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Can insulation materials, which we use to save energy and help prevent climate change, cause greenhouse gas emissions? Yes, in two ways. First, it takes energy to produce and ship these materials--which we refer to as "embodied energy"--and using fossil fuels for these energy needs releases carbon dioxide (our most significant greenhouse gas). So in a sense, all insulation materials have embodied global warming potential (GWP). Second, two of our common insulation materials are made with hydrofluorocarbon (HFC) blowing agents that are very potent greenhouse gases. Extruded polystyrene (XPS), best known by the brands Dow Styrofoam ("blueboard") and Owens Corning Foamular ("pinkboard"), insulates to R-5 per inch and is made with HFC-134a, which has a GWP of 1,430--meaning that it's 1,430 times as potent a greenhouse gas as carbon dioxide. (I have to note here that I'm not 100% sure that XPS is made with HFC-134a; manufacturers are unwilling to divulge the exact blowing agents they use, saying the information is proprietary, and material safety data sheets have not been updated yet to reflect the new blowing agents that were required as of January 1, 2010. But various hints in technical literature have led me to believe that this is the blowing agent being used.) The other insulation material made with a high-GWP blowing agent is closed-cell spray polyurethane foam (SPF). This insulation material is sprayed into building cavities, onto a foundation walls, or onto roofs, and it insulates to about R-6 per inch. Most, but not all, closed-cell SPF is made with HFC-245fa, which has a GWP of 1,030. Some closed-cell SPF is water-blown, thus avoiding this concern, though the vast majority is HFC-blown. Open-cell (low-density) SPF, such as Icynene, is all water-blown, so has a very low GWP. Lifetime GWP A blowing agent with a high GWP is only problematic if that chemical leaks out over time and, unfortunately, not much is known about how quickly this occurs. Some researchers, such as L.D. Danny Harvey, Ph.D., of the University of Toronto (who first raised the concern about the high GWP of foam insulation materials in a technical article a few years ago), has assumed that a large majority of the blowing agent leaks out over time, but based on conversations with technical experts in the industry, our analysis in Environmental Building Newsadopts a more conservative assumption that only 50% leaks out over the life of the insulation--which could be 50 years or 500 years.

Click the image to view the table.

When we combine these two sources (embodied GWP and GWP related to the blowing agent used) for an insulation material, we arrive at the "lifetime GWP" of these materials. For insulation materials made with HFC blowing agents, the vast majority of the total GWP comes from the blowing agent. See the table for the assumptions we used in the EBN article. Payback of lifetime GWP

Click the image to see an expanded version of the chart.

If we then calculate how much energy a given amount of insulation will save over its life (which depends on where the house is located and how efficient the heating system is) we can calculate the "payback" of the lifetime GWP in the insulation. In other words, this is the length of time it will take for the energy savings from the insulation to pay back the greenhouse gas emissions that will result from the use of that insulation. With the help of John Straube and Daniel Bergey of Building Science Corporation in Westford, Massachusetts, we calculated the paybacks for adding different amounts of these insulation materials. This is reported in the June issue of Environmental Building Newsfor those who want to see the analysis in more detail. We looked at adding R-5 increments of insulation to a 2x6 wall system insulated with dense-pack cellulose (whole-wall R-value of 14 for the starting wall). The energy model assumed the building is in a moderately cold Boston climate. This is shown in the two charts. The good news is that, except for XPS and HFC-blown SPF, the payback for the lifetime GWP of insulation materials is very low. If you add four inches of polyisocyanurate (R-25) to the 2x6 wall, for example, (R-39 total) the lifetime GWP payback for that added polyiso insulation would only be 2.7 years. Even if you go all the way to a final R-60 for the wall system (adding 7.5 inches of polyiso), the payback would be only slightly over four years.

Click the image to see an expanded version of the chart.

By comparison, if it's XPS you're adding to the 2x6 wall, the payback for that added insulation is much longer. Adding one inch of XPS has a 36-year payback. With two inches, the payback jumps to 46 years, and with four inches, 65 years. To go all the way to a final R-value of R-60 (adding about 9 inches of XPS) would have a payback of over 110 years. For SPF, the paybacks will be similar, though somewhat lower. Bottom Line – Avoid XPS and SPF So what does all this mean? These differences are dramatic enough that, even if our assumptions are off by a significant factor, we can draw some general conclusions about sensible choices. If we're building highly insulated buildings and doing so in part to mitigate global warming, we should use insulation materials other than XPS or SPF--at least until these insulation materials are produced with blowing agents that have far lower GWP. (Low-GWP blowing agents, such as hydrofluoroolefins, HFOs, are likely to be available from Honeywell and DuPont in the next few years, though it is unknown how quickly XPS and SPF manufacturers could convert to these or other compounds.) There are lots of good alternatives. Now that polyisocyanurate (a common foil-faced rigid insulation material sold under such tradenames as Thermax, ACFoam, and Rmax) is made with pentane as a blowing agent, its GWP is very low (the GPW of pentane is about 7). Expanded polystyrene (EPS or beadboard) is also made using pentane as a blowing agent. Open-cell SPF, such as Icynene, uses water as a blowing agent. Fiberglass, mineral wool, and cellulose do not use blowing agents at all. Note that XPS and closed-cell SPF offer some excellent performance properties (controlling moisture migration and airflow through the building envelope), so if we are substituting a different material, we have to address these building science issues carefully. The bottom line is that when we insulate our homes so that they will use less energy and thus help to mitigate climate change, we should be careful about which materials we use. Providing high levels of insulation with XPS or closed-cell SPF will counteract a lot of that well-meaning effort. To get a more complete understanding of this issue and for a checklist of alternatives to XPS and closed-cell SPF, check out the June, 2010 issue of Environmental Building News (to access this article, a log-in is required--$12.95 per week or $199 per year). I invite you to share comments on this blog. Will this information affect your choices of insulation materials? Alex Wilson is the executive editor of Environmental Building News and founder of BuildingGreen, LLC. To keep up with his latest articles and musings, you can sign up for his Twitter feeds.

Photo: Net-zero-energy house built by Bensonwood in which 4" of XPS was used over cellulose-insulated 2x6 walls. The GWP payback on the XPS in this house is about 65 years. Source: Bensonwood. Table and graphs from Environmental Building News, June, 2010.

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1 I really enjoyed your article posted by Filipe Borges de Macedo on 06/02/2010 at 12:41 pm

I really enjoyed your article, but I am surprised that don't mention Expanded Corkboards, the best environmentally isolation material friendly that I know.

2 A Quebec manufacturer of cork posted by Andre Fauteux on 06/02/2010 at 02:59 pm

A Quebec manufacturer of cork told me cork insulation costs a fortune. Filipe, do you know of an American supplier who is competitive? Thanks, André

3 I am also surprised that you posted by Jorge Carvalho on 06/03/2010 at 04:18 am

I am also surprised that you don't mention other cleaner materilas like cork. We have been using expanded corkboards for insulating buildings in Portugal. But, very relevant: we use in this context not only because its production is environmentally almost completely clean but also because the proximity of growing and production avoids transport polution. In other contexts, other clean insulations are available, according to the local resources (lambswooll, strawbails, etc.). In order to be of practical use, the comapartive table must include in a dynamic way (location of use input by the user) the waste and pollution of transport and calculate the overall impact.

4 Andre I work and live in Euro posted by Filipe Borges de Macedo on 06/03/2010 at 02:46 am

Andre I work and live in Europe, compared with other insulation, the expanded corkboards, aren't that expensive, about 20% more expensive, in the north american market, i don´t know. But you could try contacting Amorim, they are the bigest producer,, Good luck

5 In 2008, Owens Corning Celfor posted by Andre Fauteux on 06/01/2010 at 12:30 pm

In 2008, Owens Corning Celfortec's Valleyfield, Quebec plant (where XPS is made) released no less than 351 tonnes of HCFC-142b into the atmosphere and 163 tonnes of HCFC-22, according to Environment Canada's National Pollutant Release Inventory ( Cheers,

6 What is meant by "dense-pack" posted by Heather Gayle Holdridge on 02/04/2011 at 11:26 am

What is meant by "dense-pack" cellulose? Is this the same as blown-in spray cellulose?

7 Heather, dense-pack cellulose posted by Tristan Roberts on 02/04/2011 at 11:30 am

Heather, dense-pack cellulose is blown into cavities, under pressure, at a density of roughly 3.5 pounds per cubic foot. At this density it doesn't settle, offers good R-value, and fairly impermeable to air movement. Cellulose can also be blown into cavities at a lower density, or blown into open spaces such as an attic, also at lower densities, so these applications might be called "blown-in" but not "dense-pack."

8 Current research has shown th posted by Jekin on 07/12/2010 at 11:00 pm

Current research has shown that using food based agricultural products as fuel feedstock has caused major land use changes that has increased global warming.

9 A payback time line that surp posted by Bernard Droege on 02/11/2011 at 10:21 am

A payback time line that surpasses an individuals life span makes not rational sence. Global warming, greenhouse gases, climate change...what does any of this mean when you look at 4 to 5 billion year old goelogical record and see evidence that this is not the first time this has occuered, nor will it be the last... Why blame it all on man and his use of the earths resorces? Someone has a great deal of time on their hands and alot of imagination.

10 1) In Europe XPS is produced posted by Wolfgang Feist on 06/03/2010 at 10:50 pm

1) In Europe XPS is produced without any FCKW. So that would be the very first step: Flour and Chlor shouldn't be used in the foaming agent. You do not need it. 2) As in economy, payback times are misleading. Insulation reduces the overall green house effect, and it is one of the best methods to do so. For a correct analysis a life cycle balance has to be used.

11 One more question -- How can posted by Heather Gayle Holdridge on 02/08/2011 at 01:35 pm

One more question -- How can I find out which closed-cell SPF products are water-blown? Is there a list out there somewhere?

12 Another important source of m posted by Suzane on 09/24/2010 at 10:20 pm

Another important source of methane is a "fermentation digestive tract of cattle," because it is elequontly use. This is really sigificant source of greenhouse gases, and is a weapon that vegetarians use to promote their lifestyle. Since I learned of this, they are actually concisouly eat less meat.

13 Great article, but I don't un posted by Brent Eubanks on 06/15/2010 at 02:55 pm

Great article, but I don't understand the meaning of Payback in the first graph. In the second one, it makes sense because you are comparing the embodied GWP to the GWP that is offset through energy savings. But as far as I can tell the first graph is just comparing the GWP of different insulation -- there is no countervailing effect being considered which would provide a payback. Can you clarify this? I'd like to share it with my colleagues, but want to understand what I'm sharing first.

14 The two graphs are showing th posted by Alex Wilson on 06/15/2010 at 05:29 pm

The two graphs are showing the same thing, but on different scales. The table that's included before the two graphs doesn't show payback, but rather the underlying assumptions on "lifetime global warming potential" (GWP) of the different insulation materials. Data in the last column of the table is used in calculating the paybacks shown in the two graphs. Hope this answers your questions. -Alex

15 Second, there isn’t enough in posted by Effects of Global Warming on 06/28/2010 at 03:57 am

Second, there isn’t enough information in the post to allow a full understanding of the underlying science, methodologies, and assumptions used. An explanation of your methodology would facilitate greater understanding of your conclusions and would allow for a more robust discussion.

16 The interest in additional da posted by Tristan Roberts on 06/28/2010 at 04:16 am

The interest in additional data and information is great. For much more detail, please check out the recent article in Environmental Building News (EBN), "Avoiding the Global Warming Impact of Insulation." The summary information provided in this blog post is derived from that article:

The research, thought, and presentation put into this analysis takes time and resources so our full feature EBN articles are available to our subscribers. To read a single article like this one, an easy option is to get a weekly subscription for $12.95.

– Tristan Roberts Managing Editor, EBN

17 for Bernard - and all others posted by tom balderston on 02/25/2011 at 01:51 pm

for Bernard - and all others who may may hear this argument. take some time and study ecological and geological history. Yes there have been climate changes before, some much more extreme and some we can be glad we were not around for. The problem with the current climate change is that it is happening very fast, and plants/ animals may not adapt - so we could a) lose many many species in the next century or two. b) inflict terrible suffering on many people - especially poor people c) lose some water front property (ie Florida). Though I agree we humans are a part of nature, we evolved the smarts to release the stored energy in the worlds fossil fuels into the atmosphere all in a few hundred years - which is a millisecond to a geologist!

18 Does anyone know whether Wall posted by Teresa on 09/27/2010 at 10:03 am

Does anyone know whether Walltite ECO (TM) Polyurethane Insulation/Air Barrier produced by BASF is an effective insulation product? This company claims not to harm the ozone..and have a near zero global warming potential (GWP) score.

Thanks in advance.


19 After carefully reviewing the posted by Dave Williams on 06/23/2010 at 12:03 pm

After carefully reviewing the data presented above, your blog raises some questions.

First, the data presented appears to be very similar to what has previously been presented by other researchers. Since you have no citations in your post, it is unclear if this is new research or based on existing information. Has any of the information in this blog been published previously?

Second, there isn’t enough information in the post to allow a full understanding of the underlying science, methodologies, and assumptions used. An explanation of your methodology would facilitate greater understanding of your conclusions and would allow for a more robust discussion.

Thank you in advance for taking the time to respond.

Dave Williams Sr. R&D Manager Honeywell International

20 Another important source of m posted by Green Pro on 07/24/2011 at 10:14 pm

Another important source of methane is a "gut fermentation of cattle," because he eloquently necessary. It's really a source of greenhouse gas emissions significant and is a weapon that vegetarians use to promote their lifestyle. Since I heard about this, they are actually consciously eat less meat.

21 I am very pleased to see that posted by David Brooke Rush on 06/22/2010 at 10:31 am

I am very pleased to see that Cellulose Insulation appears to be the best choice for the most cost effective and environmentally friendly type of insulation in your charts. I have been using Wall Spray Cellulose Insulation in our walls for last 25 years. I selected it for its recycled qualities along with the ability to build custom sized batts in every wall. I know the "installed" R value is superior to other batt insulations. Along with our air sealant work, air tight drywall approach and Cellulose in the walls, we are building a durable high efficient house that will last for years to come.

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