Cheap earthbag house foundation?

Trying to plan my trench for a big build. Right now it's looking like it's going to cost about $5k just for the gravel. Are there cheaper options? I live in Alabama. We get about 53" of annual rainfall and our humidity hovers between 52 & 80%. Thanks!

What is your definition of "A Big Build", are we talking foot print dimensions? Total interior square footage?

The one thing to remember is that the foundation is no place to cut corners, if it fails, everything else fails.

Have you thought about using concrete rubble?
Are there enough rocks on the property to use them instead of purchased gravel?
How high are the walls going to be?
Are you planning to use wood framing for roof support? Or, are you wanting to use the walls for load bearing?

While your question is a good one, you didn't really give enough information for any thing but a speculative answer at best.

In Alabama (except maybe in highlands, I don't know), you have no significant frost heave depth to worry about, so the rubble trench depth is principally for load distribution to firm subsoil and moisture isolation. That said, what is your subsoil like? As Bryant asks, what rock or rubble resources might you be able to find?

The cheapest foundation is no foundation. We're currently building a house without a rubble trench foundation. We are berming almost all of it. This protects the structure from frost heaving. There will, of course, be a drainage pipe in place around the bottom of the wall to avoid water build up.

What are you building these "no-foundation" walls from? How thick is the base of the wall? What type of soil do you have for the walls to bear on?

Here's a picture of our wall:



The entire wall is built of 14x26 earthbags filled with earth that's a naturally good balance of clay and sand. There is plastic under the bags that will be incorporated into the moisture barrier. The bags are about a foot wide when tamped. The wall is built on compacted subsoil. There will be drainage pipe covered with a silt sock all the way around the base. Since the wall will be bermed up to at least 3 feet or so, there's no way that freezing will reach the base to cause heaving and cracking.

We also put a layer of 1" gravel over the entire footprint and underneath the walls for good drainage.

BTW - I'm in Western NC so our rainfall and relative humidity are similar to where you're at.

Morgan Caraway wrote:The cheapest foundation is no foundation. We're currently building a house without a rubble trench foundation. We are berming almost all of it. This protects the structure from frost heaving. There will, of course, be a drainage pipe in place around the bottom of the wall to avoid water build up.

Not correct, not recommended by many codes and many pros around the world. Protecting the base of a wall from liquid water is usually accomplished by negative grade and drain tiles and is only one part of a robust design.

There are A LOT of fluid dynamics under a foundation, many feet away in all directions, pressures and temperature differentials, many soil properties, water tables, variables, etc….The basic soil property is PI (Plastic Index) that determines how much it shrinks/swells. Without any consideration for frost heaving, the forces from water expansion in an expansive soil can be huge, 1000’s of pounds of force can move high rises. The best designs don’t have high PI adjacent to, surrounding, or within several feet below a foundation. No berm or plastic barrier nor drain pipe is going to change soil properties to prevent it from moving a wall, that is why it is recommended to take several PI test samples at least at two opposing locations around the perimeter of the building, that is min. More at several depths including frost if applicable, better. PI can vary drastically in a building’s envelope and when that happens differential forces act on walls, slabs, footing, etc. If the structure cannot react those forces causes settling, shear wall issues, cracks in cladding/plaster/walls/roofs/etc…..In addition, sites can vary in compression/shear strengths of soils causing similar issues mechanically. …that’s the simplified version of the issues.

To mitigate these issues first off, foundations should be placed on “undisturbed” (not tamped that has low compression and needs to settle over decades) soil per code. This soil type at a minimum has to be able to react the building loads based on its compression strength, preferable shear too. Code has soil compression allowables. If the soil lacks the min. properties it has to be modified, some use a road base to minimize the compression differences, which also makes a good base for rubble trenches. Rubble trenches also provide a capillary break that is needed somewhere, on the foundation or any berm.
3000-10,000 PSI concrete foundation or bedrock provides the highest resistance to building loads and settling ~ 12,000 PSI, or pile drivers to bedrock, although if the mix or sub-soil is not right will still see settling issues.

We dig to frost depths in hopes of finding high PI soils with large water holding capacities that keeps dynamic forces away from foundations. The depth is a function of PI.

“No foundation” with the unknowns denoted above assumes major risk known to mankind all over the world for centuries; one does not have to look far on the internet alone to find. I wish you luck and hope you set it on a strong low PI soil at a minimum.  

You call your wall "no foundation", but from the photo at least some of it was excavated to as much as 6' or more deep, while I presume the other side was barely excavated at all. The deep parts when backfilled will probably have gotten to solid, capable soil which will be protected from frost. The shallow parts may still have uncompressed topsoil, which will settle more than the deep parts and cause cracks, even if the soil is uniform across the site.

I am curious where you got the information that this a safe, durable way to build. Are there any examples that have stood for some years in a temperate humid climate?

How thick is the layer of 1" gravel under the walls, and what kind is it - crushed rock or smooth rounded pebbles?

I have some concern for the walls that will be bermed and not positively curved... straight or negatively curved walls such as in the middle of your photo will have significant tipping forces applied, and stretching forces in the negatively curved portion. What are you using to tie the bags together? Also, in winter you will have moisture moving from the warm side to the cool side, and a vapor barrier on the outside of the wall will ensure that water gets trapped in the outer layer of the wall near ground level. Too much water will weaken the earthbag contents.

When I say "no foundation," I of course mean "no traditional foundation." Basically, what I'm building is an earthbag earthship. The house is being built on compacted sub-soil. In areas where soil has been disturbed, there will be a footer to the compacted sub-soil supporting posts above. The bermed part of the wall be insulated to minimize condensation. The layer of gravel is thin, enough  to minimize capillary action. Will what I'm doing work? Do earthships work? That being said, I'm happy to post updates.

http://geology.com/articles/expansive-soil.shtml
Expansive soils are present throughout the world and are known in every US state. Every year they cause billions of dollars in damage. The American Society of Civil Engineers estimates that 1/4 of all homes in the United States have some damage caused by expansive soils. In a typical year in the United States they cause a greater financial loss to property owners than earthquakes, floods, hurricanes and tornadoes combined.

Even though expansive soils cause enormous amounts of damage most people have never heard of them. This is because their damage is done slowly and can not be attributed to a specific event. The damage done by expansive soils is then attributed to poor construction practices or a misconception that all buildings experience this type of damage as they age.

We've had so much damage especially by our rivers that our BSO now mandates a PI test to get a permit. Or company has made large money on repairs. Due to a lack of knowledge as stated, people that should not be designing homes - feeds our repair company's profits. PI is not enough, it is a battle getting local labs to do the test since they are tired of non-pros not ordering the proper test and builders pointing fingers at them in court when the foundations fail and cause major financial loss. As a result, most only do it for licensed pros.

Morgan, Glenn asked you about the properties of your soils long ago, I am going to guess you have no idea since your have not answered. With that said, no one can properly advise if what you are doing is right or wrong. Earthship is entirely different set of loads and soil requirements compared to what your are doing. The thread is being highjacked at this point with your issues. I chimed in since you were giving bad advice that could cause others severe damage, injury, and financial loss. I suggest starting another thread with diagrams of your design - there may be suggestions to deal with the situ.

The cheapest foundations I heard about are raised on unsettling rock, hard to find, otherwise, if on soils an understanding of soil is needed. IRC 2012 or 2015 code foundation chapter is a good read. In it are rubble, concrete, wood, foundations. Local code and prescriptive paths are always another source of info, otherwise hire a knowledgeable pro since it can be pay now or later.

Terry Ruth wrote:
To mitigate these issues first off, foundations should be placed on “undisturbed” (not tamped that has low compression and needs to settle over decades) soil per code. This soil type at a minimum has to be able to react the building loads based on its compression strength, preferable shear too. Code has soil compression allowables. If the soil lacks the min. properties it has to be modified, some use a road base to minimize the compression differences, which also makes a good base for rubble trenches. Rubble trenches also provide a capillary break that is needed somewhere, on the foundation or any berm.
3000-10,000 PSI concrete foundation or bedrock provides the highest resistance to building loads and settling ~ 12,000 PSI, or pile drivers to bedrock, although if the mix or sub-soil is not right will still see settling issues.

We dig to frost depths in hopes of finding high PI soils with large water holding capacities that keeps dynamic forces away from foundations. The depth is a function of PI.

“No foundation” with the unknowns denoted above assumes major risk known to mankind all over the world for centuries; one does not have to look far on the internet alone to find. I wish you luck and hope you set it on a strong low PI soil at a minimum.  

As Terry says here; IRC is very clear about the foundational footer for any type of foundation to be supported by undisturbed soil. Try this, dig a trench and backfill it, tamp well and watch as it subsides within a year or less.

Rubble trench foundations have no equal in my not so humble opinion. Time tested and inexpensive, while still viable in the modern age. If it was me, I'd be pouring a short stem wall of pumicecrete on the rubble trench in order to get your bags up. but then again, I know little about bag building and would be choosing adobe or cob in order to avoid plastic in my wall system.

Here is an article about expansive clays, where they are found and how to determine if you have themhttp://geology.com/articles/expansive-soil.shtml

All Blessings,
Bill

Morgan Caraway wrote:When I say "no foundation," I of course mean "no traditional foundation." Basically, what I'm building is an earthbag earthship. The house is being built on compacted sub-soil. In areas where soil has been disturbed, there will be a footer to the compacted sub-soil supporting posts above. The bermed part of the wall be insulated to minimize condensation. The layer of gravel is thin, enough  to minimize capillary action. Will what I'm doing work? Do earthships work? That being said, I'm happy to post updates.

Hi Morgan,

Yes, this will work, but probably settle a bit. Earthships have been built all over the world and obviously work if like any design, it is properly implemented. I have been to the community at the Rio Grande to study these designs and was impressed by many of the innovations, but overall I still like traditional homes like the 1000+ year old adobes at Taos pueblo, just over the gorge.

Please do post a project thread and please do not take offense at critiques that are meant to be helpful, not hurtful.

All Blessings,
Bill

Yes Bill, I understand. Not doing a rubble trench foundation is definitely cheaper than doing it, hence my response. Our first earthbag house has a rubble trench foundation. It's worked perfectly for 7 years now, no complaints. It's a good option and cheaper than concrete.