There is a consistent myth floating around the internet that common earthbag buildings are naturally super insulating. I don’t know how this idea got started but it has certainly spread widely. I see it written into basic  descriptions of earthbag building on forums and websites frequently, often by folks who would appear to be experts on the topic, lending the myth a degree of false legitimacy.

Let me set the record straight: common earthbags filled with earth are not very good insulators. In fact the R-value of compacted earth is roughly R-1 per foot, so a standard earthbag wall might yield no better than R-2. That is roughly equivalent to a dual pane glass window.

Earthbags filled with earth are excellent providers of thermal mass, which serves an equally important function in a well designed house. Thermal mass has the capability to store heat (or coolness), so a large interior placement of this mass will help stabilize indoor temperatures. But it needs to be insulated from the outdoor environment or it will lose this heat or coolness to the atmosphere.

In some circumstances a solid earthen wall will seem like it is insulating very well, because the interior is comfortably warmer or cooler than outside. This can happen because of the time factor; it takes time for the mass to change its state. In some moderate climates this can help keep an interior space fairly comfortable, as happens with the “flywheel effect” of the mass giving off the heat gathered during the day at night, and then helping to cool the house during the day if the nighttime temperatures are cooler. But this only works well during certain seasons in moderate climates and cannot be counted on in most localities around the globe.

Fortunately earthbags offer the very flexible opportunity of being filled with other materials than earth. I built a very comfortable earthbag house by filling the bags with scoria, a lightweight volcanic stone. Other natural insulating fill materials are rice hulls, perlite or vermiculite. Or you can build a solid earth-filled earthbag wall that has an adjacent insulating layer. In some ways this would yield the best solution, since you still have all of that wonderful thermal mass on the inside.


Comments

The Myth of Earthbag Insulation — 43 Comments

  1. Hi. I live in in a hot humid climate all year long. I want to avoid to thermal mass to send me heat during the night. My question is: for insulating the bags, you think that a combination of cob and tiny rocks insude the bags and also rocks all around the outside plaster could work to make it better? On top of that im putting vents and a risen roof with opening towards where the wind blows.

    Let me know what you think, and thank you for being so helpful, I want to be able to build my house and share my knowledge with people from Guatemala so they can have a possibility to have a house without ridiculous debt :)

    • Both cob and stones, large or small, are also thermal mass and will not help with the needed insulation. A better solution is to find an effective local insulating material that you can use to fill the bags with. If you read the article at http://earthbagbuilding.com/articles/pumice.htm you will notice that some of the very first experiments with earthbags was done in Guatemala and they filled the bags with local pumice. Perhaps you can find a source for this material and use it there.

      • Thank you for the helpful response :)
        One question, the pumice would be added with the cob? I have a clay soil that has 20% expansion and I wonder there would be a problem with that. Or you believe its just better to fill it withouth the cob and use other mix instead?
        Have a nice day :)

  2. Hi Respected Sir,

    I am planing to build small resort in hilly area in India ( Its north part of India , Himachal Pardesh), in the month of dec & jan there is snow aprox 2-3 feet every year. otherwise temperature is between +32 to -7 degree ,Rain also happen almost very frequently in month of July-August.

    Shall be very grateful if you can advice me should i go for earth bag ?? and what kind of roof i should build.
    Looking forward for your valuable inputs.
    Regards
    Harmeet Singh

    • Yes, earthbag is a good choice especially due to the seismic risk. An NGO just built an earthbag in northern India. Maybe I can find the email.

    • Search our blog for gravel bags. This is my preferred foundation method. A typical builder can save thousands of dollars on the foundation alone. Of course, this is only for non-code areas.

  3. How about using just sand in the bags? (Like the kind used for emergency flooding situations) Can you comment on how that would be for long-term stability, resistance to rot, and insulation?

    Thank you!

    • I had a problem with insulating an area that was on a slab. Air was coming in where the slab met the wall. I used tubular sand bags and it has cut out all air flow in the area I had the problem with. 2 years so far. Cheap fix and also no more insects come in.

  4. I am currently purchasing land in Chambers,Az I am interested in The Earthbag building . I may need help but I think I can build this. They look nice.

  5. Hi Everyone,

    Thank you for this site. It is wonderfully informative!

    I have a few questions about building a superadobe dome in Southern New Hampshire.
    One point to mention is that there won’t be any plumbing or electric in the building and the space is going to be 200 square feet(16 foot inside wall diameter) and 14 feet high at the highest point. It is intended to be a meditation hut and resting place for four seasons. There will be a wood burning stove or perhaps a rocket mass heater for warmth. and a few windows for light and ventilation.

    Walls are 21 inch thick earth bag tubes(when filled and tamped) and 10 inches of compressed straw for insulation on the exterior. Plastered, tarred, and plastered again(3 inches of plaster total) over the straw. It will have a stone/gravel base and another 2 inches of plaster on the interior.

    These are the specs I received from the builder and I just want to double check with another source before moving forward with the project. Do you think that this structure will be able to stay warm in the winter? I was told that the R-Value for this structure would be around R-40 but I haven’t found any information that supports this figure. I have read a few things that mention thermal mass can have an amplifying effect on insulation but I’m not familiar enough with the techniques to be sure(hence the questions).

    I greatly appreciate any and all constructive feedback you are kind enough to share.

    Best of Health and Happiness to you all,

    Louis

    • Hi Louis,

      I do think that the hut that you describe will be comfortable in all seasons, with just a bit of extra heat in the winter probably. This is if it is kept at a good living temperature most of the time. If it is left unheated for a long period, it may take awhile for the interior mass to get warm again. But then it is such a small space that with your little wood stove or rocket heater you can quickly get the air to feel comfortable.

      It is hard to evaluate R-values in a wall system like you describe. The actual R-value of the earth and the compacted straw would not add up to R-40, but then the performance of the entire package could perhaps be equivalent to a good straw bale hut that would be R-40.

      • Hi Kelly,

        Thank you very much for responding.

        These were my feelings, but it is nice to have them supported by people with experience in the field. If it works out for this winter, I’ll let you know how it went in the spring.

        Peace be the Journey,

        Louis

        • I’m not sure if this is timely or not. Regardless of insulation value, I would worry about the outer walll, being cold in the winter. There is a great risk of condensation collecting against the surface and possible damage to the straw insulation.

  6. We’re in Southern Illinois getting ready to start building on 40 acres. There doesn’t seem to be any inexpensive suppliers of scoria or other ‘insulating’ materials for an insulated bag. We’re wanting to stick with domed structures to remove the need for traditional roofing.

    Is it possible to mix lava rock and dirt for a hybrid bag? The thought being that the porous rock would add insulating properties to the bag without the expense of it being 100% lava rock.

    Like the other gentleman that asked about spray foam, I too would like to know if this is a viable alternative. I found a supplier of foam insulation but would love some validation as to whether or not it’d work on the outside of an earth bag dome.

    • Domes evolved in deserts. In rainy/snowy climates they’ll have moisture problems. Look into Roofed Domes. (search our blog) Or you can add a rainscreen — a ferrocement layer that floats above the dome if you’re determined to use a dome shape. (also covered on our blog)

      Trying to combine insulation with mass as you describe won’t work.

      Yes, you can use spray foam insulation on earthbag buildings. Just be sure to look into the details and apply it correctly.

  7. Would this work well if you used old tires instead of bags. Obviously you still pack them with you filling medium. If tires would work, what difference in construction would you foresee? Thanks!

    • I’m not a fan of tire building at all. Earthbags are way faster and user friendly. Look to Nepal for example where unskilled villagers are building earthbag walls for schools in 10 days using tubes. It would go even faster except they have to build giant buttresses due to earthquakes.

  8. Would it make sense to build the south wall with earth, no insulation, big hat in front, so that it heats up in the winter and doesn’t get the summer sun, and build the other walls with strawbale? (in addition i’m interested in adding a glass extension on the south part of the house)

    Other question, how would you build the “boots” of a strawbale wall, considering it should be slightly over the ground? make it all gravelbags? put both gravel and then earth bag before straw? Would you insulate those “boots” from the outside? (sorry if the vocabulary doesn’t fit, translating from french).

    Last one : in these conditions, do you feel it’s possible to keep a raw packed earth ground, without any ground insulation (keeping earth’s thermostatic and electric capacities). I keep your advice about the insulating plastic for an underground north wall.

    Living in the middle of France, a bit colder and wetter than our oceanic climate.

    Cheers and thanks for caring

    • The best, most energy efficient methods depends on your climate. Always use climate appropriate design. In your case, south facing windows, scoria bag foundation stacked above grade, straw bale walls on the west, north and east would be good choices. If scoria/lava rock isn’t available then you could use regular gravel with rigid foam insulation on the outside.

      Plastic doesn’t insulate much. It’s primarily a moisture barrier. Build on high ground in wet climates. Raise the building site if necessary to avoid problems. Put a moisture barrier under the floor. Use wide roof overhangs so the walls don’t get wet. Adjust the size of overhangs based on the solar angle.

  9. Hi Owen, I love your site and check it quite frequently. What if the earthbag home is at least partially underground? We live in Michigan where we have long, tough winters and summers can get up to 90+ degrees. Our thought was to build underground, or at least partially underground, for better protection from the elements.
    Thanks for your help and keep up the good work!!

    • Yes, that’s possible. It’s best to build on high ground and add earth berming up to windowsill height, etc. to avoid moisture problems. True underground houses run greater risk of flooding. Add 2-3 layers of heavy duty plastic sheeting between the walls and the earth berm.

  10. The insulation factor has had me puzzled for awhile. Hoping to build earth bag in the southern San Joaquin Valley area, frequently over 100F summer, may not drop below 90 at night. Freezes to low 20’s normally in winter, may reach 0 in winter (quite unusual). So I know we need insulation. Question is: does the spray insulation keep the earth bag from “breathing” and water vapor moving in and out of the house? Read something about using insulation boards made from wood chips (cannot recall the correct name), and then could I cover with chicken wire and earthen plasters? Any advice? I will look up the UCLA site also.

    • The standard method is to apply insulation on the outside of the bags once the walls have thoroughly dried for several months. Use whatever insulation makes sense to you, and then plaster the exterior.

    • Cob or earth plaster provides no insulation. Insulating materials have lots of air spaces.

      Use a search engine to search this site. Look up the term “passive cooling strategies”. There are two blog posts that list dozens of low cost cooling methods that could be used in Texas.

  11. I live in upstate South Carolina. I am very much interest in building a earthbag home. I am wanting to use the least amount of energy on cooling/heating. Just wondering what you would recomend on the building and insulation of a earthbag home. Thanks.

    • Search our blog for details.
      Cooling: search for ‘passive cooling strategies’
      Search for insulated earthbag houses for cold climates.

    • Charlie:

      I highly recommend that you read about and use this FREE software program put out by UCLA.

      http://www.energy-design-tools.aud.ucla.edu/heed/

      That software program will do all the difficult number crunching for you. You load the appropriate climate data for your area, and then you can very easily input various different house designs that you are considering. The software can tell you how much it will cost you to heat/cool the structure.

      This is not a toy. It’s a very powerful program. You can make basic house design decisions for objective reasons, and optimize the design of your home. It will save you boatloads of money in the long term.

      The wonderful thing about the program, is that it doesn’t care what you build the house out of. It’s mostly concerned with sun angles, window sizes and placement, and insulation levels.

      Give it a try. You’ll be glad you did.

  12. I actually have 2 questions. I am very interested in this typw of construction for several reasons. 1. I used to live in an adobe spanish style house in Florida and loved the look and style. I have moved north to the state of Kentucky and am looking to build once I find the right property. I Like the stucco and adobe look as well as its complimenting ability to mix in with other interior mediums of exsposed beems and rocks and brick works. I wondered how much of an insulation would be needed here since winters can dip a bit low, but it seems that the summers are getting hotter every year, I currently live in a mobile home structure, so I’m used to the coolness of a lesser insulated structures, and like the excuse to light up the small antique woodstove in the winters. The lowest temps we have had here have been in the single digits approx 7 degrees but not below 0 except with the wind chill. summers have been as high as 98 bordering 100 so I am adapted to living in a tin can oven in the summers as well. What would be best to hold the heat of a wood stove in the winter as well as hold in the coolness one usually gets with a adobe type structure in the summer minimizing the contant running of an A/C unit. 2. I was recently dissabled – it seems these homes are being built by DIY folks, could you possibly give some direction of locating a builder at a resonable cost, That would still keep the overall cost low to build one of these type dwellings for someone dissabled?

    • Comfort would be increased with an inch or two of insulation on the exterior, although it sounds like you’ve adapted to colder temperatures and maybe could get by without it. This is the same as in northern New Mexico where adobe houses are similarly insulated.

      I have a blog post about Kentucky coming soon based on the university in Berea: http://erinisbuildingstuff.blogspot.com/

      Search our blog for the keyword Kentucky and you’ll find other projects.

      Consider starting a blog to promote your project. This could attract natural builders to help you out.

      You’re also welcome to post a comment on our free Bulletin Board, where you could let people know of your plans: http://www.naturalbuildingblog.com/bulletin-board/

      • Thank you for you Owen quick reply, I will be sure to post further if we are able to aquire property for our plans. Also I forgot to mention what made me so interested in your earthbag design to begin with was the pretection from tornadoes, after living through Hurricane Andrew in Florida before moving north to Kentucky, and being through many tornadoe alerts this past year here, it is a major need for me being dissabled to be in a dwelling I know I will be safe in since I am unable to move quickly enough to get to a seperate building in a limited warning time frame. I went through the 2 towns in this state that got hist this past summer and was very lucky it missed out town just 45 minutes away, as being I live in a mobile home with no stable dwelling close by to have been able to seak better shelter in the limited warning that was given. I hobble fairly well on a Cane, but haven’t gotten my turbo Scooter yet for making quick retreats in times of Mother earths Dangers,,, LOL

          • Yes, that is what I was looking at – although I was contemplating how the dome would fit in with the style of a adobe/ Italian villa style which is what the rest of the house would look like. After thinking how to make 1 room domed – attached with an acess from within – I came up with the idea of using a domed room off the kitchen for my cool pantry food storage and with the earth grass covering to help with the cool store , I think it will fit quite nicely into my design – will know more once i do up some drawings to get a visual look of how it will turn out. – and on the plus – even though tornadoes hit quick and leave quick – should the other parts of the house not fair well or something block the opening – I wiould at least be where I have food and a shelter i could put a folding sleep cot in as well as a hov-a-round scooter till rescue comes to un baracade the enterance. Thanks Owen for the assistance. Now i Have to Pray The the Lord above blesses me so this makes it from a hopeful plan of desire to being a reality for my future days of my life.

          • That sounds like a good plan, because the cool pantry would serve more than one purpose like you say. One option is to include an emergency escape hatch in case your house is destroyed. Also include a strong steel door to the dome as added protection.

            Note: Most people in Switzerland have fallout shelters. There’s no reason why everyone in disaster prone areas can’t have a shelter for emergencies. The plans for this 8′ diameter earthbag dome are free, and the materials only cost a few hundred dollars. Even if you paid two workers to build it for you, the cost would still be reasonable. (Larger domes would obviously cost more.)

            Consider starting a blog and promoting earthbag hurricane shelters. Your dome could be built during a free or low cost workshop. This could even turn into a sideline business…

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  14. What do you think is the balance of mass vs insulation that would work well in the Santa Fe area? There are a lot of massive old adobe buildings around there with huge walls but no real insulation to speak of that don’t ever really become uncomfortable inside, but a lot of folks seem to prefer more insulation. Or is there some wiggle-room with a high desert climate?

    • The amount of insulated required is directly related to how cold it gets. Santa Fe is at a tipping point where it could go either way (that’s one reason why adobe has been popular in the area). 2″ is common in Colorado. Visit some adobe houses in your area in winter to judge how much insulation is needed. Take into consideration some people get cold easier than others. Also note, many new adobe homes have radiant floor heating systems that maintain ideal indoor temps and may give the false impression of adobe providing the insulation.

    • Nathaniel,
      I have recently moved into the Santa Fe area with the specific intention of constructing an earthen residence/compound. I recognise that your post was made some time ago, so I am curious as to your subsequent experience with it, not only the construction experience itself, but with the jurisdictional and social reactions. I am also interested in reviewing your work and any suggestions you have in this regard. You may contact me directly at kennlutz@yahoo.com.
      Thanks.

  15. Hi Kelley,
    When I went through the engineering stage of submitting plans for building – R value was the major concern. We calculated a value of 1.7. Code calls for R of 15 or 17. It was way too low. The building inspector also queried it and called for an explanation. In the end – he agreed to pass as it is, low R value knowing about the “thermal flywheeling” effect. In reality, if it turns out way out of spec. then I would be obliged to spray with an insulating material. This was the work-about that got the approval. So we intend to:

    Fit shutters to all windows. (Heat and hurricane).
    Put overhangs over all windows. The only external door is covered with a large vault.
    Put large ventilation openings just above floor level as well as a large on at the top of the dome. Heavy through vent in windows too.
    My question for comment is:
    I would have to spray the insulating material on the outside and re-plaster over it. Is this OK. I do not want to sparay foam on the inside.
    If necessary, make a thermally better plaster on the original job. Can you recommend a mix?
    Best regards
    Mike…. floridadomehome.com

    • Spray the foam insulation on the outside, not the inside. That way the thermal mass will work in your favor. Contact companies in your area to determine the best product.

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