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Thoughts on Knauf Ecoseal

pJWGZu8ebo | Posted in Green Products and Materials on

Hi all, I’m building a modern house in Seattle ( We’re considering upgrading our insulation from standard batt, and one of the most-effective proposals is a very new system by Knauf, called Ecoseal ( It seems to be an elastomeric glue that is sprayed into all joints for airtightness; then standard batts are used after that. Anyone have any thoughts? It sounds good, but I’m wary of choosing a totally new and untested product.

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  1. Riversong | | #1

    "Standard batt" is hardly the place to start, since it's the most poorly-performing of all common insulation materials or methods. And Knauf's KISS system uses their proprietary EcoBatt, which is a modestly eco-friendlier fiberglass that appears to be coarser than conventional batts and probably harder to fit neatly.

    It's just another variation on "flash & batt" or "flash and fill".

    Air sealing is necessary with any low-density fibrous insulation, but you can do the same with a caulk gun or foam gun, or use the air-tight drywall system with an elastomeric caulk like Tremco. I imagine their proprietary system ain't cheap and requires a factory-certified installer.

    Blown cellulose in a 2x6 wall should be the minimum baseline for any responsible construction. There are myriad ways to upgrade from there. If you must use batts, then use recycled blue jean batts with borate fire retardant (the same that's in good-quality cellulose).

  2. Interested Onlooker | | #2

    Blog link not working for me.

  3. anon | | #3 is the correct website (not phinny)

    with all the windows, are you looking at upgrading glazing as well? slightly upgrading the insulation while leaving horrible glass and frames isn't a recipe for success. i'm surprised you aren't running this by Pb - are issues of energy/air sealing and weatherproofing still not top priorities?

  4. pJWGZu8ebo | | #4

    All the windows are double-paned Argon filled, and at most U-.35 (and often better). It doesn't look like we can get much better without going to vinyl or fiberglass, which wouldn't fit the aesthetic. Pb and our GC are aware of all the options we are considering, but I wanted to get more opinions.

  5. skylarswinford | | #5

    This product is nothing but "Lipstick on a pig". Steer clear of fiberglass, especially batts. Have you thought about taping the exterior sheathing for your air barrier? Let me know if you would like more information about this process. I would recommend cellulose in the wall cavity, preferably wall-spray if you can find a qualified contractor that doesn't over hydrate the material during install. I would go with 6-8 inches of low density spray foam at the rim joists. What are you planning for your foundation and roof system?

  6. Riversong | | #6


    Tape is not a long-term solution for anything. Cellulose functions best in a wall that can breathe, and taping sheathing undermines this. And open cell foam at the rim joists will result in condensation at the rims - closed cell is required.

  7. pJWGZu8ebo | | #7

    I'll add a few thoughts. My understanding is that the Vaproshield manufacturers do not recommend taping horizontal seams for an air barrier in marine environments like Seattle, since it impedes moisture leaving the building interior. Our closed cell foam bid came in literally 6 times batt insulation, so there's no way we can afford it. The six insulation companies in Seattle our GC got bids from have all stopped doing Cellulose, again because of moisture issues in Seattle.

  8. GBA Editor
    Martin Holladay | | #8

    That's another example of regional variations in building practices. Many areas in the Northeast are quite damp and regularly experience heavy rainfall, but cellulose is an accepted insulation material here. The suspicious attitude of Seattle contractors toward cellulose is surprising.

  9. David Meiland | | #9

    I know at least a couple of insulators here (an hour north of Seattle) who blow cellulose but apparently it costs more than shredded FG. Nonetheless it's fairly common, and as far as I can tell it's actually fairly dry here, unless your house is deep in a towering cedar forest.

  10. skylarswinford | | #10


    I can only speak for my inter-mountain climate with 9000+ HDD days, but in my experience your generalizations regarding low density foam are wrong. Trust me, you are the last person I want to disagree with. I know I will be in for a treat. I just can't ignore what I have seen with my own eyes. Real world experience has proven to me that rim-joists sprayed with low density spray foam are condensation free all winter, even in an extreme climate. A rim joist with 6-8 inches of foam is very airtight and the perm rating is 2-3. Unless the home has no ventilation and experiences ultra high winter humidity levels, vapor driven by diffusion simply won't cause condensation issues.

    Speaking to taping the seams. You always seem to praise the hygric buffering capabilities of wood products. Wouldn't any potential moisture buildup at the impermeable seam tape be managed by the surrounding hygric materials? (I'm just hypothesizing on this one, so feel free to interject) Once again, this assembly is airtight and cellulose is a great air retarder. The only moisture should be minimal and only the result of diffusion. Additionally won't the wall be drying inward during Seattle's dry Mediterranean summers?

    Aren't window flashing tapes, including vaproshield's, vapor impermeable? Why the exception for this part of the wall? Of course, if you are really worried about the tape there plenty of vapor permeable ways to seal the seams.

    Can someone explain to me what type of failures Seattle builders have been having with cellulose? If a house has a leaky window flashing the insulation type isn't going to change the outcome much.

    Aseem, I hope we can help you get squared away. I'd hate to see you leaning towards fiberglass batts. Over the long term it will be a very costly decision. Spending a little more upfront on insulation is a wise investment. Now if only we could help you figure out the best system for your budget without confusing you more;) I can help get you in touch with some cellulose contractors in Seattle. Did you say what your roof or foundation system is?

  11. Riversong | | #11


    It's that rim joists are typically exposed in basements, which are often the most humid part of a house. If the basement is dry, then open-cell shouldn't be an issue.

    Wood is an excellent hygric buffer, particularly exposed end-grain, but plywood is to wood like American cheese is to Vermont cheddar, and OSB is to wood like Velveeta is to cheese. Those materials have too much resin to function as real wood.

    Yes, a Seattle house may dry to the inside in summertime, as long as nothing is impeding the vapor diffusion.

    Tape relies on a tenuous adhesive bond that is unlikely to have a 100 year longevity, and all impermeable flashing tapes are problematic in my perspective - just another example of a "solution" that creates more problems then it's intended to solve, particularly when coupled with OSB.

  12. pJWGZu8ebo | | #12

    Hi Skylar, it would be great if you hooked me up with Seattle cellulose contractors, I'm not sure what you mean by foundation and roof "systems", but I can describe them. Our foundation is a concrete-poured slab, and we have rigid insulation on the exterior for any below-grade concrete walls. We have radiant heating in the slab. Our roof is flat and ventilated, built with trusses and covered with a TPO membrane. No attic. Our sheathing is all OSB.

  13. pJWGZu8ebo | | #13

    I'll add one more thought. I want to make the environmentally-conscious choice, but I have trouble seeing how choosing batt would be all that costly. I currently live in a townhouse a mile away from my new house, built in 2005. I'm sure it was built in the cheapest way possible. But my gas bill in the worst month of winter was $2 a day. In the summer it was around $0.75 a day, so I imagine that's what we spend on hot water and cooking. In the end, that means we spend $1.25 a day for the worst month of winter. And that's using a direct-vent fireplace for most of our heating, which I imagine won't compare to our new 95% efficient condensing boiler radiant heat system (though the new house will be bigger and have much bigger windows). From a purely economic perspective, it seems hard to believe that spending thousands extra on blown insulation will be a better financial choice unless my time horizon is VERY long. I'm still interested in better insulation because of the environmental ramifications, but I'm not convinced on the economic side.

  14. Riversong | | #14

    It always comes down to simple dollars and cents.

    Well, if the environmental considerations don't trump short-term cost, you might consider health ramifications.

    Fiberglass is a recognized carcinogen that typically uses formaldehyde-based binders, which is a known chemical sensitizer and the precursor to Multiple Chemical Sensitivity.

    Fiberglass batt insulation can increase the combustibility of a structure, while cellulose dramatically reduces it. Fiberglass insulation is often associated with mold growth, while cellulose has a powerful not toxic mold inhibitor and also effectively redistributes absorbed moisture to limit mold potential in wood framing. Fiberglass insulation typically becomes infested with rodents, riddled with tunnels and speckled with waste and dead bodies. Cellulose with borates (the fire retardant and mold inhibitor) also discourages rodents and kills all common household insects.

    Cellulose buffers extremes of interior humidity, absorbing and releasing up to 30% of its weight in water reversibly, has better sound attenuating qualities than fiberglass, higher R-value and much significantly limits air convection.

    Fiberglass loses R-value when the temperature deviates either above or below room temperature (in other words, when it's most needed), while cellulose actually increases in R-value as it cools.

    So, in summary, cellulose is better for the environment (almost zero embodied energy or global warming contribution, and almost no impact on air or water quality), it performs far better as an insulation, and is far healthier for occupants.

    If it costs a little more, the payback is immediate in health, security and comfort.

  15. David Meiland | | #15

    There is no comparison between batts and blown-in insulation, in terms of filling the gaps and nooks and crannies, no matter how careful the batt installer is. If your GC can't find a good, competitive company to blow in cellulose for you then something's wrong.

    As far as heating your house, I did take a glance at your site when you first posted and I would be surprised if there is not a heat loss calc already done. From your standpoint it's worth knowing who did it and how they did it. It should give you a reasonable projection of how many BTUs you will be buying. There may not be much of a comparison to a townhouse. Your house has a lot more glass, more exterior wall area, more roof, cantilevered floors, etc.

  16. Riversong | | #16

    In fact, that looks like a house geometry intended to maximize heat loss through the envelope.

  17. wjrobinson | | #17

    Aseem, you are right that you Live in a much milder and wetter climate than Martin or Robert. Sealing the cavities when using batts is now preferred if batts are used. Myself, I am a believer in cellulose as Robert is but am also accepting of what you are doing and of external reused foam and many other ways.

    Make your own decision and feel good about it.

    Oh... as to closed cell spray foam. I prefer water blown Icynene and have had no issues with condensation. Break some closed cell and smell it... chemical stink.

  18. Kevin Flynn | | #18

    I have seen the EcoSeal product in person, and it is a tremendous product. Many posters here are not familiar with how environmentally friendly it is along with Knauf's EcoBatts. The batts and Ecoseal are more than 40% post consumer recycled material, and Ecoseal is much more ecofriendly than spray foam. It has very low VOCs and makes for a great barrier for sound and air.
    check out this link

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