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Building Science

More About Global Warming and Insulation

It’s not as straightforward as many seem to believe

The global warming impact of insulation seems pretty clear from this graph. But what are the complexities behind these lines?
Image Credit: Alex Wilson

Well, I really stirred things up with my last article on insulation and global warming. My intention was to explain why Alex Wilson’s results could be doing a disservice to the green building community. In the end, I was rightly accused of have done a disservice myself.

So, here goes with Part Three of my take on the global warming impact of insulation. Let’s see if I can get closer to the truth this time.

A public apology to Alex Wilson

First, I need to apologize to Alex Wilson. I apologized privately at the time of my last article. Now I do so publicly. I wrote things that went too far, saying his results were bogus and he was engaging in pseudoscience. I regret those comments and have removed them from that article.

As I’ve said before, Alex Wilson has done great work in his career. He’s taken green building further than just about any other person in the field. His Environmental Building News has set the standard for green building news and analysis for decades. He also has a background in science and takes science seriously.

Wilson’s insulation and global warming study

Since that last article, I’ve done more reading of Wilson’s 2010 article, Avoiding the Global Warming Impact of Insulation, and related works, as well as discussing it with others. Briefly, what he did was to calculate the amount of time a highly-insulated wall assembly would have to be in service to “pay back” in reduced carbon emissions the amount of global warming created by the insulation itself. That insulation impact, he stated, comes from two things: the embodied global warming potential (GWP) and the GWP of the blowing agents used in foam insulation. His conclusion was that extruded polystyrene (XPS) and…

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  1. User avater
    Alex Wilson | | #1

    Thanks Allison
    These are exactly the sorts of issues that I had hoped would be raised by my original article. Your pushback on some of my assumptions is justified and, as you correctly note, the conclusions one draws will vary depending on the assumptions used. It's a complicated issue. Nice job with this blog.

  2. User avater GBA Editor
    Allison A. Bailes III, PhD | | #2

    Response to Alex Wilson
    You're welcome, Alex. Thank you for commenting. Sorry it took me so long to get to this point. I'm a bit slow at figuring things out sometimes.

  3. Charlie Sullivan | | #3

    Between a rock and a soft place
    If our only option for good insulation was high GWP foam, we'd be between a rock and a hard place--the rock being using lots of fossil fuel to heat a building that had no* or little insulation, and the hard place being the use of substantial amounts of high GWP foam. We'd then need to fret about making the right choice, which would require doing this kind of analysis, and making sure we had the right assumptions built into it. David White's spreadsheet would be an essential tool.

    But that's not the world we live in. We not only have the rock and the hard place as options--we also have a soft place: piles of fluffy cellulose. Or mineral wool, EPS, neopor, polyiso, open-cell spray foam, and now even Lapolla's 4G closed cell spray foam blown with low GWP HFO blowing agent. So we can all relax and stop losing sleep over exactly how bad HFC blowing agents are. They are clearly much worse than the alternatives in terms of GWP, and you can use other materials that don't have that problem to achieve the same result.

    For example, if you prefer to avoid a separate step for air sealing in addition to insulation (e.g. if you don't have a crew or contractors you can trust to do air tight drywall or membranes, but you do have contractors you trust to do the spray foam and to mix the chemicals right), you can use open cell foam in most places and Lapolla 4G where you need low vapor permeability.

    When Alex wrote his original article, there were a few situations, such as a field-stone foundation wall, where it was truly hard to find a good-performance low GWP option. But that's no longer the case. There are low GWP options for any requirement.

    *Footnote: A comparison with no insulation as the alternative is a red herring as no GBA reader would build that way, but that seems to be what Allison suggests, so include that for completeness.

  4. User avater GBA Editor
    Allison A. Bailes III, PhD | | #4

    Response to Charlie Sullivan
    Good points, Charlie. But the main takeaway should be that we can't talk about GWP of individual materials in isolation. They're part of the bigger system of the building they're incorporated into.

    Also, I certainly am not suggesting comparing any scenario to a scenario with no insulation. That was true in my article on the diminishing returns of insulation and it's true here.

    What I said was that, for example, if you were building a house and using Lstiburek's Perfect Wall, you'd have insulation only on the outside and no cavity insulation. All of the energy savings would accrue to the exterior insulation, whether it be XPS, mineral wool, or something else. The payback in that case would be much more favorable for the high-GWP insulation materials. If you can get a 10 year payback with XPS or closed-cell spray foam, even with the HFC blowing agents, then you can't eliminate them from consideration on the basis of GWP. You might have other reasons not to use them, but the GWP argument would fail.

  5. Derek Roff | | #5

    Fainting with damp praise
    I appreciate your willingness to revisit this topic, and recognize that some previous comments had validity. However, by your count, this is your third article on the topic, and pretty much all of it is focused on disagreements with a six year old article. I think it's time to hear from Allison on Allison. Suggested first sentence, "I disagree with some things Alex wrote six years ago." Next 100 sentences expand on: "Here is how I would do the analysis today, what I see as the important factors, and what the data shows when we run different scenarios for common situations in this country." You give us hints at that in this article, but I would love to see you present your stand-alone coverage of this topic for 2016, start to finish from your viewpoint and priorities.
    Rather than getting just a taste of your approach, presented in reaction to Alex's previous article.

  6. User avater GBA Editor
    Allison A. Bailes III, PhD | | #6

    Response to Derek Roff
    The article today concludes with where I think this needs to go. And indeed I'm looking into helping to take it that next step along the path. I've just submitted an abstract to speak on this topic at the North American Passive House Conference in Philadelphia. Once I have something to show, I'll be sure to publish it here, too.

  7. KEVIN ZORSKI | | #7

    Allison - Thank you for revisiting this topic. Some of your arguments are good for pointing out the limitations of Harvey's paper and Alex Wilson's covering of it. Some are not so good. For one, The" whole wall might be different from the added to wall" argument matters little. In either case one is adding insulation to achieve a certain R-value. The fact that these foams emit a lot of global warming potential gases, compared to other choices that could do the same thing with significantly less GWP is still a valid point. Secondly, you're confusing two separate but important issues when you start talking about economic payback. An insulation may have a great payback but still be horrible for the planet. Any mention of the payback periods of different insulations has no significant place in this discussion, which is about GWP. Third, the type of energy running the building also has no effect on the GWP of these insulation choices. It doesn't matter whether you have photovoltaics, hydropower or burning old tires. The production of these foams uses products that in and of themselves cause their own GWP, irrespective of the energy source of the home. That would be a separate and interesting article. How much energy is saved at the house, or how many dollars are saved, again, another issue. A valid point you raise is the GWP of the whole building assembly. Double wall houses need more framing, and often have more layers of sheathing, to be used as air barriers. Other wall systems would need less embodied energy in the form of, say, sheets of plywood. (Another variable is the GWP of the disposal of various products at the end of there useful life.) As far as I am concerned, the bottom line is to not use these products when there are other choices available. Thanks again for keeping this discussion alive, It's an important one.

  8. Keith Gustafson | | #8

    The reason money is important
    The reason money is important in the discussion is that foam can be used to build an inexpensive assembly. In a retrofit one cannot just add R10 of cellulose and put siding or roofing over it. The cost of labor and supporting structure can easily exceed the cost of the actual insulation. So if foam was not available, no insulation would be added, and so it is the GWP of insulation not added, if you will. This is the same when consider the cost based on heating with oil and coal fired electricity.

    The foam insulation[and other improvements] save at least 600 gallons a year of heating oil in my house, and insulating it otherwise would have been impossible both economically and practically, so the insulation would not have been installed.

    What is the GWP of that?

    The reason Allison's article, and continued discussion is important is that, as in any scientific endeavor, we must be our own harshest critics.

    "foam is bad" is simply not a useful statement

    "Encouraging the building of low GWP building assemblies" is a useful statement.

  9. KEVIN ZORSKI | | #9

    Foam is bad ?
    Keith - There are certainly places for foam, both board and spray, especially when it comes to retrofits. But with new construction there are a lot of other choices, and the use of these products should probably be more judicious. Money is important in most discussions on insulation. Trust me, I'm extremely frugal. But in regards to this GWP arena, it clouds the argument of GWP - R value of various insulations. I certainly did not say "Foam is bad."

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