Would an Earthbag foundation work for a balecob house?

I’m hoping to build a bale cob home on my property once I get the land filled in the next two years. I was originally thinking of doing a concrete foundation, but someone mentioned that I should do an earthbag foundation. I love the idea, but most of the earthbag foundations I’ve seen are a smaller dome type and are fully earthbag houses. I live in a colder climate so I’m planning on going with bale cob for some extra warmth in the winters. My current design has my house being 25 feet by 20 feet and a second story of 10 feet by 20 feet. I want my house to outlive me so I want to make sure I pick the best foundation for it. Does it sound like an earthbag foundation would work or should I switch my gears back to concrete?

Hi there, I am currently building an earth bag house and several sections will be bale on earth bag, I have read and seen photos of it in various places. With straw bale I am doing 2 courses of bags minimum  above grade before I set the bales, in most places my bags are 4-6 courses before I set the bales. I am building into a hillside so I want to be sure that my bales won’t get wet when heavy rain comes. I’ll try and find an article on bag foundations and post a link to it.

Found it ! https://earthbagbuilding.com/faqs/otherfound.htm

Erastus Cooley, thanks for the info! May I ask how big the house is your building? While I have seen many people posing that they are doing an earthbag foundation, the size of the house is usually only half of what I want to build, I'm worried about that.  

So I am building several interconnected domes, and a 2 story round building. A 14’, two 16’ domes. A15’dome. 12’ round house plus the 7’ root cellar.the round house and 2 domes will share a continuous footer. Plan subject to change!

How neat!!

Thanks, I hope my information is helpful. If you’re wondering where the Strawbale comes in on my build, it’s going to be my bedroom and the back utility room. What size are you planning?

I'm still planning, but it's looking like 25 feet by 20 feet and a second story of 10 feet by 20 feet.

Very nice, I wish you all the best!

Hi there Assilem,

I'm focussing here on something in your description "I’m hoping to build a bale cob home on my property once I get the land filled in the next two years. I was originally thinking of doing a concrete foundation, but someone mentioned that I should do an earthbag foundation.   "Once I get the land filled" caught my attention.  Can you explain that a bit more?   On the face of it, sounds like you're planning to build on filled land?

No matter what kind of  building or foundation you decide on, you should try to place it on the most solid ground possible.  If you don't your foundation can fail, and the walls can settle, crack, and result in all kinds of other problems that reduce the building's lifespan.

Where I live and work in the Western United States that's often referred to as "native soil" and specifically not filled land unless the fill was structural, e.g. compacted gravel.  The footing for straw bale structures is wide for several reasons.  Plastered bale walls are wider and  4 x to 5 x heavier than conventional construction wall assemblies, and the wider footing helps transfer that load evenly to the ground.  And cob is much heavier than straw bale!

In some soils and climates foundations must "float" over softer soils, or be able to withstand the freeze-thaw cycle of permafrost.  These may require even wider footings, or drainage under and around the footing, or insulation, or all three.

Height above grade is also covered in the IRC's Appendix S: Strawbale Construction which several US states have adopted.  The 8" above grade requirement is to protect the wall surface from splash back, which can also be achieved with really wide roof overhangs.

I'm not as familiar with eartbbag foundations as with concrete, but if you live in an area with earthquakes, you'll want to learn more about how they perform--you don't want your walls "dancing" off the foundation during a seismic event!

Jim Reiland
Many Hands Builders

Hi Jim,
Thanks so much for the information. It being on filled ground was one of my biggest worries. The land isn't filled yet, so I'm researching doing a pier foundation or a ground screw pile before we fill. That way it will be into the solid ground then it can be filled after.

OK!  Just keep in might that overall wall weight.  A straw bale wall with plaster on both sides, and some framing, can weigh 45 lbs. to 55 lbs. per square foot.  If your wall is 8' tall, that's 8 x 45 lbs. or 55 lbs. per lineal foot.  Two story buildings have heavier walls, and the footing/foundation must support them.  And cob weighs much more than straw bale--perhaps 70 lbs. per square foot depending on density and wall width, so you're talking about a lot more weight.

Most of the United States is covered by building codes and a permit process, and we often require engineering for a custom building.  If you're building in a place that has building codes or requires permits, you'll probably need to have a structural engineer take a look at your plans and design something appropriate to the wall weight and soils.  Although this can be costly, that cost is a tiny fraction of the expense of replacing or repairing a house that is failing and is dangerous to live in.  

Since I get to repair a fair amount of poorly designed and built straw bale structures, I can tell you it's much less costly to just do it right the first time!

Jim Reiland
Many Hands Builders