How to Build an Insulated Earthbag House

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, my You 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.

Comments

[candyland22]

I have just stumbled upon earthbag homes about 2 hours ago and have changed my mind from a log home kit to this! I live in upstate Ny and recieved some land from my mother in law in the adirondacks! Would these homes be ideal for the weather conditions? If we had a outdoor wood furnace could we run the heating pipe through the wall without damaging anything? My husband and I are not very construction savvy! Also how do you run electric? Thank you in advance! :)

[Owen Geiger]

You have to weigh all the advantages and disadvantages and decide what's best for you. No one building system is perfect for all situations. For instance, maybe you have an abundance of wood that could be used for cordwood building. Or maybe you have excellent stone for building. Or low cost straw bales from a local farmer...

Everything you need is free on our various websites -- YouTube, EarthbagBuilding.com, Instructables, Earthbag Building Blog. Just google it. Every topic such as how to install electrical is shown in detail.

No problem running pipes through the wall for a wood furnace.

If you do go with earthbags in NY or other cold climate, you'll need to add insulation. Here's one of many free articles that will help you: http://www.instructables.com/id/How-to-Build-an-Insulated-Earthbag-House/

[candyland22]

Now if we decided to expand our earthbag home, how could that happen? Is it possible or would it risk the strength of the structure to cut a doorway out into another room? I also was playing with the idea of a mix of earthbag and cordwood for a more dynamic look.

[Owen Geiger]

It's best to plan ahead because it's difficult cutting out doorways later. One way is to frame a window opening like a door so it's easy to convert to a door later. (Bags sit inside the buck under the window.) Cut the plaster next to the buck, knock out the bags and there's your framed door opening.

Our blog talks about how to use buttresses to join new earthbag walls in the future. This and all topics are covered in detail in 1,100+ blog posts. Use the built-in search engine or buy my Earthbag Building Guide book that summarizes all the most important info. http://www.earthbagbuilding.com/articles/ebbuildingguide.htm

Joining cordwood and earthbags is easy if you make the cordwood the same length as earthbags (about 18").

[candyland22]

Thank you for all your help so far! Im purchasing your book as soon as the land is in my name! I was GIVEN 5 beautiful acres (thank you mother in law) so this really is going to be quite the low cost home!

[CarolAnn525]

Hello Owen,
My husband and I just got your book and are very excited about building.

We are planning to build in northern Minnesota and are wondering if anyone knows of an earth bag home in this state. I know of a straw bale home but not an earth bag. Would the building codes for earth bag be the same as straw bale, or comparable?
Also we plan on a 50/50 mix of volcanic rock to native earth. Do you think that would be a good insulation? Should we insulate the exterior as well? We also want to build a basement either under half or the whole structure, is that a good idea? Can it be done?


Thank you for your help with our questions. G-d bless you for your knowledge and consideration, CarolAnn

[Owen Geiger]

I don't know of any earthbag houses in Minnesota, but then again most people don't publicize their projects. Earthbag and strawbale both fall under the Alternative Materials provision of the code. You'll need additional exterior insulation in Minnesota. Earthbag basements are still experimental. Using ICFs would likely prove more expedient and realistic for most.

[CarolAnn525]

Thak you Owen,
I will let my husband know and continue on with the resurch. I will keep you psted as we move forward. Go-d bless, CarolAnn

[winsulation]

Benefits of polyurethane spray foam insulation:
http://weatherfoam.com/

[mstricker]

I have been researching earthbag houses in hopes of building my parents a new house on their land in Northwest Missouri. They need something well insulated as it can get quite cold in the winter and is very hot and humid in the summer. Our funds are extremely limited so I was thinking the rice hulls make the most sense for us economically but was wondering how much they would be affected by moisture. Not only is it quite humid but they are in the Missouri River flood plain and also get some tremendous thunderstorms. I was planning on trying to build the foundation up with concrete rubble and gravel filled sandbags for the first few feet to help minimize the flooding damage. I would love some advice and encouragement on this. Will rice hulls work in this wet climate and any suggestions on building up the foundation? All and any advice appreciated and welcomed!

[Owen Geiger]

We know of at least one earthbag house in Thailand made with bags of rice hulls. I was just in contact with him and his house survived the first rainy season. They get lots of rain and so what you're proposing is possible. I wouldn't risk it on a large, expensive home, but it should be fine on something small and simple. You have to be super careful the rice hulls don't get wet during construction, from roof leaks, leaks around windows, etc. It's taking a risk for sure. Maybe build a post and beam frame, finish the roof with wide roof overhangs and install the rice hulls later.

I would use broken rubble in a rubble trench and then fill lower bags with crushed gravel up to about window sill height.

[chrisandamanda]

Just a question but could you not use a Styrofoam sheet and attach it to the walls at all? Kind of like they do to a house that they are re-plastering?

[Owen Geiger]

Sure, that's the easiest way, but styrofoam is not good for the environment so I'm suggesting alternatives.

[chrisandamanda]

I mean polystyrene I know that they can come in sheets. I love this idea. I live in Canada would this style of building work in a cold wet climate?

[Owen Geiger]

Polystyrene is the same as Styrofoam. I show recycled polystyrene peanuts in this section view: http://earthbagbuilding.wordpress.com/2011/09/15/solar-pit-house-building-details/

So yes, this can work in Canada with a moisture barrier to protect it.

[mike poind]

so what is the R factor of a earthbag wall/home useing soil & clay as bag fill

[Owen Geiger]

A quick google check says .25 per inch. Typical earthbag walls once plastered are 18", so 18x.25=4.5 R-value. This is suitable for mild climates (where adobe houses are typically built). You can use insulated fill material in colder climates or add insulation on the outside.

[armynavy17]

Good instructable. I'm curious though, on your website you have plans for multistory homes, yet you don't explain how one would do the floor of one of these. That's my question, how would one build the floor of the second level?

[calgarc]

you can do a loft type setup by having a portion of the second floor usable and use pillars to hold it up.

[Owen Geiger]

Yes, lofts are a great way to add extra space inexpensively. You may not need pillars, depending on the span. I particularly like sleeping lofts because they're warm and cozy at night.

[Owen Geiger]

There are numerous possibilities for building second stories. You could use the Precision Structural Engineering, Inc. method. You could use post and beam or confined earthbag. You could build a lightweight second story. Use the search engine on our blog. Every topic is covered.
http://earthbagbuilding.wordpress.com/