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Making Healthier, Greener Foam Insulation

A proposed change to the International Residential Code would eliminate the need for halogenated flame retardants in many applications

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For this Passivhaus in New York's Hudson River Valley, 12 inches of XPS were installed beneath the concrete slab. With proposed changes to the IRC, subslab insulation wouldn't need to be treated with flame retardants.
Image Credit: Jordan Dentz
For this Passivhaus in New York's Hudson River Valley, 12 inches of XPS were installed beneath the concrete slab. With proposed changes to the IRC, subslab insulation wouldn't need to be treated with flame retardants.
Image Credit: Jordan Dentz
A house under construction in Naperville, Illinois, is wrapped in XPS that will be thermally separated from the living area.
Image Credit: Alex Wilson

As readers of this blog know, I’ve come down fairly hard on certain types of foam insulation over the years. The downsides include the blowing agents used in extruded polystyrene (XPS) and most closed-cell spray polyurethane foam and the flame retardants that are added to all foam-plastic insulation to impart some level of fire resistance.

Now there’s an effort afoot to change building codes in a way that would allow manufacturers to remove the hazardous flame retardants. This is the subject of a just-published feature article in Environmental Building News (log-in required).

This is a significant energy issue, because layers of foam insulation provide the easiest way to achieve the level of energy performance needed to approach net-zero-energy performance. If we’re going to add a lot of foam insulation to our homes, we want that to be safe for the occupants and the environment.

Flame retardants used in foam insulation

We don’t want insulation materials to catch fire, so it is logical to add flame retardant (FR) chemicals to these materials if it will prevent them from catching fire. That’s the reason HBCD (hexabromocyclododecane) is added by all polystyrene insulation and TCPP (Tris [1-chloro-2-propyl] phosphate) is added to most polyisocyanurate and spray polyurethane foam insulation. These are both halogenated flame retardants — the first using bromine, the second chlorine.

The problem with these halogenated flame retardants is that they have significant health and environmental risks. The HBCD that is used in all polystyrene (both extruded and expanded) is being targeted for international phase-out by the Stockholm Convention on Persistent Organic Pollutants. It is highly persistent in the environment and bioaccumulative in the food chain; it is believed to cause reproductive, developmental, and neurological impacts. Less is known about the TCPP used in spray polyurethane foam and polyisocyanurate, but there is significant concern in the health and environmental community.

Building codes require that foam-plastic insulation meet a very specific flammability standard. But building codes also require — for most applications — that foam insulation has to be separated from living space by thermal barriers, such as gypsum drywall.

The efficacy of flame retardants compared with thermal barriers

Combustion studies that were done in the 1970s showed that if the insulation is not protected with a thermal barrier, there is no correlation between the presence of flame retardant and the extent of the resultant fire. Thus, the inclusion of a flame retardant does not seem to appreciably increase the fire resistance of foam insulation, according to a peer-reviewed technical paper recently published in the journal Building Research and Information.

However, thermal barriers like 1/2-inch drywall work extremely well at containing fires. The 15-minute protection provided by 1/2-inch drywall gives occupants time to escape a fire. In other words, of the two measures used to impart fire safety to a building assembly (flame retardants in foam insulation and thermal barriers) almost all of the fire safety benefit is provided by the thermal barrier.

Changing building codes to allow elimination of flame retardants

Because the vast majority of the fire safety in a building enclosure is provided by the thermal barrier, a group of environmentally aware architects, chemists, and code experts is seeking to change building codes to allow non-FR foam to be used in applications where adequate protection is provided by a thermal barrier. (Full disclosure: I have been involved in this initiative.)

The code change would allow the FR-free foam to be used below-grade, where the insulation is sandwiched between concrete and earth (hardly a fire risk), and where the foam is separated from the living space by a 15-minute thermal barrier, such as 1/2-inch drywall.

For the former application (below-grade insulation), I believe it’s a no-brainer. Over half of XPS is installed below-grade, so I think there could be a very viable product free of flame retardants for this application. The change to building codes wouldn’t mandate the elimination of flame retardants, but it would give manufacturers the option to do so if they chose to. Eliminating the flame retardant for above-grade applications where there is a 15-minute thermal barrier isn’t a slam-dunk, but I believe the case being made is strong.

Changing building codes, however, is a long, challenging process; I don’t know what chances the initiative has. In my article research, manufacturers expressed reservations that they don’t want to have to produce, distribute, and market two different lines of material, and they point out that they also have to be concerned with fire safety of material being stored and during construction (before drywall is installed).

On the other hand, though, foam insulation manufacturers spend a lot to incorporate flame retardants into their products. The insulation contains a not-insignificant amount of these chemicals: 12.5% TCPP in open-cell spray polyurethane, 4% TCPP is closed-cell spray polyurethane, and 2.5% HBCD in extruded polystyrene. A lot of the strategies for “greening” building products increase the manufacturing costs, while removing expensive flame retardants should reduce costs. So there is some interest by the industry in this change.

As described in our Environmental Building News article this month, “Getting Flame Retardants Out of Foam Insulation,” the code-change initiative is being targeted, initially, at the International Residential Code. If successful, an effort to change the International Building Code (for commercial buildings) will follow.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. In 2012 he founded the Resilient Design Institute. To keep up with Alex’s latest articles and musings, you can sign up for his Twitter feed.


  1. greenophilic | | #1

    Flame retardants effects on foam quality
    Alex, I believe that many polyurethane foam manufacturers for furniture and such purposes feel that added flame retardants actually lower the quality of their product, i.e. lessening its performance. Are you aware of any similar performance degradation in board foam products due to inclusion of these FR chemicals?

    While I think that non-FR foam should be available, I think the issue of manufacturers not wanting to produce two products is non-trivial. As you know, avoidance of doing this led to the inclusion of high levels of FR chemicals in poly foam furniture throughout the US due to laws requiring them in CA. Is there really a large enough market for non-FR foam, given that, at present, essentially no green building certification systems rewards it? I know LEED is piloting such a chemical avoidance credit, but that is all, aside from the living building challenge.

    Giving manufacturers the option to not put FR chemicals in their products is a good first step, but what we really need is better regulation and forced removal of these chemicals from products where they are not absolutely crucial.

    Thanks for your post and efforts on the topic.

  2. Alex Wilson | | #2

    On two product lines for foam insulation
    You make very good points. It would be up to manufacturers to decide whether the costs of developing, warehousing, shipping, and marketing a non-FR foam along with a traditional foam would be warranted. I believe that below-grade represents about 60% of the XPS market, though that that may be a guess that someone in the industry provided to me. The market for above-grade XPS and polyiso where the foam is separated from the living space by minimum 1/2-inch gypsum board is probably over 95% (just a guess) and even higher for residential applications--but the argument isn't quite the slam-dunk for non-FR there in my opinion.
    I'm afraid that I don't have a sense of how the FR affects the foam insulation performance; I've never heard that it degrades the insulation performance in any way.
    BTW, with polyiso when CFCs were used as the blowing agents there was no need for FRs, and they were not used. But in switching to a blowing agent that was less damaging to the stratospheric ozone layer, more flammable blowing agents replaced the CFCs and separate FRs were added.

  3. bencarsan | | #3

    Foam isn't green
    Thanks Alex. This issue is enormous and I am continually surprised at how little attention it gets. As with tabacco, industrial food, climate change and so many other issues, industry goes to great lengths to use marketing and political muscle to drown out all of the disturbing things that scientists are trying to tell us.

    As you point out, these flame retardants are in a seriously nasty class of chemicals--persistant, toxic at low doses, right up there with PCBs, dioxin. Their use in furniture and baby clothing has been linked to all kinds of harm, including sudden infant death syndrome, but that didn't get much press either. The history of their development is also interesting: the wide use of these chemicals in furniture and carpeting was originally encouraged by the cigarette industry-- which was very anxious to avoid negative publicity and liability for fires caused by cigarette smoking. Which didn't cause cancer.

    As contractors we owe it to our clients to make sure we build healthy buildings, and we shouldn't have to sacrifice our own health in order to do that. But here the US that's a tough proposition, because the building products industry has long refused to concern itself with anybody's health. So this situation is only the latest chapter in a sordid history that includes lead paint, asbestos, vermiculite, fiberglass, formaldahyde, and dozens of other chemical experiments that make our houses unnecessarily toxic to live in and lead to all sorts of occupational hazards for builders. Somehow we aren't learning from our mistakes.

    Industry's refusal to offer safe alternatives to a product that is toxic to little or no purpose is unsurprising in that context: if they did offer non-FR foam, they would have to admit that the other stuff is somehow bad, and people would start asking uncomfortable questions that would lead to other questions and then where would we be. It's much easier to call it green, ignore known safety issues, and move on; as with cigarettes, denial is more profitable, though extremely expensive in the long run. Until manufacturers are actually required to take responsibility for the safety of their products, this craziness is likely to continue.

    The long term solution, as scientists keep pointing out, is to employ the precautionary principle: instead of presuming the safety of untested products and insisting on proof of harm, we should insist that products be safety tested so that we aren't experimenting on ourselves and, much worse, our children and grand children.

    I don't know what to do in the short term. We have a foam rig even though we hate the stuff, we do try to educate clients about it so they can make an informed decision, and we try to use it only as a last resort. Thanks again for your work on this!

  4. user-2310254 | | #4

    Safer, eco-friendly flame retardant
    Alex. I thought you might be interested in this article from the R&D site.

    Of course, most research efforts don't lead to commercial products, but it's nice to know that someone is trying to find a better way to treat rigid foam.

  5. therealcactus | | #5

    HBCD-free insulation
    DOW is now making their XPS with BLUEDGE, a newer fire retardant that is supposedly less toxic than HBCD. It is now available in the US. But it's still XPS.

    Does anyone know of an EPS product available in the US that does not use HBCD?

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