How to Build an Insulated Earthbag House

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Introduction: How to Build an Insulated Earthbag House

About: Owen Geiger is the former director of Builders Without Borders, a Mother Earth News Green Home Adviser, The Last Straw Journal Correspondent and the director of the Geiger Research Institute of Sustainable B...


For those new to earthbag building, please read my Step-by-Step Earthbag Building Instructable . Also, my new Earthbag Building Guide and Earthbag Building DVD are now available.

Energy performance on most buildings can be improved with insulation, including those made of earth such as adobe and earthbag structures. Although most earthen structures are located in hot, dry climates, there is increasing demand for low-cost, eco-friendly earth building techniques in cold climates. This article explores four innovative methods for insulating earthbag buildings, which extends their building range to cold regions.

Most earthbag buildings use polypropylene grain bags or mesh bags filled with soil. Bags or tubes can be used. We demonstrate bags, because they’re often available recycled for very low cost. The bags or tubes are filled in level courses and then tamped solid. There are typically two strands of barbed wire between courses to bond the bags to each other and add tensile strength. The building process for insulated earthbag houses is nearly the same, although the materials would weigh significantly less and speed construction considerably.

Unlike other earth building methods, earthbag building has the unique advantage of providing either thermal mass or insulation, and therefore can be adapted for cold climates with an insulated fill material. Scoria, pumice, perlite, vermiculite or rice hulls are all suitable insulating materials. These materials are natural, lightweight, easy to work with and non-toxic. Most (all but rice hulls) will not burn or rot and do not attract insects or vermin. In addition, all but rice hulls are not adversely affected by moisture and can be used as part of earth-bermed or earth-sheltered structures. Recycled polystyrene (Styrofoam) is another good possibility. Another possibility is adding foam board or foam insulation on the exterior of earthbag walls, as explained in the 4th option.

The table below compares the approximate R-values of five low cost insulating materials that could be used in earthbags. (The first column in the table is the insulative value per inch; the second column shows the R-value for a typical 15" thick earthbag wall.)
Material -- R-value/inch -- R-value/15"
Rice hulls -- R-3 -- R-45
Perlite -- R-2.7 -- R-40
Vermiculite -- R-2.13 -- R-32 to 36
Extruded polystyrene -- R-3.6 to R-4.7 -- R-54 to R-70
Molded polystyrene (low density) -- R-3.85 – R-58
(Source: Wikipedia Encyclopedia.) http://en.wikipedia.org/wiki/R-value_(insulation)

Tools and supplies:
Shovel, bucket, garden hose, tamper, slider, gravel, soil and/or insulation, earthbags (poly sand bags), barbed wire, wire cutters, level

The following pages discuss four low cost methods of building insulated earthbag houses.

For more information, myYou Tube Channel has dozens of short videos showing every step of earthbag building.  And our Earthbag Building Blog , the number one blog on the subject, covers every aspect of building with bags in detail.


Step 1: Bags or Tubes Filled Entirely With Insulation


The first and simplest method for insulating earthbag buildings uses bags or tubes filled entirely with insulation. The main advantage of this method over the other methods described below is ease of construction. Walls are one bag wide and filled entirely with insulation. Thick earth or lime plaster on the interior provides thermal mass to help stabilize indoor temperatures.

A demonstration home using this method was built in Crestone, Colorado with scoria-filled earthbags. Scoria is also known as volcanic rock or lava rock. It’s widely used in landscaping. Due to its volcanic origin, scoria is filled with tiny air spaces, making it a good insulator. Although the R-value of scoria is debatable, the owner claims these earthbag walls are comparable to straw bale walls of around R-26 to R-30. This estimate includes 5" of papercrete at approximately R-2/inch.

Building a load bearing structure with bags of insulation in this way is still experimental. We’re confident in the working properties of scoria and pumice, but using other types of insulation needs more research. For instance, some types of insulation may compress excessively under loads. Lightweight walls of insulation are not as sturdy as bags or tubes filled with soil and may require some temporary braces. Tubes tend to roll. Round or curved building shapes are more stable than rectangular. Adding vertical bamboo or rebar pins tied together through the wall may be needed. You might also need to use a post and beam system to provide additional support and to meet code. Start out with a small test structure to improve your techniques. It would be great if someone would build some small test structures and document the results. You can join the discussion about Perlite Roundhouses on our blog.

The photo below is of Kelly and Rosana Hart’s Dome Home . Their home has been published in at least 10 books and magazines. Kelly is the owner/author of the number one most popular sustainable building website GreenHomeBuilding.com . His site covers every green building method.

Step 2: Tube Sandbags Filled With Insulation on the Exterior of Earthbag Walls

Another method for insulating earthbag buildings uses tube sandbags, also called traction tube sand bags, typically used to improve automobile traction on snowy/icy roads. (The bags are sold to add weight for vehicle traction.) This method involves stacking tube sandbags filled with insulation on the exterior of earthbag walls, thereby creating a double wythe wall joined together with poly baling twine or with barbed wire.

Tube sandbags provide about 10" of insulation, which is perfect for many climates - not too much, not too little. Again, scoria, pumice, perlite, vermiculite, polystyrene or rice hulls could all be used for insulation. Perlite and recycled polystyrene would be my first choices due to their high R-value and resistance to moisture damage, although the final decision needs to be weighed against other locally available and inexpensive natural materials.

Step 3: Make a Seam Lengthwise Down Earthbags to Create Two Compartments


A third possibility is to add a seam lengthwise down earthbags – either 18” or 24” wide bags – to divide them into two compartments. The outer part could be filled with insulation; the inner part with soil. Like the other systems described here, this would create an insulated wall with thermal mass on the interior. For many situations, especially structures in moderately cold regions, this is an ideal wall system, although the bags would be somewhat awkward to fill.

The placement of the seam could vary, depending on the climate. In a mild climate like New Mexico, about 4"-5" of insulation on the outside would suffice. This would provide about R-10 insulation. In a slightly colder climate the seam could go down the middle (50% insulation / 50% soil). In extremely cold or extremely hot climates I would fill the bags with 100% insulation (or all earth in a hot climate if insulation is not available).

Step 4: Reinforced Earthbag System


A fourth option utilizes the reinforced earthbag system developed by Precision Structural Engineering, Inc. (PSE). Simply add foam board insulation or spray foam insulation on the exterior of earthbag walls. This is probably the most practical approach if you need a building permit. PSE is licensed in 27 states, and they also have reciprocal relationships with engineers around the world that would enable you to get engineer approved plans and building permits almost anywhere. Their fees are quite reasonable. This building system has been covered in detail on our Earthbag Building Blog. Here’s the link to their Reinforced Earthbag Specifications .

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    54 Comments

    Owen -

    I see on one of your follow up comments that you live in a tropical climate. I am currently investigating a dome-shaped earthbag/super adobe to be built in hot & humid Costa Rica.

    I see that you used 18" tamped earth. I am wondering how cool it stays inside your home and what type of roof you're under?

    4 replies

    Read the How to Build an Earthbag Roundhouse Instructable. That roundhouse stays the same temperature inside year-round with no insulation here in Thailand.

    Search our Natural Building Blog for two articles about Passive Solar Cooling. Choose 10-15 strategies and you won't need AC.

    Domes evolved in deserts and so you will have ongoing maintenance trying to prevent roof leaks. All plaster cracks and the water will leak in. Best to build a roofed dome if you want a dome home. See our gallery section at Earthbag Building.com for photos of roofed domes.

    Domes are also a little tricky to build and the fill material needs to be stabilized. The easiest, fastest way to build is earthbag roundhouses.

    Hi Owen, couple of questions!

    1) What temperature does your roundhouse stabilise at in Thailand? How much ventilation does it have built into it (e.g. rough percentage open space in the wall area?) and how wide are your overhangs?

    2) How does it perform in terms of humidity and mold? I have read that for cob construction in particular, cement plaster is dangerous as it prevents water vapour from escaping, causing the walls to liquefy. Lime plaster is recommended for humid environments. What is your take on these statements, based on your experience with humid tropical environments?

    3) Do you know of any cases where earthbag structures have been built to withstand cyclonic conditions?

    I'm an engineering student in tropical Darwin, Australia and I'm looking at doing formal research into the thermal performance of earthbag housing, also the suitability of this type of construction for cyclonic and humid tropical conditions. Any anecdotes you could offer?
    We average around 70-80% humidity, over 30oC for most of the year, with torrential rain for about 4-6 months and cyclones/hurricanes/typhoons.

    Thanks Owen!

    I am considering a group of round houses in Jaco Costa Rica which is pretty hot - probably not unlike where you are in Thailand.

    I have been looking at doing some earth tubes and a solar chimney to pull cool air through tubes that are buried several meters below ground.

    Have you ever tried this? My biggest concern is the issue of potential mold because the climate is humid as well as hot.

    ROOFING Question to go along with cooling:

    I know you use a thatch roof on your round house. Do you ever have trouble with wind? Costa Rica has two very, very windy months with gusts up to 100kph.

    Earth tubes for cooling only work in deserts. Otherwise there are mold problems.

    Use micro concrete roofing tiles instead of thatch. Use anchors that hook under the purlins and strong hurricane ties on the rafters.

    Octagonal and hexagonal shapes are good too.

    I was hoping for a wall the goats couldnt eat through. They always eat through wood. We wanted to go storage container but they are $5000 and up now. If I filled the bags with concrete, and placed barbed wire between, could the goats knock it down while I was in the process? They certainly could help me tamp it down. That would be no problem.

    1 reply

    I had goats many years and are well aware of what they are capable of. They will not be able to knock down a low earthbag wall if it's properly tamped real solid. I'm talking about a small pen or animal shed, not a long straight wall that could tip over. No concrete needed. Round shapes are strongest. They are blast resistant remember. Also hurricane and earthquake resistant.

    Hi Owen

    I am from Seattle, now living in India fir sometime. I would like build a house for my parents and myself , building houses takes 2 to 3 years here which I don't have the time or the money. EARTHBAGHOUSE is new to me:-) , Would any kind of dirt work? (Dry/ damp) Would the cement bags or the rice bags we get in India would work? Also can I mix regular cement with dirt for outer layers to keep the heavy monsoon rain?
    I am planning to go to Tibet next year to help build houses for nuns in a remote area, it's freezing cold in winter so what would be good to build the roof with? Thank you _/\_

    1 reply

    Read my Step-by-Step Earthbag Building Instructable for details such as what type of soil to use. Most any kind of clay/sand subsoil will work.

    Use rice bags or other bags that do not have plastic liners.

    Build wide roof overhangs in rainy climates. Add roof insulation in cold climates.

    How long does it take? It all depends on the size of the house, how many workers you have, how strong they are etc. It's impossible for me to tell you. Build a small tool shed, etc. first and then you will know.

    I live in Alabama so we have basically two seasons coldish and wet (rarely colder than 5℉) and boiling (90-100℉ with 60-90% humidity). The roundhouse should keep pretty cool but the concern is keeping it warm and the walls not melting from the rain. What would be the best insulator? Straw wouldn't be hard to obtain, vermiculite swells with moisture, and I have no idea where to get enough perlite or pumice.

    1 reply

    The easiest way to insulate an earthbag house is to add rigid foam board insulation on the outside, then stucco mesh and cement or lime plaster. Allow wide roof overhangs so the walls never get rained on.

    Earthbags are common in the tropics and no moisture problems so far if you use wide roof overhangs, durable roofing, etc.

    Hi Owen

    I live in northern Minnesota with high humidity and extreme cold and snow. I was reading the article about using recycled Styrofoam to fill the bags. I was wondering about using cement along with chopped up Styrofoam to stabilize the bags, then attaching stucco netting and cover the bags with cement stucco. Will the Styrofoam and cement mixture be stable enough to support a roof? Should I add sand to the mix. Any thoughts or ideas you have will would appreciate. This is a new idea for my area, I would like to build a small building first and then a house. Thank you for your help.

    1 reply

    Mixing foam insulation with cement is not the best option. Heat will still be conducted out through the concrete portion. Adding too much foam will weaken the concrete. So you're better off using other methods such as straw bales and post and beam. Search our Natural Building Blog for an article about Straw Bale Yurts. If I lived in your area I would build something similar to a straw bale yurt using local wood poles and bales. As usual, seek out areas with few or no building codes.

    Hi Owen!

    It seems I am stalking you across the internet.

    Anyway... I commented elsewhere about combining a couple of your plans for an earthbag earthship style design cut at least 6 feet below the frost line. Building is planned for the mid west, so four season climate with freeze.

    I'm here today because I am looking for more info on the EXTERIOR insulation materials between the bags and the berm.

    Most of the plans I see call for rigid form insulation and then a second form of natural insulation before berming.

    1.Can spray foam insulation but used here rather than rigid sheets?
    2 Reading about worries of compression on the actual walls how long is the natural insulating layer good for before it becomes too compressed? (If ever)

    If I am going that deep is that even necessary? I feel like the spray foam insulation is a good call as it both waterproofs and insulates as well as sealing any missed gaps. Offers no structural support obviously.

    Thoughts?

    1 reply

    Yes, you can use spray foam on the exterior. See my Solar Pit House drawings on our Free house plans page for how I recommend insulating the exterior.

    http://www.naturalbuildingblog.com/house-plans/free-house-plans/

    One thing I'm mildly confused about...Can I (in the cold and wet NE US) use perlite to fill my earthbags entirely, or would I use them as an outside insulating wall to an earthbag wall made of...well, earth? Perlite's sort of crunchy and I don't see it being able to support itself being made into a building. It's cost effective and locally produced around here with all the natural vermiculite that I could also use, trusting its less crunchy nature. Which would you suggest that I use in Pennsylvania and how would I use it (directly in the bags or a course concurrently running along side the earth-filled earth bags)?

    2 replies

    Building with perlite, vermiculite and, to a certain degree, rice hulls is still experimental so it's best to build small, simple structures until you develop the necessary skills. See this article called Earthbag Scoria Casita for details on how to stabilize bag walls filled with loose insulation: Watch all the videos carefully.

    http://www.naturalbuildingblog.com/earthbag-scoria-casita/

    I'm willing to try perlite as a small shed project. If it's successful, we'll definitely let you know. I would love to try scoria, but there's just no suppliers up here, whereas there's a perlite plant in Bethlehem, not even an hour away. Vermiculite would be more promising if it didn't expand when wet, and PA gets very wet, except when it doesn't. I'll make plans to make a shed, but it'll have to wait a year. I'm going to be a senior and my studies are about to get more insane. Thank you again for your input.

    To build an insulated Earth-bag House, we can take a suggestion and tips from lesson. Your article is good for this. Thanks.

    http://2jtrakway.com.au/construction/

    Haha given that the house provides insulation, I really don't think houses for sale with these features will do very well in Phuket where it's swelteringly hot almost all year around :)