Eelgrass Insulation

Just got this from Germany. I don’t know about fire or vermin hazard, but it looks like it was used extensively at one time.

“An insulating material consisting of dried eelgrass held between layers of cloth or paper; once used as thermal insulation, now little used.

Read more:

dear mr. kahn,

we love your books, they are great inspiration for us.

we want to ask you: have you ever experienced insulating houses with eelgrass?

we are great fans of eelgrass, it is possible to collect it from the coasts almost all over the world. in danmark and in some other countries there are roofs thatched with eelgrass/seagrass, they protect the houses for several centuries.

   we just started to deal with it in germany and would like to pass on the impulse to other countries because it is such a wonderful material and we don`t know any other insulating material which is as ecological as eelgrass.

to get an impression you can take a look at our homepage:,

   it is funny: we found in the internet an advertising of cabot`s quilt from boston in the year 1912/1926. there is much information in it which is relevant to our days, too. for example: in the plant is much silicate, this has the effect that it doesn`t rot and it doesn`t burn.

we hope we aroused your curiosity now.

best regards,

swantje and joer”

About Lloyd Kahn

Lloyd Kahn started building his own home in the early '60s and went on to publish books showing homeowners how they could build their own homes with their own hands. He got his start in publishing by working as the shelter editor of the Whole Earth Catalog with Stewart Brand in the late '60s. He has since authored six highly-graphic books on homemade building, all of which are interrelated. The books, "The Shelter Library Of Building Books," include Shelter, Shelter II (1978), Home Work (2004), Builders of the Pacific Coast (2008), Tiny Homes (2012), and Tiny Homes on the Move (2014). Lloyd operates from Northern California studio built of recycled lumber, set in the midst of a vegetable garden, and hooked into the world via five Mac computers. You can check out videos (one with over 450,000 views) on Lloyd by doing a search on YouTube:

19 Responses to Eelgrass Insulation

  1. Eelgrass was used fairly commonly as insulation in the 19th and early 20th centuries on Cape Cod (and likely before as well).

    It came to be seen – maybe wrongly – as a fire hazard, though. In George Howe Colt's excellent book about his family's 1903 Cape summer house, The Big House, for example, he reports that a combination of aging wiring, balloon framing, and eelgrass insulation were viewed as having caused many houses of that vintage to burn to the ground there.

  2. bit off the topic, but since it is insulation, maybe not. Have wondered about something,maybe someone has an idea… Nothing am doing, just some idle thinking.

    a) if a person made a solid log/house with thick enough walls, does that accomplish significant insulation value?
    b) if a person made a regular sort of house with, say, two foot thick walls, and regular plaster board on inside/regular wood siding on outside, would that accomplish significant insulation, so that very little would be needed inside to heat the house?

    just a couple of things have wondered about for yrs,if anyone has any idea.

  3. hi Swantje and Joer, via lloyd
    i don't understand, do you mean : destroying these precious sea meadows ? what grass are you talking about, eelgrass and sea grass (botanic names = zostera marina, zostera noltii) ?
    perhaps they grow in abundance on german coasts and you can harvest it without damage ?
    but they don't on the Atlantic or Mediterranean coasts where sea meadows are regarded by scientists as natural and fragile treasures.
    From Wikipedia : ''zostera beds are important for sediment deposition, substrate stabilization and as nursery grounds for many species''.
    Sea meadows feed thousands of birds as brant geese (branta bernicla) and eurasian wigeons (anas penelope).
    in my region (Golfe du Morbihan, west of France) the winter population of brant geese has decreased from 30 000 to 15 000 birds, in the last 15 years – because of the loss of sea meadows.
    please, don't harvest them for insulation !
    sorry, i do prefer hemp, bulk or blocks, for high performance new insulation materials.

  4. hi,

    we wish to protect and respect nature as much as you do. don`t worry, we are talking about something really ecological.
    if you take a look at our homepage you can see fotos of zostera marina that is brought by the waves up to the shore. we don`t have many kilometers of coast, but every autumn/winter there are several thousands of tonnes of seaweed that have to be carried away.
    it is not harvested by people from out of the water, the plant renews every year by nature. the big heaps of old seegrass are not nice for tourists and the people who collect it regard it as waste.
    if you take a look at wikipedia "eelgrass" you can find a map of the world with indication of where is how much of it.
    here we find it in mostly on the coast of the baltic sea (east cost), maybe the current brings it away from the french west coast. but you can also google for neptutherm, i think it is from the mediterranian sea.
    so, with deep love for nature, greetings from germany to france,
    swantje & joern

  5. Eelgrass is mainly composed from silica (same like glas and sand), it makes eelgrass fire- and also vermin resistant by nature. The eelgrass we use was layed out on meadows so that rain and sun affected it: the salt of the seawater is washed off and it is a bit softer. It is good to wash off the salt because salt is hygroscopic, it attracts water. Other nature insulation materials and also isofloc (newspaper) are often treated with Bohr-salt against fire and vermin.

    A historical brochure about Cabot`s Quilt (1928): >Cabot's Quilt is a real Fire Retardant. It has saved many buildings from destruction by fire, for the Zostera Marina of which it is made, being a sea plant, is composed mainly of non-combustible silica. Insulators made of land plants or their fibers or of the bark of trees like cork are composed principally of carbon, and burn freely…<

    We think that the seagrass insulated houses that are mentioned in the first comment could burn down despite of seagrass because it was a thin layer of seagrass between two layers of paper in wooden houses.


    Concerning the insulation questions above we`ll try to answer tomorrow!

  6. Joern Hartje, that is interesting about Eelgrass Composition. Guess if the layers (to sandwhich the grass) were made of woven Eelgrass, this might add fire resistance, as well as further insulation value.

    Seems like it would be non toxic and non allergic.

    Will be interested to your answer to insulation value of Eelgrass.

  7. Interesting Link re Eelgrass
    Lots more there than this, but
    •Radio City Music Hall and Rockefeller Center in New York were built with eelgrass insulation due to its excellent insulating and sound proofing qualities as well as its non-flammable nature. Early historical records indicate that in the United States eelgrass brought $20 to $30 a ton as insulation and sound-deadening material. One study indicated that a six-inch layer of eelgrass spread to a density of 1.5 pounds per square foot has the insulation efficiency of six inches of fiberglass insulation. Further studies reveal that Zostera will burn if subjected to a flame but will not support combustion by itself.

  8. It is very nice to see so much new information!

    Now we try to answer the questions from the person who wrote on February 8, 2013 at 8:02 PM:

    Stone/clay and other massive materials are really good for accumulation warmth, but they also give it back to the room and also to outside.
    If you have thick walls you need a long time to heat these walls up, even if you have thick walls they didn´t have much insulation capacity. If you have an old house and you can´t insulate you can install a heating system inside the wall (put it in clay), this would make the wall more dry and this would explore the insulation effect…
    In summer stone walls can accumulate the warmth from the sun. Because of this some people build walls of different materials to south and north.
    Wood is a good compromise between accumulation warmth and also insulating, but it might be quite expensive.
    All together this calculation is for sure complicated, bit theorie and depends on many factors.

    In German you can find online calculation tool: I guess there will be something alike in English language in the world wide web.

    Sorry for language difficulties, hope you got what I wanted to say!

    If you have further questions please contact me.


  9. Curiosity aroused, inner nerd released… A few more U.S. google results below:

    Cornell University general overview of eelgrass:

    Historic New England – house from 1683 using 'modern' eelgrass insulation rather than traditional "clay nogging"(makes me reconsider that "bump on the noggin" saying):

    Colonial Williamsburg – reconstruction blog – Although their buildings had clay "nogging" x, there's some discussion of eelgrass & other older construction materials. The Wmburg experts say the R-value of eelgrass was negligible:

    Old House Journal – article from 1992 on preexisting insulation:

    Description of history of Cabot's stain (still sold) and Cabot's Quilt insulation. ( states that the founder 'had one mission – to preserve wood'. Which is a shame, since it gives him short shrift & indicates you won't get any eelgrass info from them…):

    Woman living in old house with Cabot's eelgrass insulation seems impressed with its romantic history, but not with its insulating properties:

    Fables of the Deconstruction – Wall of Cabot's Quilt eelgrass insulation (taken during "de-construction", as opposed to demolishment):

    Newspaper interview with hippie 😉 in 1979 wanting to restart the eelgrass insulation industry. Says NJ paying to haul it away, said it was also used to pack bananas, line coffins & fill matresses since it repelled pests:,2615150

    Many thanks Joern & Swantje for the fascinating reading. Here in Seattle when they say "obviously solar won't work", we just tell them to look at German weather, lol…

  10. Another Natural … renewable…

    Cannabis Construction: Entrepreneurs Use Hemp in Home Building

    solution he has come up with is not some space-age polymer or recycled composite but a material that has been in use for millenniums, though it is more often demonized than venerated on these shores.

    Savage is hoping to put hemp to use not in joints but between joists

    ((( pardon my inexperience here…but what happens when these hemp houses go up in smoke…."free high"?

    oh…and all those B.C. fires….are the good folks there less stressed over it all, cause they are getting a few whiffs of burning fields of pot?)))

  11. HI just searching internst for Eelgrass insulation and came across your page. I work for local council in London, England and some old housing or apartment blocks as you'd say have Eelgrass insulation in the loft spaces. Some you can still make out the Cabot's Quilt on paper lining. I even foud a paper bag of tacks in a loft especially for fixing Cabot's Quilt. I'll post a snap on Flickr soon. Thanks Duncan

  12. Just bought an old farmhouse in New Hampshire and found Cabot's Quilt Insulation in the attic. It does seem to be vermin and rot proof. It must be a hundred years old, and is still up there. It hasn't rotted away and though the mice have gotten most of the corn cobs that also insulated these walls, it doesn't look like they've gone after the eelgrass. I can't speak to the R value, because overall the house is poorly insulated.

  13. Hi Lloyd,
    ran accross this on a free site, and curious if it could be/is used for insulation. Seems like it should be good for something.

    FREE Hemp Fiber

    FREE hemp fiber for pick up in Calgary. Several truck loads available. The fiber is a co-product stream from hemp processing, produced from Alberta grown hemp; contains long hemp fiber with some hurd. Potential use – for animal bedding, ground covering/mulch.

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