no strong consensus on just what this number ought to be. And regardless of the quantitative definition chosen, a deep energy retrofit must also satisfy all of the safety, durability, indoor air quality, ventilation, moisture control, etc., requirements that are normally considered a part of acceptable home performance, in general.

However, a key observation here is that, if we can agree on some simple, generic, baseline definition that doesn’t imply any particular implementation path, and an energy retrofit meets or beats that criteria, then that retrofit is a deep energy retrofit. It could’ve been accomplished using any of a number of different possible treatments, strategies, etc. But currently, the term “DER” is unfortunately conflated with the specific techniques and strategies being used in some of the more visible DER projects, or being advocated by the more well known DER practitioners. So, for many, the term “DER” is almost synonymous with super air-sealing and super-insulating, with the insulation step having very different implications, depending on whether it’s installed to the interior, or exterior, of the original wall sheathing.

Deep Energy Retrofits and Historic Homes

The term “Deep Energy Retrofit” freaks historic preservation people out. In part, because the publicized techniques of super-insulation, whether insulating-in, or insulating-out, ultimately impact some part of the pre-existing structure. And preservationists, of course, are obsessed with preserving as much of the original architecture and material of an historic structure as possible, because they believe there’s a certain intrinsic value to these old things that transcends the immediate concerns of the current moment.

But another concern of preservationists is the more subtle impact that energy retrofits might have on older structures, even if original fabric is not significantly impacted by the installation process. The reason for this is that the goals and techniques that went into building very old homes were quite different from the goals and techniques we employ today. A very old home, when viewed as a system, behaves very differently from a modern home. So there is considerable concern (and frankly, good reason for it) amongst preservationists about how the application of non-traditional treatments might affect traditional structures.

Roofing system

The roof system of the Pierce House. The historic record provided by exposed framing in very old structures often makes it impossible to even consider encapsulating such areas with spray foam insulation.

Now, interestingly enough, and by way of sheer coincidence, John Leeke of Historic Homeworks, author of the book “Save America’s Windows“, and a leader of the Windows Preservation Standards Collaborative (which is also focused on the energy performance of historic windows), happened to post a highly relevant comment on an earlier blog posting of mine, “A Pocket Manifesto for Historic Home Performance“, at about the same time the above mentioned Twitter debate was more or less in progress. Here’s part of what John said:

“…there are fundamental differences between traditional building technology and modern building technology. Whenever (with very very few exceptions) modern technology is introduced into an early building, sooner or later it generates a conflict that results in significant damage to the building.

This idea is based on my own 45 years of working on older buildings as a tradesman, contractor, owner and consultant. I did many things to many older and historic buildings during the 1970s ‘energy crunch’ that I,and in some cases, the building owners later regretted. These are important lessons to learn and pass along.

This is not to say that we should not do new things to old buildings, but we should be very careful and thoughtful about it, to realize what damage will be done and how significant it might become. I will admit that I am a ‘traditionalist’, but hope that I am not a ‘stuck in the mud’ traditionalist. You may want to check out my own Old-House Mechanics Manifesto.”

Now, John is not some genteel, delicate member of your local historical society who spends his afternoons sipping tea, attending lectures, and courting potential patrons. He’s the guy who’s been there and done all that, so to speak. His concerns (shared by a great many hands-on preservationist folks with equally impressive backgrounds) are based on a long history of things that have actually gone wrong, and not simply a collection of fearful hypotheticals dreamed up by cowering preservationist church mice. [Of course, many of you are aware of how famed building scientist Dr. Joseph Lstiburek also flaunts his long history of screwing things up back in the 1970s, and realizing now what he didn't know back then, in a manner that's very eerily similar to John's account].

Interior storm window

Aluminum interior storm windows are one approach to improving the thermal performance of historic windows. Durability concerns make it important to prevent moist interior air from entering the space between the two windows (and providing it with a means to escape, if it does enter).

So, this acknowledged concern by preservationists about retrofitting historic and very old homes for improved performance, is quite well-founded, and is driven by many past incidences of unforeseen, negative effects, caused by incongruous treatments. As a result of all this, many preservationists call for the use of “reversible”, or “re-treatable”, methods of energy retrofitting, that are blended with traditional building techniques, wherever possible. Not only do I support this, but I also strongly advocate the formulation of protocols for the post-retrofit monitoring of both energy-use and building health metrics, so that potential durability problems can be detected as early as possible.

Can Deep Energy Retrofits be consistent with Historic Preservation?

At one point in our Twitter conversation, I painted a scenario of super-insulation being applied in a manner that’s durable, reversible, and doesn’t destroy (much) historic material, as a form of super-insulating that wouldn’t be at odds with the goals of historic preservation. I’m first to admit, however,  that that illustration was decidedly unfair — it’s not anything that I think can realistically be achieved. At least, I don’t think it can be fully achieved.

But what I’d neglected to say on Twitter (though I was leading up to it, until I got tired and tuned out) is that performance retrofitting methods that do satisfy the requirements of durability and reversibility/re-treatability, and are based on techniques that are more in keeping with traditional building methods and materials, and satisfy the other requirements for home performance and deep energy efficiency, are indeed being researched, specified, and carefully put into use by dedicated practitioners working on historic properties.

The key point here is that, if treatments based on these proposed techniques can be shown to reduce the energy consumption of an older home within some (yet to be agreed upon) quantitative range defining a deep energy retrofit, then we will have achieved a deep energy retrofit using methods more appropriate for very old homes. The term “deep entry retrofit” might then, in time, come to connote these methods whenever it’s applied in the context of an historic building, and therefore be more likely to be embraced by preservationists. Several real projects attempting this are already yielding numbers approaching the low- to mid- range energy reduction percentages cited earlier (about 30%-50%). And at considerably less cost, and in a manner more consistent with traditional building techniques. In subsequent articles, I’ll describe a number of these ongoing projects.

Alexandra and keeping room fireplace

Alexandra standing next to an ancient atmospheric combustion appliance in the Pierce House keeping room.

Preservationists don’t hate Energy Efficiency

On final point: Preservationists are not opposed to energy efficiency, as is sometimes charged. Most preservationists these days readily acknowledge that home performance is now a critical part of preservation. Durability is what will keep an old building alive for a few more centuries. So are comfort and lowered operational costs, because these are among the things that will keep dedicated homeowners living in older homes.

But I believe that, at least within the context of historic and very old homes, preservationists also need to take ownership of this problem, and develop preservation-centric home performance treatments and strategies that are right for historic buildings. Preservationists need to become energy guys, rather than allowing non-preservationist energy guys, no matter how well intentioned, to take over the wheel and drive for them.


Here are links to all of the great blog posts associated with this discussion, more or less in the order in which they were published. As more related postings emerge, links will be added here.

Sean Lintow Sr, “Deep Energy Retrofits — The Conversation

John Nicholas,”Deep Energy Retrofits — A Twitter Conversation

Peter Troast, “What is a Deep Energy Retrofit? Experts at the NESEA Conference Respond

John Nicholas, “A Twitter Conversation — Moving Along, Part 2

Allison Bailes, “Historic Preservation and Deep Energy Retrofits — Natural Enemies?

Sean Lintow Sr, “Deep Energy Retrofits, Historical Properties, And The Conversation

Leah Thayer, “Controversy over Deep Energy Retrofits“, BPI Performance Matters Newsletter, April, 2012.

John Nicholas, “The Conversation Continues!

[ February 16th, 2013 ]

Old House Journal just published this article on the historically sensitive energy retrofit of the Lyman Estate being undertaken by Historic New England. Current measurements suggest that a 40-49% reduction in energy consumption over baseline has been achieved, to date.

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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17 Responses to Deep Energy Retrofits and Historic Preservation: The Beginning of a New Dialogue

  1. Pingback: Deep Energy Retrofit’s – The Conversation | The HTRC: Homeowner's & Trades Resource Center

  2. Glad to see the conversation continuing though I will have to say I hate the idea of a flat percentage being used especially one as low as 30%. I do have a question for you which was actually brought out in one of Peter’s tweets yesterday – this is just about historic homes…
    So what is the definition of a historic home – is it anything built before X &/or of particular historic significance (whether recent or in the past)
    Along those lines, does the age impact what DER methods in your mind would be acceptable?

    • John Poole says:

      Thanks, Sean.

      I totally agree with you that a flat percentage seems less than adequate, but it seems to be the predominant definition of deep energy retrofit that people throw around. In Peter Troast’s posting “What is a Deep Energy Retrofit?” (the one linked in your DER convo posting), six different experts provide nearly six different answers. The percent reductions they cite, respectively, are: 70-90, 75, 50, 50+, 50+, and 75-90 (the caveat attached to this last one being a claim that this won’t be achieved by a retrofit alone, but also requires extreme conservation and changes in habits, as well). But in any event, I agree that 30% seems oddly low, and I’m not quite sure why the author(s) of that Wikipedia page settled on that number.

      Perhaps one nice outcome of this little forum discussion of ours might be to come up with a single definition that we all agree to, even if it’s just amongst ourselves.

      Regarding the term “historic”, pinning it down to a single definition or criteria is likewise just as difficult as for DER. Certainly, any building on the National Registry of Historic Places, or listed by a State Historic Preservation Office, or listed as “historic” by a local historical commission, or situated in a designated historic neighborhood, would probably be qualified to be called historic, regardless of how old it actually is.

      Often, buildings are designated as historic based on factors other than age in years, such as if some one famous built it, or designed it, or lived there, or if it played a role in some historically significant event, or even if it just somehow instills a favorable sense of “place” or “continuity”. For example, both Frank Lloyd Wright’s “Falling Water” and the Walter Gropius House would undoubtedly be considered historic homes, even though both were only built in the 1930s.

      I’ve also seen the period 1870-1875 sometimes used as a line of demarcation between what is truly “historic” versus what might be considered “vintage” or just “very old”, but I’m not quite sure what’s so magic about that period. Perhaps it signifies the beginning of the period of modern industrialization that took place after the civil war. It was during this period that wire nails and stud framing started to come into use, as well as the beginning of the widespread use of fossil fuels. So that might be it. But still, all things are relative: In New England, this period is still relatively recent, but much farther west, it’s almost the beginning of time.

      So the short answer is, there really is no single, solid answer for what constitutes “historic”, just as there’s (currently) no single good answer for what constitutes a DER. It’s more like a final determination based on specific cases and taking multiple factors into account! :-)

  3. John,

    These ongoing contributions to the conversation are important. Thanks for pulling your comment out and letting it hold its own place.

    I put up another on my blog after reading your comment this morning.

    Thanks to Sean for keeping the ball rolling. I’m curious how Leah will be able to grab all this and connect the people and push the synergy of people working together.

  4. “Several real projects attempting this are already yielding numbers approaching the low- to mid- range energy reduction percentages cited earlier (about 30%-50%). And at considerably less cost, and in a manner more consistent with traditional building techniques.”

    I’m tempted to impose on you now for details . . . the answer to which would surely include of a proper definition of the word “traditional” — but alas I guess I will wait for future installments.

    Great introductory post John! Thanks!

    • John Poole says:

      Thanks very much, jb!

      “Traditional” meaning things like pointing foundation stones with lime mortar, instead of air-sealing with spray foam. (Who would’ve thunk it? :-) (Lime mortar is non-toxic, doesn’t off-gas, and further more, sequesters carbon dioxide). Another is the use of rock wool for insulation, which stands up to moisture and has a greater R-value than fiberglass. Traditional methods tend to cost more, because of the workmanship required in applying. But many feel that the total net cost to do this sort of retrofit is still far less than that of a conventional DER, which can be quite expensive.

      Don’t worry…this topic/debate has a long way to go, and there will much forthcoming detail. (At least from my end of things….).

      Have a good one, jb!

      - John

  5. cool! thank you for the details John and I can’t help but think that you were made for this discussion. looking forward to following. ~jb

  6. John –
    I’m wondering if you would allow us to rebroadcast this blog at our Antique Homes Facebook page.


  7. Pingback: Deep Energy Retrofits, Historical Properties, and the Conversation | The HTRC: Homeowner's & Trades Resource Center

  8. Overly aggressive energy conservation without increase in productivity, safety,, personal comfort and attention to usage of the service will inevitably fail. People will always find ways to circumvent unwanted or impractical restrictions. With historic venues, it would be throwing out the baby with the bath water, because careless or insensitive energy methods will hasten disintegration of the very cultural heritage meant to retain.

    • John Poole says:

      Thanks very much for your comment, Gersil.

      Your emphasis on usage and service is well taken, and I totally agree that an overly aggressive, “to the man with a hammer” style of energy retrofit, just for the sake of achieving high performance numbers, carries a high risk of compromising the very same structure it’s being claimed to improve.


  9. Pingback: Deep Energy Retrofit’s – The Conversation

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