Alternatives to concrete footer/stem wall

Hello,

We are planning a quick tiny house build that will be 12'x12', stick framed, rock wool insulation, with whitewashed earthen plaster over furring strips. The total wall thickness will be about 6". We need to elevate it from ground contact for reasons. We would like to avoid the use of concrete and find a non-toxic alternative, preferably with less embodied energy, and not insanely more labor-intensive to build than pouring concrete into forms. Any ideas?

Apparently most old bricks contain asbestos:

https://www.mesotheliomahope.com/products/bricks/

But maybe new or homemade bricks with a lime mortar?

Adobe bricks couldn't have ground contact either, so the bricks would have to be fired.

Apparently many newer bricks contain some of the same toxic industrial wastes as concrete, such as fly ash. Some it would have to be homemade bricks, and I'd have to find some way to fire them at home.

https://www.masonrymagazine.com/blog/2012/01/23/the-environmental-attributes-of-bricks/

Possibly gravel filled bags with stones along the outside to protect and stabilize the bags until it becomes fully integrated into the supporting ground.

What about a pinned post into stone, sitting in a gravel trench?


Edit: don't forget to turn on closed captioning for commentary on his videos.

I think the issue of asbestos in bricks could be sorted out.
The report mentions fireplaces and tall brick walls.
Further reading pointed out that 'firebricks' were made for a long time, but they are different from house bricks.
They look different also.
From Quora

Yes, there are several manufacturers of fireproof bricks that included asbestos in their products. Harbison-Walker Refractories Co. was founded in 1865 and has produced fireproof bricks and industrial materials for over a century that contained asbestos.
They have been named in several lawsuits since the 1990s after people began developing asbestos-related diseases.
Asbestos-containing products manufactured by Harbison-Walker were sold under the brand names:
Metalkase Firebrick
Micracrete
Chromepak G
H-W Lightweight Castable #10
Other manufacturers of asbestos-containing firebrick include:
Plibrico Co.
A.P. Green Industries
Kaiser Aluminum & Asbestos
North American Refractories Co.
Burnham Holdings

What kind of soil/environment are you building in? Wooden posts can last a very long time if you put 8" of gravel under and pack 4-6" around them. Round hardwood trees are about the best and you would need 4x8-10" diameter. I would dig the hole about 4' down, position and plumb the posts(I stake braces at 90 degrees), then pour and pack the gravel around. Honestly the red bags of Quickrete work really well for the sides instead of gravel; I just pour and pack them dry. After packing, I cut them level(water level) and I would keep the deck at least 18" off the ground. Make sure to shed rainwater away from the structure.

When positioning the posts I put up some batter boards and ram the posts into the bottom gravel a few times to pack everything well.

I often use steel posts, 4 inches diameter, no rotting or rusting if prime painted or galvanised.
Screws can be driven into to them as well. 18V driver.

Old red bricks would not have the extra expense of added asbestos, so unless you have firebrick, you have nothing to worry about.

If locust or another rot-resistant wood is available, that would make excellent piers. Any wood for posts in a dryer climate like Montana, if installed with details to keep it mostly dry, will work for several years or more.

   Hi Jennifer and everyone else,


          Why not use the raw materials that concrete replaced?  Stone. I cannot tell from your post, however if you only need to get it off the ground bit you could look around Missoula and perhaps locate stone that you could use. Reading "The Good Life" by Helen and Scott Nearing, I appreciated how they multitasked when out and about, always gathering stones in their pickup for later use.  They used adjectives like uglies and I think squares to categorize what the stones could be used for. You'd want squares, 2 sides straight or what your think you'd need.
          I suppose if you want to work more, Mark Brunnr's suggestion is the way to go and one I like, although never used. Perhaps, a concern is wind and how to keep you shelter from moving; there are steel anchors for that, more to the point, if that isn't a concern dry laid rock may serve your needs and the needs of all those little creatures who make homes in nooks and crannies. Best of luck on your project!


        Cheers,
        Thomas

If you don't want to use wood posts in the ground, I would advise rubble trench footings, maybe for a 12' x 12' building just four pits with rubble, topped with the largest rocks you can get to the site for stability and to support the floor above grade. Such a small structure should not need footings all the way to the frost line as long as conditions at the corners are the same.

The dermal toxicity of cement (including contact dermatitis from chromium content)

https://pubmed.ncbi.nlm.nih.gov/15068132/

Thank you for all the ideas and suggestions!

Additional information:

This will be built in a humid subtropical climate, so we do want to avoid posts in the ground. In addition, we need a gap of a foot or so between the ground and any wood to make it inhospitable (and inspectable) for termites.

Ideally, the footing would form a solid perimeter, rather than just piers, as we want to build an earthen floor, which needs what amount to retaining walls for the gravel subfloor and earthen floor.

It will need to be a quick build, and neither of us have done traditional rock work before, so we don't really feel comfortable taking on a structural stacked stone stem wall for this build.

The foundation below grade will be gravel on top of compacted earth (essentially a rubble trench foundation).

Chromium leaching from cement

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5923866/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7216133/

From "Use of Non-Portland Cement Lime Mortar for Structural Applications"

"Structural walls, such as CMU bearing walls or retaining walls constructed with NHL mortars,
may need to cure for 24 months before a reasonable, although low, strength can be achieved.
The low strengths can result in thicker, more expensive walls. In addition, the extended curing
times can have a significant effect on construction schedules."

https://www.nps.gov/dscw/upload/TechBulletin0401Rev041107-NonPortlandCementLimeMortar_AF_010418.pdf

Roman concrete is an intriguing alternative, but relies on a specific type of volcanic ash:

https://en.wikipedia.org/wiki/Roman_concrete

I believe the method they used to enclose the earth bags in this build would work if you have the rocks available.

they are planning an earth floor in the earth bag dome.

I am curious about how walls raised a foot off the ground with posts works with an earthen floor on gravel subfloor held in by retaining walls. Will there be a gap between walls and floor?

Slip form rock? It is simple to learn and minimizes the concrete needed.

Since it is such a small house and there is no need for frost protection, why not just use a stacked cinder block foundation only the number of courses high to get away from termites, then add whatever termite shields are needed, I have never had to deal with termites so I can be of no help in that department.

Curious where you got that idea about asbestos? I live in the midst of brick manufacturing  country, on the Hudson River. Dozens of manufacturers. The clay right out of the ground; no asbestos anywhere near here.

Since you want to do an earthen floor there’s no way around stone or concrete footers.
An earthen floor requires You to have a solid form on all four sides to backfill.

Those four sides have to be a material that can withstand the elements. i.e., water from rain, insects, contact with earth, etc.

The only material to create those for sides that can handle contact with earth with out degrading is stone or concrete.

You may want to reconsider the earthen floor idea if stone or concrete work is too difficult for you.

Even though it is the most labor intensive, stone is the least expensive cost wise. Concrete is expensive and so is the form work required for it.

An earthen floor is a dreamy idea, but there’s no way to do it without some stonework.

For a 12x12 cabin, simple piers on grade (either pre-cast or poured) with short 4x4 risers and a wood framed, sheeted (insulated beneath) wood framed floor is a more simple solution. And will require much less labor than stone work.

Joseph Lstiburek of Building Science Institute wrote a great article about building foundations without concrete in the
January 25, 2021 Building Science Insights. I've attached the PDF.

Faruq Hunter from Freedom Nation https://freedomnation.me/builders/area/freedomvillagegeorgia/ (who's built whole villages using onsite, natural materials) told me they use rammed earth foundations on a stone footing.
The climate for they site in Georgia is classified as 'mixed-humid', similar to subtropical for most of the year. They also have to account for termite risk.

Bear in mind Asbestos, when undisturbed, is totally natural and inert (one of its most valuable properties) and poses no risk. It's when it is processed and released it can be dangerous, and nearly all problems are for people working with or living near asbestos processing facilities, or, ironically, in demolition or removal work, facing prolonged exposure to fine asbestos dust.

R Scott wrote:Slip form rock? It is simple to learn and minimizes the concrete needed.

Have you seen the work of Self-assembly lab? amazing;
slip forrm rock jamming
Slipform jam 2

If the building site is near an urban area, I've read about using urbanite (broken up old concrete floors, sidewalks, etc) as stem walls. I understand your concerns about concrete, but the toxins are likely to have already leached out of old concrete, plus it's reusing stuff that would otherwise go to landfill, and is likely to be free apart from the labor, time, and transport costs of getting it to your site.
It's just as hard work as laying stone, however. Here's an example: https://theyearofmud.com/2008/05/02/building-the-urbanite-foundation/

This is a subject of interest here too - we're looking at raising several buildings and refurbishing others that were not built correctly, so foundations have been a topic of much research.

Rubble trench has been around forever and appears to be code-supported in some locales

Earthbag filled with gravel is used for many earthbag or other natural building methods.

Here is a set of links from our reading, perhaps it will be helpful (and lots of other posts here at permies that are helpful can be found with a search in the search bar at the top):

• Rubble Trench Foundation


• Build Naturally...Blog: What is a Rubble Trench Foundation?


• Is a rubble trench foundation legal? - Fine Homebuilding


• Microsoft Word - TRIFOLD-RT.doc


• Rubble-Trench Foundations - Fine Homebuilding


• Rubble Trenches and Lime Mortars to Avoid Cement for Construction Purposes - The Permaculture Research Institute


• Rubble Trench: The Basics | Cordwood Construction ™


• Straw Bale Landscape Walls and Rubble Trench FoundationsStrawBale.com - Your Resource for Hands-On Workshops, How-To Videos & Plans


• Foundations for Earthbag Buildings


• Sustainable Living Center


• Earthbag Foundation


• Gravel Foundations for Earthbag Houses. - THE MUD HOME


• Earthbag Foundations | Natural Building Blog


• Do not use earthbags for stemwall foundation - This Cob House


• Earthbag Construction Footers, Foundation, and Flooring Open Source Tutorial


• Cheap earthbag house foundation? (natural building forum at permies)


• Insulated Earthbag Foundations for Yurts : 7 Steps - Instructables


• Earthbag Building: Foundations – The Free Weekly


• Step-by-Step Earthbag Building : 9 Steps (with Pictures) - Instructables


• Earthbag construction - Wikipedia

Some more info/synthesis of info about the build:

We're not interested in using cinder blocks, urbanite, etc. because of the toxicity issues (use of fly ash, etc).

We're also not interested in using plastic (which probably excludes earthbags).

The earthen floors I have built before just had timbers sills to retain them, rather than stone or concrete, but yes, they need some kind of retaining wall, and in the humid subtropics where this build is going to occur, wood is out.

We are leaning toward concrete (we are fine with making the forms and pouring concrete), but are looking for alternatives due to the toxicity issues and high embodied energy in Portland cement concrete. We would have to buy stone and have no experience laying it, so it's probably out, although I might consider slip form rock with lime mortar, but not sure about the structural integrity without cement mortar. Bricks seem to have at least as much of a toxicity issue as concrete (although a lower embodied energy), but we probably won't go that direction since commercially available and/or salvaged bricks seem likely to present more of a toxicity issue than the concrete.

I'm guessing that the ground-floor-wall interface will look something like: gravel subfloor filling most of the space (probably 12-18") between grade and the top of the stem wall, covered by a few inches of earthen floor to bring it up even with the top of the stem wall (on which rests the bottom plate of the stick framing). It's not very elegant, but it leaves a foot+ of space between any wood and the earth, which is what I want, although it's not really inspectable for termites if the space is full of gravel. However, I can't figure out how to have it be hollow and have an earthen floor, and we really want the thermal conductivity of the earthen floor for cooling purposes. There will probably also be earth tubes for cooling running through the subfloor and up into the living space.

just realized the pdf I provided was incomplete; missing the last 5 pages which has all the stuff about building wood frame on grade (it can be done!). here's a link https://www.buildingscience.com/documents/building-science-insights/bsi-020-wood-foundations-picasso-does-foundations
I've attached the full file here (fingers crossed...)

did someone already mention gabions? https://gabion1.com/ Good for retaining walls and I've seen a cabin built with gabion piers instead of concrete...

What is the potential exposure to hurricanes or other high winds? Do you need to anchor the wooden structure, or will its weight be sufficient?

If the stem wall is backfilled with gravel and earthen floor to the top, there is effectively no separation between earth and wood. It would be good for reducing groundwater wicking, though.

I am imagining it will be anchored with threaded metal rods embedded in the concrete and bolted through the wooden plates. There are some high winds, although we are inland enough not to get direct hurricane winds.

Regarding the separation from the ground, I want four things:

Prevent groundwater wicking
Prevent damage from standing/flowing water
Prevent termite/other wood-eating bug incursion
Prevent rot from contact with soil and its biology

I’m thinking that the gravel-filled space achieves these. There will be a sealed cob floor flush with the top of the footer, which should form an impenetrable ceiling for any termites before they can access the wood from inside the perimeter of the footer, and from outside they will be easily visible before they reach wood (and hopefully will get bored crawling over a foot of concrete and not bother).

Here is a terrible drawing of something like what I’m imagining

check out the pics in the PDF i shared above, esp. the last 3 pages. Note also the drainage on the OUTside of the foundations.

Yes and note rammed earth or CSEB above stone drainage plain forms an impermeable barrier, which can be made by hand with minimal machinery or cement, as Faruq Hunter and his team does https://freedomnation.me/builders/building-supplies/compressed-stabilized-earth-block/.
You can embed anchor bolts and plates into rammed earth as you build it, or between courses of blocks.

Jennifer Richardson wrote:I am imagining it will be anchored with threaded metal rods embedded in the concrete and bolted through the wooden plates. There are some high winds, although we are inland enough not to get direct hurricane winds.

Regarding the separation from the ground, I want four things:

Prevent groundwater wicking
Prevent damage from standing/flowing water
Prevent termite/other wood-eating bug incursion
Prevent rot from contact with soil and its biology

I’m thinking that the gravel-filled space achieves these. There will be a sealed cob floor flush with the top of the footer, which should form an impenetrable ceiling for any termites before they can access the wood from inside the perimeter of the footer, and from outside they will be easily visible before they reach wood (and hopefully will get bored crawling over a foot of concrete and not bother).

stonemason here. 20 yrs exp. i would say scribe wood supports on top of very large stones. the 4 corners should be 1 ton+  size if possible. dig halfway down & water settle the stones for at least 6 months. when they are firmly locked into the earth, begin scribing large posts (12"+) for each individual stone .
 i would just do it all with stone. but i love the work involved. if you need stones, check your local quarry or sand company. nothing good ever came easy eh? best of luck!

I realize I'm 8 months late to this discussion, but I'm surprised to see no mention of earth mortars. It would seem reasonable (to me) that you could combine earth mortars with maybe a slip form like the rock jam video posted earlier to make the stem wall. Most holy buildings (cathedrals, etc.) in Eurasia were built with earth mortars and are still standing today. India had a pretty extensive use of them back in the day, where the mix was a earth, sand, quick lime mixture in some instances. Some of that climate may be similar to yours down in South Texas.

Have y'all made any progress with the build?