[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.
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.
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].
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 interior 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.
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”
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.