Earthbag House FAQs

Here are some questions we’ve received about our earthbag house project, and our answers to them. We’ll add more as the questions come in. Feel free to contact us and ask anything you want!

General Questions About Our Project

Q: What state are you building in?
Answer: We are building the earthbag house in Eastern Kansas—an area that can have hot/humid summers, freezing cold winters, and strong storms, including tornadoes.

Q: Why did you choose earthbags instead of straw bale/cob/adobe/earth berm, etc?
Keith’ Answer: I went with earthbag over other natural building methods for several reasons. Earthbags can use a wider range of clays and rock than adobe. Earthbag walls can also be stacked up higher over the short term rather than having to wait for them to dry as you would adobe. I would have been interested in earth berm, but our land is flat. I find this style very intriguing and perhaps I’ll be involved in this style in the future in some other location.

As for strawbale, I was strongly tempted by this natural method. The insulation is awesome and the walls go up fast Some of the downfalls are that you have to take extra care to not to let the strawbales get wet. The bales can be used to support a roof, but it a rain storm comes during the building process and they’re not covered well, you may have to start over. It’s best to put up a post beam structure, complete the roof, then stack the bales between the beams. Fires usually are not an issue once you cover the walls with a good layer of cob/plaster.

If I would have gone with strawbales, I would have started with the same rubble trench foundation followed by a couple of feet of earthbags (to get away from ground moisture). A post beam structure would have been installed on top of that, followed by the strawbales. In the end I still chose earthbags. The home I’m building is in Tornado Alley here in KS and the bags make a stronger building. Earthbags are great for thermal mass. With the walls over 12″ thick, it will take half a day for the outside heat to reach the inside; thus, the coldest part of the night will be the warmest indoors and vice versa.

The downfall of all this thermal mass is that it has little insulation value. This is why I’m plastering the walls with 2-3″ of papercrete inside and outside. Scoria can be included in the earthbag mix to increase the insulation value of the bags, but there is not a good supply of this volcanic rock anywhere near me.

Q: Will an earthbag house stand up to earthquakes/tornadoes/fire/bullets, etc?
Answer: An earthbag house is very resistant to fire. The mix in the bags cannot burn. The papercrete could smolder if in contact with an ignition source for a period of time. However, the burn would be slow. This would allow plenty of time to locate the fire and extinguish it. When I install the final layers of papercrete, I’ll add sand to the mix which will make the plaster a bit stronger, minimize shrinking, and add additional resistance to fire (this also lowers the insulation value a bit).

Earthbag structures hold up well in earthquakes.  Nepal has received some publicity from their earthbag buildings withstanding their recent devastating earthquake. They also have a good chance of surviving a Tornado. The utility room I included in my building plans begins four feet underground and can double as a tornado shelter.

Q: How big is the house?
Keith’s Answer: The size of the living area measured by the outside of the structure is 1200 square feet. Measured from the interior walls, that space would be around 1000 square feet. The utility room is around 400 square feet measured from the outside. It contains the 3000-gallon cistern, most of the plumbing, the main electrical panel, and space for storage as half of the room is split into two levels (the cistern and lower part of the room are 4′ below ground level). If I were to build an earthbag structure for my wife and myself, it would probably be a third of this size. I’m building a structure this size because it is for my parents for their retirement. They’re accustomed to a much bigger living space. It’s also a central location (in the US) for my family to come together so the extra rooms will be handy for family and friends. Note from Lily: this is a major undertaking and we highly recommend starting out with a much smaller building if you’re thinking of constructing an earthbag house!

Q: Where did you get the design for the house?
Keith’s Answer: I considered Owen Geiger’s plans, but with my background in construction and the knowledge that I had learned about earthbag building (mostly from books), I felt confident in designing my own structure. Most of my knowledge came from the book, Earthbag Building. I Googled floor plans for a three-bedroom house, selected one we all liked, and then I redesigned the walls to conform to the design considerations for earthbag structures.  I added the utility/cistern room to the floorplan.

Q: How much will this house cost?
Keith’s Answer: The total cost of the house will be around $55,000 to $65,000 (the septic system alone is over $10,000 (subcontracted) and buried water/electric lines cost over $8,000 (all done by me with over 1000′ in trenches)). The labor costs will be between $15,000 and $20,000. The roof materials (trusses, plywood, metal roofing) purchased last week cost over $6000. The mix I’m using in the bags is taking about twice as long as what the estimate in the Earthbag Building book listed for a calculation. The book led me to believe that the screenings coming from the rock quarry would be sufficient for bag fill, but this contains virtually no clay, so I have to make a clay slip (make a clay pit, add clay, add water, mush to milkshake consistency, pour though 1/2″ mesh screen into barrels, dump out rocks) and mix it with the screenings in a cement mixer. This takes a lot of extra time, but I’m still very happy with the result.

Q: Where did you get ___? /  Where did you learn ___?
Answer:  Take a look at our Earthbag Building Resources post to find links to materials, books, videos and other things we’ve used to build the house and learn more about how to do it.

The Rainwater Cistern

Q: Why did you do an earthbag cistern instead of tanks?
Keith’s Answer: I primarily went with the earthbag cistern to keep the pricing down and have greater flexibility with the tank design. I had a custom made (9′ diameter 7′ tall with a 4″ overflow drain centered 6″ from the top) cistern liner built and shipped to me before I had even begun building with the bags. The custom liner was about 1/3 the cost of a 3000 gallon tank (<$500 vs. $1500). However, you will have to decide is the savings is worth the extra labor it will take to build an earthbag cistern tank with a liner.

By keeping the cistern built into the earthbag structure, I will not have to worry about freezing in the winter.

By having the round structure incorporated into part of the walls of the utility room and about 4′ below ground gives the rest of the room extra strength and an excellent place to hang out while tornadoes are in the area since my project is in the middle of “Tornado Alley.”

I did not want tanks on the ground surface since transporting rainwater from the gutters to the tank would have been more challenging with higher tanks.

My design is something I’m testing out. I could not find where anyone else has built this type of system anywhere on the Internet before building this one. If any problems come up, we’ll include them in the blog.  Recently we topped the tank off at 3000 gallons and installed the well/cistern pump which is now providing water for our motorhome and for use with the continuing construction.

Q: Why was it necessary to line your hole with earth bags? If the whole cistern was underground would that still be necessary? Or could you line the hole with the membrane?
Keith’s Answer: I wish it could be that easy, but digging a hole with vertical walls and installing a flexible membrane wouldn’t work as the pressure on the walls from the earth around the hole over time would collapse inward. I have researched building ponds and the slopes recommended were about a 5-to-1 ratio (five feet horizontal per foot of depth) to prevent the pond from filling in on itself. Burying a tank designed for burial would be your best bet, but you would still need a way to drain the water below it; otherwise, if the tank was empty and there was a heavy rain storm, your tank could float up out of the hole a bit.

When it comes to building with earthbags, a round structure is the strongest. They prevent the walls from collapsing in on themselves and the barbed wire between rows provides tension to help keep the walls from spreading outward. On the straight walls while building underground, I had to install two rows of bags to add extra strength to prevent the walls from gradually being pushed inward over time.

Q: How will the cistern operate in times when there is very little rainwater?
Answer: Keith designed the cistern’s size based on his estimates of how much rain this part of Kansas receives and the roof size where the rainwater will be collected, plus his estimate of how much water his parents will use. Additionally he took into account how much water could be delivered in one trip by a water truck. If the cistern runs low on water, they can call out the water truck that we used to have our last load delivered. For $75 “The Water Boy” can put in 2,500 gallons, and it should last them a month or so. That’s not too bad considering the monthly water bill in this area is about the same amount.

Q: How much did the cistern liner cost, and where did you get it?
Keith’s Answer: Our custom made 3000 gallon cistern liner cost around $500 including shipping, from polyfabrics.com. A hard plastic tank will cost around $1500 including shipping. If you have extra free labor available, you can save a bit using the custom liner. If you’re paying for some extra labor like I am, it may be better to go with a hard tank and build up the earthbags around it as necessary. I’m still glad I went with the custom liner so I can test out a method that few have used and/or documented well.

Do you have a question we should add to this page? Contact me and let me know, or ask in the comments section below!

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