Step 2: Insulated earthbag foundation

Build the insulated earthbag foundation using bags or tubes filled with scoria or pumice. Other fill materials could be used, but they’re still considered experimental. Scoria (lava rock) works perfectly for making insulated earthbag foundations, because it’s insulating, rot proof, fireproof, and doesn’t attract insects or pests. Scoria is also lightweight and easy to work with. It’s almost like handling bags of popcorn. Buy screened ½” scoria for best results. Place the bags or tubes directly on the gravel-filled trench. Check the radius to each bag so the foundation comes out perfectly round.

Use standard earthbag techniques: barbed wire between courses, tamp and level each course (only light tamping required for scoria), angle bag ends toward center and so on.

I am planning to build a strawbale house. Would this type of floor be suitable? Would it support the weight of the bales or would a different material be better for filling the earthbags for support?
<p>This would work. Earthbag foundations are very popular among natural builders.</p>
Hi Owen, <br>Great post as usual, thanks for that! <br> <br>Could wood pallets somehow be integrated into this design, to avoid using (and paying for) concrete? <br>
<p>Sure. We have lots of articles on building with pallets on our Natural Building Blog. One article is on pallet floors, another one is on pallet flooring.</p>
Is it possible to build a yurt with an earthen floor? I really like the idea of the earthen floors instead of concrete. <br> <br>I know using road base as your fill material the bags or floor would tamp very well and become hard almost like concrete. Will the scoria do the same? <br> <br>I guess what I'm trying to figure out is if I can build an insulated foundation for a roundhouse instead of a yurt.
You can do whatever you want:<br>- insulated foundation for a yurt<br>- insulated floor<br>- tamped earth floor<br>- earthbag roundhouse instead of a yurt<br><br>Scoria is totally different than tamped soil or tamped road base. Scoria is light and airy and will remain loose.
Would cob be an acceptable replacement for the concrete and then just build the berm up around the earthbags???? Would it be destroyed in a wetter area? Theoretically all the water would be diverted UNDER the slab, yes? And then into a french drain if one wanted? I have no engineering/architectural skill, and can't really envision the finished product... so speak slowly and in as few syllables as possible.
Sure. See comment above. Add plastic sheeting under the floor to prevent wicking of moisture. You don't have to use cob (which dries very slowly in humid climates). See this list of 11 earthen floor methods: http://naturalbuildingblog.com/ten-earth-floor-methods/
Owen, you're knowledge and willingness to share with your fellow humans is to be commended. I appreciate all the information you've put out there in respect to earth building. Thank you. <br>
I live in Minnesota, my soil is mostly clay. Volcanic glass/rock etc. aren't found here, what can be bought is expensive and comes in small bags. What else can be used for insulation both in the foundation and in the walls? <br> <br>Thanks!
Sometimes it's easiest to add a layer of insulation on the outside of the finished walls. That's what they do with adobe houses in New Mexico, etc. Then plaster over the insulation or add wood siding.
Is this design primarily for colder climates? Is this design necessary for warmer areas...I'm in TX. Also...do.u put rebar in the concrete?
Yes, insulated floors are for cold climates. If your primary concern is keeping cool, then you're in a hot climate and the insulated foundation would actually be counterproductive. See my recent blog post about earth coupled floors that help keep your home cool without air conditioning.<br>http://earthbagbuilding.wordpress.com/2012/04/06/earth-coupled-floors/<br><br>Use gravel for hot climates.<br><br>No need for rebar or remesh in the concrete since there are no heavy loads.<br>
This is interesting, but it is also permanent and requires permits. I am in Maine, USA. So, here is what I am planning to do. I have a slight sloping area, where I want to put a 16 foot(4.87m) Yurt. I will dig a trench, just deep enough to create a level space for cement blocks and to direct any drainage issues away from the yurt. The holes in the blocks will be filled with sand and the interior of the yurt can also have a sand floor. I am also thinking of building and interior wooden floor. The support structure will be landscape pressure treated wood 3&quot;x5&quot;x8', Probably will use untreated 2&quot;x6&quot;'s for the flooring, so I can minimize the number of support beams. The khana or walls will sit on top of the cement blocks, this should minimize the moisture problems with the frequent rains that we get. Since everything will be portable, no permits will be needed. The town has told me that a platform would require a permit. The interior floor would be constructed in sections, so that would also be portable and not require a permit.
Here's an idea for a very simple design that might get around the codes. Stack one course of earthbags in a circle and then fill the interior with sand or an insulating material such as scoria. Spike the bags in place with saplings to prevent slippage. Berm earth against the earthbags to protect from UV rays.<br><br>Optional: Tamp a 2&quot; layer of subsoil on top to create a temporary tamped earth floor.<br><br>I know it's rather crude, but it's also super low cost, quick and easy. No concrete or lumber required, and it should bypass the codes. Please leave a comment if the code officials say this is okay for a temporary platform.
Hello Owen, I would like to thank you for making these wonderful instructables! I am currently an architectural student, and I am very interested in green/sustainable building. Ever since I've stumbled upon your instructables I haven't been able to stop thinking about earthbag construction! I've even shared the idea with my professor and classmates, thanks for sharing this seemingly perfect building solution!
Thank you very much. You should enjoy my new earthbag book. It's getting very good reviews so far by those who work in the earthbag field. I'll post an announcement on our blog in about 3 weeks when it's available.
I hope these instructions are clear. Someone just emailed me and said they thought the center area was a 'hole.' But as you can see in the drawing above, the center is filled with lava rock (scoria). The earthbags insulate the sides, and lava rock in the center insulates the floor. So the foundation and floor are both insulated.
One small suggestion: If you build this foundation higher -- say 4' or so -- then you might want to fill the lower portion in the center with gravel to reduce costs. There's no need for 4' of lava rock. So again, use gravel in the lower part and put lava rock on the top 1'-2'.

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Bio: Owen Geiger is the former director of Builders Without Borders, a Mother Earth News Green Home Adviser, The Last Straw Journal Correspondent and the director ... More »
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