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Community and Q&A

13 reasons why foam fails?

AdrienneBurt | Posted in Green Products and Materials on

Jetson Green just reprinted some blog content from 475 Home Building Performance, here is the Jetson Green post:
and here is the original from 475:

So, um, are any of these assertions valid? As far as I knew, the only drawback to spray foam (closed cell) was the blowing agent. The chemicals are not great for the environment, but they are encapsulated in the foam itself. I know there is a debate about the benefits/risks/unknowns, but the rest of this list has me scratching my head. Are they talking about closed or open cell foam???

Maybe I should just ignore this, but our clients may read this and we should be prepared to agree or refute these assertions.

Here are the 13 things:
1.) Dangerous toxic ingredients
2.) Irredeemable global warming potential
3.) Unacceptably high fire hazard
4.) Hypersensitive on-site manufacturing
5.) Intolerant of adverse job site conditions
6.) Unhealthy off-gassing
7.) Counterproductive vapor retarder/barrier
8.) Terribly hygrophobic
9.) Weak and unpredictable air control
10.) Inflexible and prone to cracking
11.) Excessive shrinkage
12.) Difficult to identify and repair air leaks
13.) Degrading thermal insulation values

Experts, what do you think?

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  1. GBA Editor
    Martin Holladay | | #1

    Any product can fail if it is installed poorly. Many of the listed problems only occur when an installer makes an error.

    At least one listed problem ("counterproductive vapor retarder") is flat-out wrong, while another ("Weak and unpredictable air control") is laughable, especially if this list scares readers into choosing fiberglass batts.

  2. Expert Member
    Dana Dorsett | | #2

    1) toxicity is relative, and the chemicals involved are NOT a particularly high risk, but riskier than cellulose I s'pose.

    2)Global warming potential is primarily a function of the blowing agents used. It' pretty much a non-issue for open cell foam, and there are some closed cell foams out there that are water -blown, no HFCs, but it's an issue.

    3)The fire hazards is highest during incorrect installation when 2lb foam is applied too thick all at once. Once installed behind ignition barriers the risk isn't very different than with some traditional insulating materials.

    4)Hypersensitive? Not so much. Yes, there are specs to be followed, but it doesn't take a team of rocket scientists with instrumentation to get it right. Most blowing equipment heats the A & B side chemicals to a fairly tight temperature range to get a good mix and consistent results, but even the 2-part non temperature controlled DIY-er kits do OK if the DIYer pays any attention at ALL to the tank temperatures (or floats them in a tub of water in the right temperature range.

    5) See part 4

    6) Off-gassing depends- it's only a health issue if the installer totally screwed up the mix/temp or the occupants have a chemical sensitivity issue. After the first week the quantities detected in the room air in a reasonably ventilated house are way behind other occupant-sourced indoor air pollutants.

    7) Counterproductive vapor retarder is a stackup/design issue- where problems occur it lies at the feet of the architect or builder. Placed correctly in the stackup closed cell foam is VERY productive on moisture control issues.

    8) Hygrophobic is true for closed cell, less true for open cell, but "Terribly" has no meaning. It's terrible only if it's done in such a way as to create a moisture problem (see #7)

    9) Air control is pretty good compared to other insulating materials in cavity fills, but not perfect. Applied over the exterior of sheathing (rather than in stud bays) spray foam can be make important contribution to air tightness. Blaming the cavity foam for the lack of air sealing under the stud plates and elsewhere is just silly.

    10) Flexibility varies- open cell is quite flexible, closed cell is more prone to shrinking and cracking only if it's improperly mixed- where that occurs it's an applicator error issue, not an inherent material problem.

    11) See #10

    12) Foam does NOT make it more difficult to identify or rectify air leaks than any other insulation method.

    13) The initial R of closed cell foam is higher than it's aged value, and it depends on the outgassing rates of the blowing agents involved. It does not degrade toward zero, it asymptotically approaches some value. While people will nit-pick about the time period over which the aged-value is determined, most 2lb foam polyurethane will be well above R5 at 1" thickness many decades hence. Rigid XPS at 2.5lbs density will still test at R4.5/inch in a century, 1.5lb XPS eventually hits 4.2/inch. CO2-blown XPS (the stuff sold in Europe) hits those numbers in weeks rather than decades. Open cell foam and water-blown 2lb foam also hit their stable aged values in weeks, not years or decades. It's still a non-zero number, and a very decent number, so?

    To be clear, I'm not a big fan of spray foam, and find some of the industry claims excessive (though they're still playing catch-up with the all smoke & mirrors "reflective insulation" crowd :-) ), but a cheap shot list of throw-away arguments based on false assumptions or worst case installation scenarios can't be taken too seriously either.

    Spray foam insulation is neither panacea nor poison, but use should be judicious, well considered by the builders/designers. And installers need to be both trained and bonded.

  3. Expert Member
    ARMANDO COBO | | #3

    Really???...I wonder if 475 are biased and have an interest in selling their products... Totally distorted and over the top statements like that, looses credibility in what they are trying to achieve.

  4. wjrobinson | | #4

    The sky is falling

  5. Ken Levenson | | #5

    I think some context would be useful before declaring something right or wrong or otherwise. As the introductory post notes, each subject will be discussed, giving it context, in the coming weeks. It will make for an interesting discussion - a long overdue, useful and constructive discussion. We've only got #1 up so far (see ). Hoping to get #2 up shortly.
    All best,

  6. GBA Editor
    Martin Holladay | | #6

    Of course, I'll give you the benefit of the doubt and address each essay as it is written and published.

    Concerning your first essay, I think your language is alarmist, absolutist, and inconsistent. If you want to live a life that is absolutist concerning ingredients -- avoiding plastics and products made with nasty chemicals -- you don't get to use an iPhone, or a laptop, or a car. You don't get to use an airplane.

    It's possible to live that way; I tried for many years. But I doubt whether you are being consistent.

  7. Ken Levenson | | #7

    Martin, Whenever flying, driving and loading up on techno gadgets are sold as "green/sustainable living", they deserve the same ridicule. Cheers, Ken

  8. GBA Editor
    Martin Holladay | | #8

    OK, good -- you are aiming for consistency. That's fine. I'm a certified veteran of that movement. This is what I did: lived in the woods, grew my own potatoes, ate out of a wooden bowl, ground my flour with a hand mill, washed all my clothes by hand in the kitchen sink, cut my own firewood with a bow saw, built a stone cellar, cut down the trees to make posts and joists. I hitchhiked when necessary, because that way I wasn't buying the gasoline. Been there -- done that.

    Have you looked into copper mining lately? It's nasty. Yet copper wiring is incredibly useful.

    Good luck, Ken. It's a noble path.

  9. AdrienneBurt | | #9

    Thanks for all the feedback, everyone. To be honest, I would have just dismissed this list had it not been posted on Jetson Green. In our architecture practice, we still specify closed cell spray foam because we truly think the benefits outweigh the negatives (at least for our climate in Downeast Maine). There are several very experienced installers in our area and we are confident that it is being properly installed. We have Building Green's report on insulation (it's worth every penny) If you're trying to talk to clients about the choices, it's a good tool to have.

  10. Ken Levenson | | #10

    Huh? Please, no straw men.
    I'm not proposing an ascetic life, just more disclosure and honesty in advertising. (and not incidentally, continually working toward being more a part of the solution than the problem.) With insulation, we have choices.

  11. GBA Editor
    Martin Holladay | | #11

    My guess is that if I had a chance to visit your home, I would find many objects made of plastic, and my guess is that you often use products that require electricity.

    I'm not setting up a straw man. I'm stating a fact: we are surrounded by materials which create negative environmental impacts when they are manufactured.

    Of course we have an obligation to protect workers' health. Of course we have an obligation to advocate in favor of new products and processes that reduce negative environmental impacts. But let's be consistent.

    Banning one building product, or labeling it "toxic," is an unsophisticated way to approach these issues. Flat-out avoidance of plastics is extremely tough. I can assure you that when I was an idealistic 20-year-old, I tried to live a life without plastic. It's not a "straw man" argument, because I took the issue so seriously, for years, that I lived out a Thoreau-like experiment in the woods that was based on your ideology.

    If you want to address every single building material with the same approach, of course, you can. It's possible to build a house with stone, mud, timber, and wooden pegs. Many of my friends came very close to succeeding at this quest.

  12. Ken Levenson | | #12

    I'm not proposing a ban on foam. (strawman)
    I'm suggesting we consider it completely, and consider alternatives - that folks can choose effective alternatives that are more sustainable.

  13. GBA Editor
    Martin Holladay | | #13

    Your most recent comment is entirely reasonable, and I agree with your sentiments completely.

    However, you might want to tone down the anti-foam rhetoric a little if you want to appear more reasonable.

    Your wrote: "The chemical companies selling polyurethane foam as green and sustainable, demonstrate chutzpah second only to that of the tobacco and coal industries ... we’re effectively poisoning ourselves ... Kick the foam habit."

    I don't think that, in the vast majority of homes with spray foam insulation, there is any evidence than occupants are being poisoned. Nor do I feel that it's necessary for green builders to "kick the foam habit." And spray foam is significantly more socially useful than tobacco.

  14. user-1081937 | | #14


    Since this is Green Building Adviser, not Energy Performance Adviser I think that looking really hard at the environmental footprint of foam is critical. Since you have the bully pulpit it would be helpful if you were less hostile to different points of view regarding green building. I for one am a bit sick of seeing this much inherently unhealthy material swallow up our buildings as we inevitably call for ever higher amounts of insulation. Now that passive house is burying 12-16-20 inches of it underground many in the PH community are looking for alternatives.

    Sure there is the precautionary principle and we certainly do not know all the long term health effects of such complex chemistry in our buildings and in us but "green" building is generational thinking and I don't want to leave mountains of inevitable toxic garbage for others to have to deal with. If the material is a one way trip to a landfill at best then we should be thinking how we can do better. Open the que for healthy "through and through" high performing building for America.

  15. GBA Editor
    Martin Holladay | | #15

    I'm a big fan of cellulose insulation, which anyone who reads GBA regularly will realize. In most new homes, the best way to build a high-R wall is to build a double-stud wall and insulate it with cellulose. The best ceiling insulation is a deep layer of cellulose on the floor of a ventilated attic.

    That said, there are many retrofit applications and air-sealing applications where spray polyurethane foam is an excellent solution that will help reduce energy use for decades to come. The energy savings achieved by spray foam, judiciously used, are valuable. Many open-cell foams have benign blowing agents, and manufacturers of closed-cell foams are beginning to introduce new blowing agents that don't have the high global warming potential of the current generation of blowing agents.

    Every time we build a home, we use materials that injure the environment. That damage begins when the Ready-Mix truck starts delivering concrete to the waiting foundation forms, and it continues through all stages of construction. Environmental damage occurs when a roofer installs peel-and-stick membrane, when the plumber installs PEX tubing, and when the electrician runs Romex.

    We all need to be conscious of this environmental damage, and do what we can to limit it. That responsibility begins with every construction decision.

    The best house is the one that never gets built. Since we builders are all sinners, we have to learn how to commit small sins instead of big ones.

  16. user-1081937 | | #16


    100lbs of PEX or peel-and stick is many degrees less egregious to a ton or more of foam per living unit. It is an industry bias that foam is the first and best option, and in Europe it is not. An entire retrofit industry exist there that does not depend on foam technology to button up a house. Sure there is a lot of CO2 from concrete but the material is not a toxin at the end of its life.

    Cellulose is only the tip of the iceburg in better insulation products and methodologies that do not depend on exotic chemistries.

  17. GBA Editor
    Martin Holladay | | #17

    I don't have the skills to determine whether 100 pounds of PEX and peel-and-stick is more or less "egregious" than a ton of spray foam, and I think it's fair to say than any environmentalist who claims that he or she can make such a calculation should be viewed with suspicion.

    The current generation of closed-cell foam has objectionable blowing agents. GBA (along with our friends at Environmental Building News) has been in the forefront of reporting on these issues. The problems with the current generation of blowing agents is one reason that I usually recommend the use of cellulose -- which is why your reference to a "ton" of spray foam is a little far-fetched.

    When I recommend that builders consider air-sealing their rim joists with spray foam, the job can be performed with a two-component kit that I can lift with one hand. It weighs considerably less than a ton.

    These are not black-and-white issues. Many wealthy homeowners puff out their chests at their new $700,000 green home, and are proud of the fact that it doesn't contain any spray foam, when in fact the entire project may be an environmental disaster from start to finish.

    If you compare such a project to that of a low-income homeowner who uses a two-component spray foam kit to air seal his rim joists, and thereby keeps his family warm and lowers his fuel bill, there is no comparison.

    This is not a moral issue that has clear lines. All of these decisions are complicated, and any "green" builder who pretends that these are black-and-white decisions is being simplistic.

  18. user-1081937 | | #18


    Sorry what are we talking about? Toxicty, GWP, flash-and-batt, air sealing, whole house 6 inch foam wrap, vapor profile. In the end if I can spec a project that performs as well or better without foam at a similar price I will do it. We can slice this conversation into any size but the direction is clear to me, the less foam the better for the inherent environmental hazards it has. The precautionary principle is alive and well.

    A yes a 'ton' of foam is reference to GBA's many wall details with 4-8 inches of the stuff wrapped around a house.

  19. GBA Editor
    Martin Holladay | | #19

    Adrienne Burt's original question concerned spray foam. Now I realize that Ken Levenson's article appears to paint rigid foam insulation products with the same broad brush -- he is evidently referring not just to spray foam, but also to EPS, XPS, and polyisocyanurate.

    That certainly complicates the discussion. I don't know of any way to write an essay (as Ken has apparently tried to do) to address the environmental effects of such different materials without discussing each material separately.

    If Ken's bottom line is the same -- "we’re effectively poisoning ourselves ... Kick the foam habit" -- whether the product is open-cell spray foam, closed-cell spray foam, EPS, XPS, or polyisocyanurate, here's my reaction: "Whoa. Slow down, Ken. Let's take these products one at a time."

    And Andrew, if your contention is the same -- that polyisocyanurate should be condemned with the same cannon volley used to bring down closed-cell spray foam -- I can only ask, Why? Do you honestly believe that we are "poisoning ourselves" when we install a 2-inch layer of polyiso on the exterior side of our walls?

  20. user-1081937 | | #20


    Yes, I am saying 2 inches of the yellow stuff is nowhere near preferable to rockwool board, fiberboard,cork, etc. All these alternative are (much) more expensive, and hardly available at your local orange store. I think its worthy to change that simply because we know the fire retardants are a very real negative, and there are other issue we don't have a good grasp on. I think the chemistry is simply overly complex for a 50+ year building considering the amount of foam proposed. And when the building is torn down do our grandkids simply ship it to the dump?

    The only drawback to spray foam is most of those things on Ken's list.

  21. GBA Editor
    Martin Holladay | | #21

    Fair enough. You have your preferences; so do I.

    My personal preference is for cellulose. You mention rockwool, fiberboard, and cork. Fine. Let a hundred flowers bloom. (Although frankly, I think the current explosion in interest in cork is silly. But that's a side issue.)

    Here's what I am urging anyone giving green building advice to do: to be fair, to be rational, and not to exaggerate. I think there are some legitimate uses of spray foam; it sounds like you and Ken do not. (I don't know how much weatherization work either of you have done, or how many hours you have spent in attics trying to seal air leaks.)

    Saying that we are "poisoning ourselves" by the use of all types of foam -- including open-cell spray foam, closed-cell spray foam, EPS, XPS, and polyiso -- is an exaggeration and a disservice to the green building community.

  22. Expert Member
    ARMANDO COBO | | #22

    Apparently Ken and Andrew do not get the point. Reading the 475 website, it says: “If we are to address our concerns of health, climate change, safety, energy efficiency, resiliency and reliability, then we ask you to seriously consider eliminating foam from your next high performance building enclosure. Why should you contemplate a foam free enclosure? Because foam fails.”
    Those are statements of fact, as if all foam products and all applications will fail, and that is far from the truth. Those statements without a better clarification up front can turn people off and totally loose credibility with other good work they maybe doing. People may not go back for reference in future blogs. Those statements were made to inflame conversation and drive traffic through their website; and they may have succeeded. Congratulations… and shame on you! Biased, alarmist and flamed statements are not the right way to educate people.
    Most products we use to build homes, if installed incorrect or if used for the wrong application, can result in failure. I specify rigid foam sheets for outsulation to reduce thermal bridging and possible condensation. I also specify cellulose for wall cavities, and open cell foam on the floor truss rim to seal the cavity and avoid most installation problems. A combination of all these insulations offers performance and value to my clients.

  23. Expert Member
    MALCOLM TAYLOR | | #23

    Armando, Do you, or does anyone, know what happened to the 8" of foam which failed after a short period and was removed from Building Science's office walls and roof several years ago?

  24. Expert Member
    ARMANDO COBO | | #24

    Yes, I do. The first remodel had installation of a single layer of 8” EPS sealed with mastic that shrunk and formed many holes, a plastic air barrier with too many holes, plus a 1x4 rain screen and wood siding (I think) with paint. Add to that a couple of bad water management details, some ants in a moist area, and that created a few problems. In other words, product selection, details and installation practices failed.
    The new remodel finished a year a go, was done with taped and sealed multi-layer of staggered-seam polyiso and peel-n-stick air barrier, 1x4 rain screens and cement siding (I think), plus better moisture management detail and installation.
    Goes to prove that even the most knowledgeable and experienced fellow can learn a few tricks…note I didn’t call Joe an Old Dog!!!

  25. user-757117 | | #25

    I think you have the assembly right, but you didn't mention if you knew where the original EPS went - my guess is... a landfill.

    Those are statements of fact, as if all foam products and all applications will fail, and that is far from the truth.

    Every day, much of what you hear and read is misconception, half-truth or outright lie.
    Why pick on Ken?
    His concerns about foam insulation products are legitimate, even if he expresses them in a somewhat sensational way.

  26. Expert Member
    ARMANDO COBO | | #26

    I don’t know what happened to the ESP, but I do know that part of the original renovation at Joe's place was done with XPS and Tyvek, and those assemblies were in good shape after 15 or 20 years.
    I'm not picking on Ken; I do have a problem with the way his article was written. Ken says: "In future blog posts (linked above as we go) we’ll explore the INHERENT FAILURES of foam”. First, some people may not comeback to read his blog, or JetsonGreen or the GBA, and that is unfair representation; and second, it assumes or implies that all foam fails regardless of selection, application and installation; and I disagree with that too.
    One last thought, if Ken or anyone writes in a public blog, the writer should expect to find readers that do not agree with their statements, and someone may ask for more information to back up those statements. I don’t disagree that some of his stated issues can happen, but they may happen under certain conditions, not inherently. In case you didn't notice, Martin and Dana appear to have similar issues.

  27. Expert Member
    MALCOLM TAYLOR | | #27

    Andrew, whatever the original intent GBA has become the Energy Performance Advisor. I find it very useful a such but look for information on Green Building elsewhere. Sure there is a party line here and it is presented as The Way rather than one of several equally valid ways, but you just have to look past that.

  28. user-1081937 | | #28


    Martin and I are fellow sustainable building bloggers (a rarefied species), I'm just poking the egg yoke :)

  29. GBA Editor
    Martin Holladay | | #29

    You wrote, "Sure there is a party line here and it is presented as The Way rather than one of several equally valid ways."

    It seems to me that your sentence describes Ken Levenson's blog, not mine. I'm delighted to describe and highlight a variety of insulation approaches -- not The Way, but The Many Ways.

    There is no single way to insulate a wall or ceiling; that's my point. For some jobs, in some climates, spray foam is a very useful product. For most jobs, in most climates, it's unnecessary.

    GBA is a forum for green builders. We don't all agree, but I want to leave the door open to everybody. I'm not ready yet to ostracize those who use spray foam.

  30. user-757117 | | #30

    In case you didn't notice, I haven't actually laid out my own position in this thread.
    For you to imply that I am in disagreement with anyone on the issue at hand is, at this point, just an assumption on your part.

    I am questioning whether your apparent indignation with Ken's blog post is actually warranted considering your own propensity towards exaggeration - I think you may be taking Ken's use of the word "fail" too literally and somehow I think GBA and JetsonGreen will be just fine.

  31. Expert Member
    MALCOLM TAYLOR | | #31

    Martin, my observation concerned the consensus opinion here on GBA not your moderation or blogs which I value and and find incredibly useful.. For better or worse the acolyte of choice here is Building Science and to a lesser extent Passivhaus, and their approach to envelope construction favouring foam holds sway. Their approach has become the new orthodoxy here, although among the larger building community not everyone is as comfortable with it, or believes that the concentration on a purely engineered approach concentrating on envelope design represents the best way to a green future.

  32. GBA Editor
    Martin Holladay | | #32

    Thanks for the feedback. As far as I'm concerned, all voices are welcome. I even published a blog a while back on straw bale construction.

    We'll do our best to provide a forum for a wide variety of approaches to green building. We are always on the lookout for guest blogs. Send your submissions directly to me: martin [at] greenbuildingadvisor [dot] com.

  33. user-1140531 | | #33

    What about items #10 and 11?

  34. GBA Editor
    Martin Holladay | | #34

    Ken (the author of the list) suggested that we shouldn't discuss the points until the individual essays are posted.

  35. user-788447 | | #35

    I currently work for a business whose primary revenue is through spray foam install.
    I'm still an overall critic of spray foam but I've come to have strong personal relationships with people whose primary income (like mine at this moment) is installing spray foam.

    There are better ways to build. Spray foam is only advantageous because homes continue to be designed without consideration of detailing the thermal envelope. Spray foam does not make an overall good air barrier, especially in custom homes where spray foam is mostly used, because it is located between structural member and hence its compromised thermal performance contribution.

    Yes the retrofit market is different. I often spec spray foam for retrofits.

    Spray foam install has so many variables and therefore more opportunities for mistakes to happen. I have family in other trades and I belief I've seen the impacts of chemical exposures on men as they age. Anecdotally, I often go home from work with a feeling in my throat that I've smoked cigarettes after being exposed to the spray foam barrels in our warehouse.

    Again God bless conscientious spray foam installers and the business' that strive to be responsible. But it makes more sense to me from a building performance and environmental standpoint to DESIGN buildings that use the sheathing layer as the air barrier and have the most the thermal resistance value outboard the sheathing in the form of rigid insulation boards that are manufactured under controlled conditions.

    In my opinion if you design buildings and RELY on spray foam between structural members as your building performance strategy you are not as great a designer as you could be.

  36. Expert Member
    MALCOLM TAYLOR | | #36

    J. Chesnut. Very well put.

  37. user-757117 | | #37

    J Chesnut,
    I haven't seen you posting here in a while.
    Thanks for sharing your thoughts.

  38. homedesign | | #38

    "Another turning point.... a Fork stuck in the road..."

    I agree with those who are taking the Not-So-Foamy Road

  39. albertrooks | | #39

    Ron & Martin,

    Not to make light of the situation, but I often feel like I'm suffering from #10 & 11 myself. My wife complains to me of #9, which she is concerned will lead to #6.

    Nice job Ken. Pave the way for an active discussion.

  40. user-1090662 | | #40

    Here's my homeowner-retrofit perspective: I see some of where Andrew Michler is coming from with his "ton of foam" argument - in my case a ceiling and wall retrofit calls for some 600 lbs and it's not an easy decision. But it feels hard or impossible for me to connect with real world contractors who have alternatives to foam, for areas of my home that have low slope roof or other difficulties. Sometimes it seems contractors and code officials would be happiest if I tear half the house down and create 10 tons of debris - think of the embedded energy in a replacement.

    Andrew wrote above "It is an industry bias that foam is the first and best option, and in Europe it is not. An entire retrofit industry exist there that does not depend on foam technology to button up a house." What would contractors do if my house was in Europe? Maybe, membrane over mineral wool? As far as I can tell, that would be a costly commercial install in N. California. In fact even for exterior foam more than a couple of inches thick, I see no able and willing installers. What I see is a lot of homes, expensive and not, with poor insulation. I have to consider the closed-cell interior-insulation option seriously - I'm looking for another game in town but it seems the only one.

    Dana Dorsett wrote "And installers need to be both trained and bonded." Props to Dana. I will check that foam bidders are bonded.

  41. GBA Editor
    Martin Holladay | | #41

    Ken has written an essay to defend Reason #2 on his list:
    Reason Foam Fails #2: Unacceptable Fire Hazard

  42. wjrobinson | | #42

    Albert Rooks, thanks for the chuckles me gets everytimevi open this thread. B-)

  43. albertrooks | | #43

    Moving it back up.

    From the stand point of fire... I have to agree with Ken that foam is the poorest choice one can make. Mineral Wool, Cork, Woodfibre insulation boards all have far longer burn through times (MW is fire resistant) than any of the foam boards.

  44. heinblod | | #44

    Mineralwool as such is not combustable......

    .....BUT the binder, the glue holding the individual fibres together frequently is.The resin acts like the wax in the candle, the mineralfibre being the wick.

    Even if the binder is non-organic the surounding matter would feed the combustion.For example the wind break membrane, the breather membrane, moisture barrier and so on.
    Hot organic gases make the candle burn.

    There are many cases of mineralwool fibre fires reported.

    Some samples, here one from Berlin/Germany:

    Here one from Linz/Austria:

    Here one from Wiesbaden/Hessia/Germany:

    And it does not need an organic matter in or near the mineral fibres at all, they themself can act as a catalyst and 'split' the air if hot air/gas passes through it .
    But for the catalytic potential of mineral fibres better contact a physican or chemist.

    The fire in Roubaix/France was indeed a mineral wool fire, the small amount of wind break material itself had only a small heating/thermal capacity. It was the catalytic effect of the mineral wool which turned the fascade into a blaze.


    Here another foam fire from Sweden, the fire broke out in an apartment, ate throught the insulation up to the roof, over the insulated roof down on the other sides of the structure:

    Mineralwool has the advantage that it doesn't drop, does not act like napalm or petrol. But it burns as well if fed.
    If using mineral wool bats/mats use the types bonded with mineralic binder. Not the cheaper product with resin based binder.
    Avoid all potential 'feeding of the candle', opt for a tested building system

    ( )

    and not for an uncertified DIY method.

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