Exterior Rigid Insulation - What are our actual sustainable product options?

I’ve been thinking about exterior rigid insulation a lot recently. We know rigid exterior insulation is generally a good thing, it reduces thermal bridging, improves thermal comfort, and improves energy efficiency during operations.

That said, everyone these days loves to celebrate mineral wool, but if you look at the EPDs, you will find that the high density rigid boards (the products used for exterior applications) have a very large upfront carbon footprint.

  • RockWool ComfortBoard80 = ~6 kgCO2e per m2 @ RSI-1
  • NAIMA’s Industry standard high density mineral wool board = ~9 kgCO2e per m2 @ RSI-1

If we look at foam products, we can find a much lower carbon intensive option, but these products are made with petroleum…

  • EPS Industry Alliance standard expanded polystyrene = ~2.8 kgCO2e per m2 @ RSI-1
  • Neopor’s Graphite Infused EPS = ~1.85 kgCO2e per m2 @ RSI-1
  • PIMA’s standard polyisocyanurate = ~4.3 kgCO2e per m2 @ RSI-1
  • Hunter Polyiso Wall Board = ~2.5 kgCO2e per m2 @ RSI-1

From what I can tell, the lowest upfront carbon plant/animal based insulation products (cellulose, straw, wood fiber, etc.) are intended for interior frame wall cavity use. This makes products like TStud (https://www.tstud.com/) way more interesting to me, because you may be able to get away with cavity only insulation due to its reduced thermal bridging and improved framing factor.

SO… this is the conundrum that has been invading my brain space these past few weeks. Do we continue to support petroleum based foam products that have a smaller upfront carbon footprint, or do we choose mineral wool that is technically(?) a “biobased” product, but has an inherently large upfront carbon footprint??

Or is there anything we can do to push mineral wool manufacturers towards using renewable energy in their manufacturing processing? I saw that Rockwool lost the battle to use coal in their new plant in West Virginia. But, it has been replaced with natural gas…so still fossil-fuel based.

Would love your thoughts!


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Hi Scott,

That is a great question. I don’t have a direct answer, but a few observations:

Interesting conversation:

I assume that the EPDs for rockwool are so high because they take into account fossil fuel use during manufacture. With the EPS the fossil fuel is in the product, rather than an externality. So I’d just go with the numbers and prefer the petroleum product.

However, be very careful which petroleum based insulation. I’ve seen huge GWP variability, especially with XPS and spray foam.

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Yes, mineral wool has a higher than expected A1-A3 impact due to the energy intensive manufacturing process. If manufacturers could utilize renewable energy for this process, it would greatly lower its impact. I’m waiting to see if Rockwool will issue a new EPD for the West Virginia plant since it is supposedly using natural gas instead of coal.

Agreed on huge variability. I tend to not recommend a product unless there is a specific EPD for it. I do not like to rely on industry generic/wide EPDs.

We use PPAs to source renewable electricity for our Thermafiber plants. This value does not get reflected in the main results table in the EPD due to the way the UL PCR is written for Construction Products. It can only be reported in the additional information section of the EPD (not sure how many people make to page 29). As such, it does not get pulled into tools like EC3.

Our EPDs published last year have significantly lower values than the NAIMA industry average EPD and our previous EPDs. Depending on which product fits your application, there are scaling factors available for a more exact answer than relying on a high level average. It is also facility specific to comply with Buy Clean CA.

Thermafiber EPD - https://www.owenscorning.com/dms/10019415
Thermafiber Formaldehyde-Free EPD - https://www.owenscorning.com/dms/10023691

In addition, there are Optimization Summaries for both products if looking for products qualified for the LEED EPD Option 2 credit

You will see there are still fossil fuels in the process (coke & natural gas), but it is a journey. We have a lot going on with our Paroc facilities in Europe to electrify the process to remove the cupola and can use those learnings in the future for US processes.

Cheryl Smith
Product Sustainability Strategy Leader
Owens Corning

@cheryl.smith thanks for sharing this and your perspective!

It is interesting to see how the purchasing of renewable energy (off-site) is considered… and that it is included but buried at the end of the EPD.

I’m very curious to see what sort of improvements come out of your facility electrification process. Please keep us posted!

I’ve used Steico wood fiber exterior insulation for above grade applications. I also know of Gutex who manufactures a similar product and Go Lab, who will begin manufacturing in 2023 (hopefully, the date keeps getting pushed back).

Steico and Gutex are both based in Germany, I believe, so embodied carbon from transportation needs to be taken into account, but if you include stores carbon these products come out way ahead of other exterior products I’ve seen.

I’ve also heard of hempcrete as an exterior insulation, but I can’t speak to the embodied carbon of that material.

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@jharmony shortly after posting this thread, I looked into Gutex and saw that it could be used on exterior applications.

Their EPD is reported in different units than I’m used to seeing (m3), so I’ll have to dig in a bit deeper. That said, if you include Stage D, you have a carbon negative product. Like you mentioned, we’d just need to factor transport from the EU to NA.

Hi Scott! Great Presentation at the PH Accelerator this week!
Thought I would reply with some thoughts here:

  • Since Product Category Rules are still created by the industry themselves, I really wonder if fossil fuel derivatives such as plastics, are really accounting for their impact. There is a recent report that summarizes some new public data about plastic, and how fracking is creating availability of cheap feed stocks and the real impact on GHG emissions is just being understood.
    REPORT: The New Coal: Plastics & Climate Change — Beyond Plastics - Working To End Single-Use Plastic Pollution
  • Wood fiber insulation we are also a bit wary of because we also have a biodiversity crisis and forestry practices dont seem to be where they need to, to ensure we should advocate for more wood use.
  • Mineral wool is a mixture of slag+stone (some have more stone than others). Anyway, it seems this product has a path forward to de-carbonize, if slag comes from electric arc furnaces and high heat processes are run on renewable energy (including green hydrogen).
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Thanks @SBayer !

I’m glad you enjoyed the presentation on PH Accelerator! Great questions :smiley:

I do think you are right, mineral wool seems like a logical winner, but they really need to decarbonize their manufacturing process. It just irks me that so many people blindly back mineral wool when it is not the most carbon friendly insulation product right now… and if we are trying to reduce embodied now, are we doing ourselves a disservice by blindly spec’ing it on every project.

Scott I would like to express solidarity with your irked experience. There is so much to evaluate and balance in the construction industry field, that we rely too often on rules of thumb and general frameworks. But we have so little time to solve the climate crisis, and things are changing so fast, that we really need to question everything, check, and then check again! We must lower GHG emissions right now in all aspects of life that we have any influence over. Yet, there are other angles to look at regarding material choices in this regard, that you are most likely already thinking of and that I have been grappling with, so I hope you don’t mind me putting some pen to paper here.

One can see these material choices as part of a larger way to influence the market. As you said some foam plastic insulation products are showing lower GWP numbers from their EPDs than other products. But they are made from a material source that is desperately trying to find ways to keep fracking and drilling. They see the writing on the wall, in terms of energy and transportation. Plastics are the fossil fuel industry’s plan B. I see material selection not only as a calculation of immediate GHG impact, but a ways to promote growth of a material industry source in general.

Now, if we can really make products from fossil fuels in a GHG net zero, pollution free way - I would really like to hear that. But, right now its far too polluting to come even close, and the industry as a whole is not even trying. So, I am working to find ways to eliminate it from every application where it is not necessary, and where it cannot be replaced with other options that have clearer paths to de-carbonize. This will naturally drive investment away from fossil fuels, so that one day (hopefully soon) its price actually reflects its benefit/costs to humanity. From how pervasive and useful plastic products are, it seems that there will always been some functions that are really best met from this material. I hope that the efforts of some pioneering green chemists such as Pete Myers find ways to make it less toxic.

Also, to be honest I don’t fully trust those lower GHG numbers for plastic products. Perhaps I need to dive deeper into some EPS EPD’s. But just like product category rules for wood has historically not accounted for forestry practices, PCRs for plastics may be missing significant emissions, such as leaks from natural gas fracking and piping has finally been understood to release far more methane than originally reported. Additionally, plastic products including insulation, have a large release in stage D of their EPD’s usually, that represent its breakdown in the environment or incineration. Lastly, plastic insulation contains biocummulative chemicals (even if they have removed previous versions, they are replaced with similar ones that have unstudied consequences and doesn’t necessarily mean they are better.)

Every time I talk to someone from a mineral/stone wool company, I press them as to when they will get to carbon neutrality!

Here are some of my go to resources:

and the one I sent before, it will infuriate you:

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@SBayer - hand clap emoji x 5000000

Thanks for this wonderful summary.

I am specifically interested in what you mention about appropriate accounting for secondary (as it pertains to EPDs anyways) impacts, like leaks, during the extraction process. How do we know if the EPDs are accounting for this appropriately?

Maybe @cheryl.smith can chime in, since that is her realm.

For things like polystyrene plastic, we are currently relying on the public data (ecoinvent), so I would refer you to their documentation as to how they handle leaks during production, etc.

There was mention in an earlier post about large releases in the D stage for plastic insulation. This is a worst case assumption for landfilled product to make sure all possible residual blowing agenda emissions are reported. If the product is landfilled without extensive grinding, the blowing agent could remain trapped and continue to diffuse at a very slow rate. There have been initiatives in Europe where landfill regulations provide additional drivers to promote recycling opportunities to recover polystyrene, blowing agent and HBCD. Unfortunately, it looks like even with regulatory drivers, they weren’t profitable enough to stay in business. https://polystyreneloop.eu/ With the (lack of) landfill regulations in the US, it is challenge to develop the infrastructure to get materials like polystyrene or fiberglass back to be able to use in new products. We use a lot of recycled glass cullet and some recycled polystyrene, but run into challenges of reliable supply.

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Thank you Cheryl. Very interesting. Few thoughts/questions:

  1. this idea of “urban mining” for materials like recycled glass seems very promising since there are so many uses for post consumer glass! Do you know of any cities with good recovery rates and what their regulations are?
  2. Recycling polystyrene is also a toxic process as far as I understand. I was once interested in 100% recycled LVT, but then I learned of the inputs during recycling such as mercury, asbestos and PFAS. Now I am looking for ways not to spec LVT at all.
  3. Has there been a desire expressed by the design community to get more familiar with PCR’s? It seems to be the hidden side of how EPD’s are made, and seems the industry itself can choose what gets counted. For that reason I am skeptical of plastic products real impacts, especially considering all the new information that is becoming more widely known about plastics (for example methane during natural gas extraction to feed ethane crackers). Is that a fair skepticism?
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I really think @clfcommunity @clf-admin should do a presentation on PCR’s and EPD’s and discuss these issues/concerns.

This is a great conversation - it really sheds a light to the complexity behind the topic of embodied carbon, EPDs, and PCRs, and the missed information when products are strictly compared based on their published GWP values.

@ScottFarbman to address your earlier question, the ROCKWOOL Group is investing in decarbonizing our operations. We have committed to reducing our carbon intensity (CO2/t stone wool) by 20% by 2020, as well as absolute scope 1 and 2 SBTi by 38% by 2034. A number of our facilities globally are either currently running or have planned conversions to electric melting technologies, specifically in locations tied to a cleaner grid. Our facility in Grand Forks, BC is one of the factories already using an electric melter.

The newest facility in West Virginia uses natural gas which will have lower carbon emissions in comparison to running on coal. We will of course be including our new facility in our EPDs once the appropriate time has passed to collect the necessary data.

Our current EPD is a product specific weighted average between our NA facilities (excluding our newest one in WV), using scale factors to calculate for individual products. The A1-A3 GWP for Comfortboard 80 is approx. 4.1 kg CO2 eq, which is below the comparable NAIMA industry value.

As with all products selected to use in our buildings, taking a holistic approach to evaluating and comparing the benefits is critical. As has been discussed, there are concerns around using foam plastics that don’t appear when you rely on their published A1-A3 GWP at face value such as those shed by Sara.

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@Alejandra.Nieto thanks for joining the conversation! Any idea on when the EPD will be updated to include the electric melter data from Grand Forks?

So to summarize… Product Category Rules (PCR) and thus EPDs… are ripe for manipulation and there is little accountability out there. WTF! I guess I shouldn’t be surprised…

How do we do a better job highlighting these issues and concerns? Calling on CLF (@mlewis) to do a educational series on this.

If anything this makes me more frustrated with LCA. I knew there were challenges, especially around methodology and boundaries, but this is icing on the cake for me right now.

The current EPD in fact includes the Grand Forks facility with the electric melter. However, with the way in which our current EPD has been developed being a weighted average, the individual factory impacts are not viewed separately.
As mentioned, we are planning for an updated EPD to include the newest facility and at the same time, we will look into the best way to share facility specific data.

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Thanks @Alejandra.Nieto, it would be great to see the data at that level.

Yes it would be very good to get facility specific data! I believe there is a larger push for this at the policy level, developing the various types of EPD’s. It might be a good investment for manufacturers to look at policy development in EPDs with this in mind. CLF’s article on this was very helpful:

@carmelpratt and I wrote this summary, if others are interested. Part 2 is coming out soon:

Scott I hope CLF picks up on the idea to have more transparency on PCRs…