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Building Matters

Do Deep-Energy Retrofits Make Sense?

One design-build firm says no and instead favors modest building envelope upgrades, larger heat pump systems, and residential solar production

Conditioning an attic to house HVAC ducts and equipment is a common deep-energy retrofit strategy. Is it worth it?

Back in the late aughts, my design-build remodeling firm, Byggmeister, staked its reputation and identity on deep energy retrofits (DERs), a strategy for dramatically reducing energy use of existing homes by wrapping them in thick layers of “outsulation” and meticulously air-­sealing them. We’d been working at improving home-energy performance for decades, and we saw tremendous potential in this strategy to achieve deep reductions in the carbon emissions of existing homes.

We were wrong. We did our last DER in 2017, and now we routinely talk people out of them. In the intervening years, it seems that DERs have only become more popular, at least in concept, and Byggmeister is still widely known as a DER firm, which puts us in the awkward position of arguing against an approach we helped pioneer. How did we go from DER evangelists to skeptics?

Revisiting our approach

We first learned about DERs just as the enormity of the climate crisis was coming into focus. We had already been quantifying the impact of our work for a few years, measuring each project’s energy use before and after our upgrades. The results were underwhelming. On some projects, we were achieving modest energy savings of maybe 20% to 40%. On others, we were making no dent. On still others, we were making matters worse. We realized that if we were going to do our part to cut energy use and carbon emissions from existing buildings, we would have to change course.

The first change we made was deciding that we wouldn’t add on to a home without first exploring whether we could meet the client’s functional goals within the home’s existing footprint. Now, when we get an inquiry for an addition, we let homeowners know that it’s often more economical and environmental to reconfigure their existing space and put the money they would have spent on an addition toward improving performance. If the homeowner responds positively, we’ll move forward. Sometimes we even end up doing an addition. But we start from the premise that we can usually meet our clients’ needs without adding on, and now we do a lot fewer additions than we used to.

The second change we made was that we committed to improving energy performance on every project. Whereas before we would often allow a client’s interest to determine the energy scope, we began to conduct energy assessments of every home we worked on and recommend energy improvements as a matter of course. Now, if potential new clients don’t seem interested in saving energy, we know they aren’t a good fit for us.

While these were significant changes in our approach to remodeling, their impact seemed as though it might be too little, too late. That’s why the DER was initially so appealing.

Legislation charts a course

In 2008, Massachusetts passed two pieces of groundbreaking legislation. The Global Warming Solutions Act and The Green Communities Act committed the state to aggressive goals for reducing greenhouse-­gas emissions. Shortly thereafter, our electric utility, National Grid, announced a deep energy retrofit pilot program for single-family and small multifamily homes. National Grid’s program reimbursed eligible projects 75% of the cost up to a maximum incentive threshold. For single-family homes, the maximum ranged from $35,000 to $42,000 depending on the conditioned floor area. We jumped in with both feet.

Over the next few years we completed several DERs, aiming for the following prescriptive targets: R-10 basement floor, R-20 basement walls, R-40 above-grade walls, R-60 roof, R-5 windows, and air leakage of roughly 1 ACH50. Some of these were partial DERs in which we would focus on a part of the envelope, typically the roof. On all of our whole-house DERs, we typically upgraded mechanical equipment and installed solar PV.

The savings did not disappoint, with whole-building DERs achieving energy use reductions of 60% or more over baseline (we used actual utility-use data wherever possible to quantify savings; when we didn’t have this data, we relied on modeled usage). The homeowners were thrilled with their low utility bills and improved comfort. One bragged that he could comfortably walk around his home in his bare feet when it was 0°F outside.

Then just as interest in DERs was ramping up, we stopped doing them. We stopped for several reasons. The first was that Massachusetts ended the DER pilot program, and the utility money stopped flowing. At that point, the costs were too high. Homeowners who were initially very enthusiastic about reducing their energy use by 60%, 70%, or 80% were much less enthusiastic when we told them how much it could cost. Even for a house with relatively simple geometry, outsulating can be two to three times more expensive than insulating (for new construction the costs of going from code-level performance to high performance may be marginal, but this is never the case for retrofits). Of course, outsulation comes with improved performance, but without generous incentives we had a very hard time selling it.

Carbon takes on importance

At first we found the difficulty in selling the idea of exterior insulation disappointing, and hoped we could figure out a way to bring down the costs. Then we learned about embodied carbon, or the upfront carbon emitted during the initial stages of a material’s lifecycle. Of all insulation materials, foam plastics have the highest upfront emissions. Foam had been our go-to insulation material, which means that we had been burdening our DERs—projects whose primary purpose was to save energy and carbon—with extraordinary carbon debts. We briefly looked into doing DERs with carbon-storing materials such as wood fiberboard, but our estimates indicated that wood fiberboard DERs would be even more expensive than using foam.

In the meantime, improvements in heat-pump technology opened a new decarbonization pathway that didn’t rely on extreme envelope measures. When we first started doing DERs, only homes with very low heating loads could heat exclusively with heat pumps. Now that we have heat pumps that perform well in very low temperatures, we no longer need to wrap a home in thick layers of insulation and drop the air leakage to less than 1 ACH50 to go all-electric.

Improving efficiency is necessary but insufficient to address the climate crisis. We also need to electrify our energy use and decarbonize our energy supply. And we must do these things simultaneously in a very compressed timeframe if we hope to avoid the worst effects of climate change. We believe this means that we should stop doing DERs and instead couple modest upgrades in efficiency with heat pumps and solar (when appropriate).

Modest upgrades, larger heat pump

While it’s true that a very low-energy home can get by with a much smaller and simpler heat-pump system than a thermally average home can, we have found that for most homes the cost/benefit analysis favors more modest efficiency improvements and larger heat-pump systems over DERs and smaller heat-pumps systems.

Over the past several years we have converted dozens of thermally average homes to heat pumps and have done partial conversions on many more. On the low end, energy use and carbon emissions are 15% to 20% less than pre­-project usage and emissions. On the high end, energy use and carbon emissions are 60% to 70% less.

Probably our most successful modest retrofit to date has been of a 1930s colonial. Except for minimal attic-floor insulation, this house was mostly uninsulated before we did our work. It also had an ancient boiler and water heater. We insulated the basement walls with 2 in. of closed-cell spray foam, dense-packed the wall cavities with cellulose, and insulated the underside of the roof with 3 in. of closed-cell spray foam followed by 7 in. of cellulose. With these measures, we reduced air leakage by 60%.

We also installed a ducted heat-pump system, a heat-pump water heater, and an induction cooktop. Operating carbon emissions went down by 70%, and because we minimized our use of foam and relied on cellulose wherever possible, the carbon storage of the cellulose offset the emissions of the foam, meaning that the envelope measures were carbon neutral.

Of course, most of our projects don’t achieve this level of savings because most homes start out more efficient than this one. But with this approach, I believe that we’ve been able to achieve greater reductions on many more homes than if we had continued our DERs.

Weighing the benefits

That’s not to say that modest retrofits coupled with heat-pump conversions are without their challenges. In our experience, a heat-pump system often costs more to install than a new gas heating system. We’ve also learned the hard way that heat-pump systems must be designed and installed by knowledgeable and skilled tradespeople to perform well. There are too many poorly designed and installed heat pumps. And too many are put into homes that haven’t had modest efficiency upgrades, resulting in comfort complaints and increased utility costs. We’re also concerned about refrigerant leaks, having suffered a couple on our projects. And if widespread electrification isn’t coupled with load reduction, the potential for strain on the electric grid during peak heating days is also a significant concern.

Even with all these challenges, we think our approach is the best way for us to reduce household carbon emissions. We could be wrong, just as we think we were wrong about DERs. All we can do is stay abreast of current science and technology and be willing to change course if—or rather, when—we learn a better way.


Rachel White is CEO of Byggmeister, a design-build remodeling firm in Newton, Mass. This article originally appeared in Fine Homebuilding magazine, issue 314.



  1. 1910duplex | | #1

    What kind of exterior did the colonial have? Our duplex also was uninsulated when we bought, and we did a flash-and-batt at roofline, but we have plank sheathing with 110-year-old stucco on one side and plaster on the other, and have been told that's a dangerous mix with wall insulation.

    We have done ducted heat pump upstairs that we now use for cooling but have been afraid to get away from our radiators, thinking we will be too cold.

    1. brendan_kavanagh | | #23

      Hi I worked with Rachel on these projects and the colonial had wood clapboard. If you’ve got heat pumps and a fossil fuel system we typically recommend just setting the heat pump a degree or so and setting your radiator tstat back a degree or so. This will allow the heat pumps to run as primary and for the radiators to pick up any slack, if there is any.

  2. Expert Member

    What an articulate and thoughtful article! Good luck to them.

  3. paul_wiedefeld | | #3

    Bravo! A pragmatic approach. DERs really cannot pay for themselves and aren’t the low carbon option either. They need to sell themselves on comfort or be heavily subsidized to gain traction.

  4. frankcrawford | | #4

    I would call both what Byggmeister were and are now doing Deep Energy Retrofits, just the parameters have evolved towards Net Zero on site Energy and Electrification. The path each home takes to achieve that goal will vary by home and climate. The key is that it starts with an energy assessment and a plan to reach the goal. The steps can be broken up into multiple years but each step is fully planned out so it does not impede future steps. Adding the exterior continuous insulation (in the form of dense packed cellulose in a Larsen truss cavity) when the cladding needs replacement at end of life is much more cost and carbon effective.
    We still need many more DER's to meet our climate goals, we just need to ensure the DER are designed to achieve the climate goals, which at this point is green house gas emission reductions.

  5. maine_tyler | | #5

    The upfront carbon emissions of foam is no different on a DER than new construction. Cellulose does not 'offset' other embodied carbon emissions either.

    I'm not sure I understand how 'more energy' is now saved by doing less extensive energy upgrades? Do you mean to say more energy in total because you have time to tackle more projects?

    The upfront carbon of residential solar also meeds to be accounted for, and the fact that it does not (necessarily) reduce peak grid demand as well. Rooftop may not be worth it at all by traditional economic measures.

    What we need to move forward is better economic accounting of externalities, across the board. It's hard to 'prescribe' anything.

    1. brendan_kavanagh | | #24

      Hi I ran the analysis on these projects and what rachel and I meant by offset is that the carbon storage attributes commonly associated with cellulose offset the emissions associated with the minimal amounts of spray foam that we used in this project based on our calculations using the BEAM calculator.

      We feel that we can both do more of these moderate projects and that more of them will happen with electrification than if we or our clients held the line at a full outsulation DER standard.

      Your points on solar and other factors are definitely something we struggle with but given the climate issues I think it’s important we avoid analysis paralysis and still move forward with the work we find most effective, while keeping an eye out for new information or tools than can help us refine that direction every now and then.

  6. spraggins | | #6

    Bravo for the new approach to well thought out energy improvements. Problem is, too many times they are not well thought out. I have seen to many times, well intentioned energy improvements lead to devastating damage to older homes. This has sort of lead to the myth that homes need to breathe, when in reality they need to dry or stay dry. The wrong insulation in the wrong place can easily lead to hidden condensation points that are not found until too late.
    The one nice thing about the full DER method is that the envelope is fully considered from inside to outside. This same consideration is desperately needed for partial energy improvements, it’s just the industry does not have good methods for doing the necessary exploratory surgeries on houses with proper planning from those finding.

    1. brendan_kavanagh | | #25

      We have found the same thing, however it’s still very possible to make critical mistakes trying to do a traditional DER especially when you try to keep costs to your clients as low as possible. In doing any of this work it’s important the practitioners are careful and knowledgeable, which is impossible to achieve universally in any industry.

  7. proposterosa | | #7

    Interesting article. A few questions

    - How do you calculate the embodied CO2e for various DER materials?
    - What lifespan do you use to calculate the expected lifecycle reductions of a DER?
    - Do you consider the load shifting potential of more extensive envelope improvements?

    That last one has become apparent to me. I did what I thought was a DER on my small condo in the Bay Area (turns out my air sealing was probably more on the moderate spectrum). Regardless, while I realize I am in a very temperate climate zone, I can now run the heat pump almost exclusively during the day when solar electricity is produced, and the envelope is good enough to coast through the night at a comfortable temperature. Same for the few days of cooling needed in the summer. This seems like a possibly under-recognized benefit of more dramatic envelope retrofits: Building load shifting capacity for thermal storage prepares us for the expected large role for PV in the future "clean" grid. It dramatically reduces the need for high cost and high embodied CO2 storage, such as batteries, as well as reducing demand on CO2 based sources like gas peaker plants.

    1. brendan_kavanagh | | #26

      We used the BEAM tool for envelope materials and a newer beta tool for mechanicals and refrigerant leakage you can access here,

      We ran lifespan a few different ways and no we didn’t account for load shifting. These calculations can get very complex very quickly and it’s challenging to account for every important variable. Most folks who’ve tried to do this analysis have found that you need to set some boundaries and use assumptions in places and we are wary that can yield some bias in one’s conclusions. We did our best to be fair in the methodology we used and it still shows that DERs perform very well. That said we feel confident both in our practice and the practices of some colleagues that DERs are significantly more expensive and take more time, labor hours, and materials to accomplish often making them not achievable for very large portion of our market. That lack of scalability makes it challenging to make the case that it’s what we should be promoting widely and hence why we’ve shifted our practices, for now…

  8. arioda | | #8

    Gosh, thanks for this article. We have a Victorian home with a new full basement which is the easy part. We have a 5 ton air-to-water heat pump, radiant basement slab with R-20 under it, R5/15 basement walls. Upstairs, the old house has air in most of the walls and is a 1-1/2 story with lots of sloped ceilings. What to do. I have been planning to rip out the plaster exerior walls and furr them out with a little TLC to the window casings. Maybe we just blow in cellulose (R-13) vs the R20-25 we'd get with something in the furred out walls. We are in the Pacific NW Zone 4C so moisture management won't be too tough. Upstairs if I can bring myself to do it, we could pull down the ceilings, spray foam, then furr them down several inches and maybe get to R-20 or so with fluffy stuff under the foam. We have great solar exposure and air sealing well, and window inserts where we need them should do the rest. In summary, this article convinces me that we needn't go crazy and maybe some walls don't need furring out at all or even opening them up. We just take in a little more sun and spit that heat out the envelope via the heat pump which warms the earth up just about the same amount, and we may well save some money and grief. Thanks again for this perspective.

    1. spraggins | | #10

      I’m in the near same situation, 115 year old Victorian that we just got finished lifting for a new basement of the same specs. Our south side had been “energy retrofitted” by a previous owner a decade or two ago and is now a literal rotten mess due to disregard to moisture management. I’ve actually found 4C to be a bit challenging compared to other CZs I’ve worked in.

      1. Deleted | | #12


      2. arioda | | #14

        I deleted a long reply comment because it was off topic tho I would like to hear more detail off-line about your rot situation Spraggins.

  9. n7ws | | #9

    One lesson learned, except for improved comfort, little of this makes sense without subsidies (i.e. someone else paying for it). Next things to learn, there is no climate "crisis" and plants love CO2.

    1. maine_tyler | | #11

      Ahh, plants love CO2! If only the climate scientists knew that. We need more brilliant blokes like yourself calling the shots.

      1. n7ws | | #13

        Despite your sarcasm you are actually correct.

        1. maine_tyler | | #15

          Sarcasm? No no no. I genuinely believe we need more people in power who take basic science 101 facts and presents them as counterevidence to complex bodies of science. And, with the confident (who needs humility?) to think they are the smartest chap in the room. Not enough of these people for sure.

          1. Expert Member
            Michael Maines | | #16

            Imagine the hubris necessary to think that climate scientists don't consider a basic fact we all learned in junior high school, or earlier.

          2. n7ws | | #17

            I've made enough trips around the sun to remember this:

            In 1970, Stanford professor Paul Ehrlich published a famous book, The Population Bomb, in which he described a disastrous future for humanity: “The battle to feed all of humanity is over. In the 1970s and 1980s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now.”

            I think about this every time I hear, "global warming", "climate change" and "climate crisis." To mix a metaphor, The words may be different but the melody lingers on.

            I think George Carlin said it best: (not for tender ears)

          3. Expert Member
            Michael Maines | | #18

            And you don't think anything has changed in the last 53 years? No additional research, no additional understanding of global dynamics, no additional carbon emissions? One prediction that didn't entirely come true (though millions HAVE starved...) and all science is suspect?

            Fortunately in recent years more people at least understand and accept that climate change (or, more accurately, catastrophic climate disruption) is happening and at least partly caused by human activities. Now the questions are mostly how much is caused by humans and what can we do about it. Those who agree with your line of thinking are changing their minds, or dying off.

          4. Expert Member
            MALCOLM TAYLOR | | #19


            In our post-truth society is there is any point engaging with these sorts of statements? As the Irish say: Save your breath for cooking your pie.

          5. Expert Member
            Michael Maines | | #20

            Malcolm, while I have zero expectations that my comments will change the mind of the commenter, I feel like not addressing it is tacitly approving it. If we let our guard down, the city will fall. But I do have better things to do...

          6. Expert Member
            MALCOLM TAYLOR | | #21


            I understand, but also agree with the advice of George Bernard Shaw:

            “Never wrestle with pigs. You both get dirty and the pig likes it.”

          7. maine_tyler | | #22

            If by 'there is no climate crisis' you mean in the way George Carlin did... then yeah sure. The planet will be fine. We won't. Not sure if you missed his entire point or if you just mean that you're not worried about humanity's fate.

            If humans leave in the nearish future is that so bad? Perhaps not and in that sense, not a crisis!

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