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Don't Forget the Science in Building Science


The Case of GWP, XPS, and SPF

Without science, building science is just building.

This week I read and commented on Avoiding the Global Warming Impact of Insulation by Alex Wilson over at Green Building Advisor. I'd avoided the article for a while since climate change isn't what motivates me to do what I do, and I happen to think it may be trumped by a bigger problem anyway (i.e., peak oil).

The article has gotten some building science types in a tizzy, though, mainly because of the recommendation to avoid extruded polystyrene foam (XPS) and closed cell spray polyurethane foam (SPF), two products that are used in a lot of high performance homes. Suddenly, builders feel that they've been misled about using these products.

But are XPS and SPF really the problem the article makes them out to be? I don't hold any pretenses that I was a great scientist during my short stint in academia, but I understand the process of doing scientific research, and reading the article raised some red flags for me.

In case you aren't familiar with the name,Alex Wilson, editor of Environmental Building News the award-winning Alex Wilson is the editor of Environmental Building News (EBN), a great resource for green building information that's been around since 1992. He's well respected, has a reputation for providing in-depth, objective information on various products used in construction, and can recite arcane details about products on demand. I heard him speak at Greenprints this year, and I can tell you, he knows his stuff.

I'm not a regular reader of his blog, but the other articles of his that I've read have been informative and based on solid information. This one, however, seems shaky to me. Please understand that I'm not attacking Alex Wilson; I'm criticizing a particular report that gives the name of building science a black eye.

Briefly, the blog article is based on a longer report in EBN and is a look at the global warming potential (GWP) of different insulation materials. Wilson and his team calculated a 'payback,' the amount of time it would take for the material's GWP to be offset by the GWP of the energy savings they generate over their lifetime. They conclude that you should avoid XPS and closed cell SPF because they have high payback periods.

Here's my take on the problems with the article.

Ask the right questions.

When I read the article, the first question that came to my mind was, why are you looking at the payback over the lifetime of the product? It seems to me that it should be all about the net flow on a year-by-year basis. Does it really matter if the payback is 46 years when the GWP that's offset due to annual energy savings may be higher than the GWP of the offgassing?

They seem to have assumed that the blowing agent is released uniformly over the lifetime of the foam insulation, so if that's the case, all that would matter is that the payback be less than the lifetime. If, however, the entire amount that's released happened immediately, then payback would be relevant. That brings me to my next point.

Show me the data.

Wilson admits in the short article on Green Building Advisor that he's "not 100% sure that XPS is made with [high GWP blowing XPS rigid foam board insulation - bad or not?agents]." He decided on the basis of "various hints in technical literature" to use the high GWP materials in his calculations. In the full article, he says, "Note that the values are highly dependent on assumptions," and "Assumptions are key in this analysis."

To get their results, the EBN team had to assume that:

  • The manufacturers used the high GWP blowing agents.
  • The offgassing profile is uniform.
  • The lifetime of the product is somewhere between 50 and 500 years, though the article doesn't say what numbers they used.
If it's not science, don't pretend that it is.

Science asks the right questions and is based on solid data. If you've done some calculations and created some nice looking graphs, it means absolutely nothing if there aren't any data behind them. It's a house of cards.

One of the commenters on the full article at EBN praised the article as a "rigorous inquiry." If you don't understand how science works, it may look like it is indeed rigorous because it's easy to overlook those statements about the assumptions and focus on the discussion about calculations and the professional looking graphs of payback.

In science, there's this nice little thing called peer review. The way it works is that you can't publish your research without it being looked over by other scientists. This prevents researchers from getting lost in a bubble and believing they've done something magnificent when in fact, they've just concocted a giant fantasy. If this EBN report had had to go through scientific peer review, it never would have seen the light of day.

The term 'building science' is in vogue with green builders and home energy auditors these days, and that's a good thing. But let's remember that science has certain requirements. I was never enough of a theorist to really understand string theory, but I knew enough to see that it was BS (and I'm not talking about building science) because too much of it was based on assumptions that couldn't be tested.

What they should have said

Based on the data available, the EBN team had no justification to recommend avoiding XPS and closed cell SPF. About as far as they could have gone would be something like this:

Some insulation materials MAY use blowing agents with a high global warming potential, and IF those chemicals escape, it COULD be bad news for climate change, depending on how rapidly they're released and what kind of construction they're used in and where the building is. Then again, maybe it's NOT a problem and using them actually helps mitigate climate change. Based on the Precautionary Principle, however, we advocate avoiding these materials until it's certain that the blowing agent has a low GWP.

If they'd said that, the state of building science would be better, and I wouldn't have had to write this article.

In case you're wondering, I have no connection with the XPS or closed cell SPF industries. I like polyisocyanurate and open cell spray foam and probably recommend them more than the other two anyway. I'm speaking out here solely in defense of science.


Thanks for adding your thoughts to that discussion over at GBA....I was really starting to take the article as fact and you made me stop and think it through. It's really difficult to comprehend 'lifetime' comparisons of paybacks and GWP etc. since there are so many factors involved over that amount of time...especially in the face of catastrophes like the gulf oil spill.
Posted @ Wednesday, August 11, 2010 7:57 PM by Hunter D.
You're welcome, Hunter. That it was creating doubt and confusion and possibly changing behavior and attitudes toward what are probably perfectly good products is exactly why I wrote this article. Yes, it IS difficult to understand these issues sometimes. As I said above, it's easy to overlook the statements about assumptions and instead focus on the nice looking graphs. 
I had a conversation with someone today about this topic, and he said they'll be releasing a better examination of this issue in the next few weeks. As soon as it's out, I'll announce it here in this blog, too.
Posted @ Wednesday, August 11, 2010 8:29 PM by Allison Bailes
Great article, Allison. 
If you're interested, here's some solid science to dig into. 
NSF-verified Eco-Efficiency Analysis for open-cell and closed-cell spray foam: 
NSF-verified Eco-Efficiency Analysis for WALLTITE ECO closed-cell spray foam: 
Some background info on the Eco-Efficiency Analysis methodology: 
I will openly declare at this point that BASF Construction North America is one of my clients. 
Posted @ Thursday, August 12, 2010 7:48 AM by Stephanie
Great article Allison, I concur with your assessment. I too have a problem even with the term Global Warming Potential. How do you define "potential"? The Gulf Oil spill was suppose to have a high EDP (ecological disaster potential) but it seems no one took into account the earth's potential to scrub the oil through natural processes. Now its not a major disaster anymore. Actually I think I remember an article that showed the process used to clean up the Exxon Valdez spill (high pressure cleaning of the rocks on the shore)actually has made the rocks sterile unable to support moss or algea.
Posted @ Thursday, August 12, 2010 8:02 PM by Bruce Chyka
Allison--as you know I've been crowing about not letting the GWP foam scare paralyze efficiency. Still, I think all of us need to be keeping the pressure on the replace the high GWP blowing agents. Us geeks can do the math and arrive at well conceived decisions about the tradeoffs. But the growing realization amongst the general populace that some of these materials have a GWP that is 1400+ times CO2 is a public relations nightmare we'll never win. I believe the reason Alex wasn't definitive on the XPS blowing agent is because the manufacturers didn't disclose it to him. It took me 3 minutes to track down the MSDS and find that it includes 1,1,1,2-Tetrafluoroethane, aka HFC-134a. This, according to sources I've seen, has a GWP of 1430.  
At #bscamp, Honeywell admitted that HFO and HFE blowing agents were close. They have a GWP of 6-15 they said, and a 4-6% IMPROVEMENT in R value!  
I'm with you on the importance of the science, but this is a perception issue that I don't think we can win. Time for the manufacturers to get these new blowing agents out of the lab and into the market now, not in two years.
Posted @ Saturday, August 21, 2010 2:24 PM by Peter Troast
Peter, if the EBN article had made the same argument you just made, I never would have written this piece. Instead, Alex tried to calculate global warming potential due to chemicals in some foam insulation types with so much uncertainty that his results were meaningless and misleading.  
As I said above, I don't think climate change is the biggest problem we're facing now. It's peak oil, and that requires reducing our energy use as much as possible.
Posted @ Saturday, August 21, 2010 3:14 PM by Allison Bailes
Always interested to read your posts.what are the outgassing issues on closed & open cell foam ? I hear conflicting opinions .The link for spraying foam the installer only uses a particulate mask !? He mentions in closed spaces using a fan . Isn't a proper filter mask required? How variable is it from product to product ? Sincerely , TD Davis
Posted @ Thursday, December 06, 2012 1:13 PM by Tim Davis
Wow, don't I feel like a jackass. I drank that Alex Wilson tea, without actually reading the Alex Wilson "research" paper. Trained as a cancer biologist with several years in the pharmaceutical industry after my postdoc, I know better than to listen to a non-scientist describe a scientific paper and then believing what the non-scientist said the authors of the scientific paper concluded. Yet, this is exactly what I did when I read a article on the Alex Wilson paper through some website and suddenly swore off all closed cell foams because of the GWP of the HFC-245a. Worse yet, people actually listen to me around here(northern California) because of my scientific training and now I feel like I have ruined that hard-won respect.  
thank you for reminding me that respect is earned through hard work and due diligence and that if I'm going to preach the benefits or detriments of something to people who don't have my training, I need to do my own research, whether that be my clients, my colleagues or my workers, The old "trust but verify" rule that was so frequently beaten into our minds during graduate school, needs to be beaten in to my mind a few more times I guess.  
Thanks Allison, I will make that mistake again. And unfortunately I'll get in less sleep than I already do. Happy holidays.
Posted @ Sunday, December 23, 2012 3:29 AM by David Edwards PhD
I meant I wouldn't make that mistake again. Stupid typo.
Posted @ Sunday, December 23, 2012 3:32 AM by David Edwards PhD
I've used/reconsidered spray-foam for awhile and the I think the IPCC (peer review) now confirms much of what Wilson was concerned about: 
"The use of hydrocarbon and carbon dioxide as blowing agents for polyurethane and extruded polystyrene insulation foams is expanding. A recent European study (Harnisch and Hendriks, 2000) estimated that by 2010 about 50% of all polyurethane and extruded polystyrene foams in this sector will be blown by hydrocarbons and carbon dioxide, respectively."  
Please correct me if I'm wrong. 
Posted @ Saturday, May 10, 2014 10:38 PM by Shawn
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