Insulated Earthbag Foundations for Yurts

Note: If you’re new to earthbag building, first read the introductory Step-by-Step Earthbag Building and How to Build an Earthbag Roundhouse .

This Instructable includes complete step-by-step instructions on how to make an insulated earthbag foundation. You can use the same process to make insulated foundations for any type of structure – straw bale, earthbag, cordwood, etc.

Yurts or gers are very efficient and practical in harsh, cold climates, as evidenced by centuries of use in Mongolia. Benefits of yurts include affordability, rapid construction, ease of construction, wind resistance, great looks and portability (ability to take your home with you if you ever move). You may even save on taxes since some jurisdictions do not consider yurts permanent homes.

Many people build their yurts on a raised wooden platform to reduce moisture problems. But wood is expensive and building a platform/deck requires a fair amount of tools and carpentry know-how. Wood is vulnerable to fires and prone to rot and insect damage. It also requires regular painting or sealing. And if the wind and snow can blow underneath like most designs, then you’ll lose a lot of heat.

In addition to the many other uses for earthbags (retaining walls, domes, rootcellars, houses, etc.), you can build insulated foundations by filling the bags with insulation such as scoria. The benefits of the insulated earthbag foundation system described here include:
- Very low cost, especially if you can locate recycled grain bags from farmers
- Very simple construction using just a few tools most people already have
- Save energy and enjoy a more comfortable home because the floor and foundation are superinsulated (with no wind blowing under the floor to suck heat away)
- No deep footings/excavation required (see Frost-protected Shallow Foundations design guide mentioned below)
- The finished floor can be raised above grade as high as necessary. Deep snow? Flooding? No problem.
- Building a rocket stove into the foundation for heating.

For those who live in Canada or similar climates, you might want to follow the Earth-Sheltered Solar Canadian blog , who’s planning to build an insulated earthbag foundation that’s suitable for extremely cold climates.

Building in extremely cold climates uses the same process as outlined in this Instructable, but you will need a deeper trench with additional insulated earthbags below grade to create a Frost-protected Shallow Foundation (FPSF) . Combine these two ideas – FPSF and insulated earthbag foundations as shown in this Instructable – and you’ll have everything you need to know for free.

The following instructions assume you have cleared and leveled the site, removed topsoil, and positioned scoria around the building site to minimize work.

3D AutoCAD drawings show each step of construction.

Step 1: Foundation trench

Dig a foundation trench slightly wider than your earthbags. Use string or twine attached to a center stake to define the radius of the foundation. Install a French drain to remove moisture if needed, and then add 6”-12” of gravel or rubble, depending on climate. The depth of the trench will also vary according to climate. Consult the FPSF guide mentioned above for more details. For instance, the drawing shows how earthbags can be started at ground level (‘on-grade’) in mild climates. But for cold climates you have to use additional courses of earthbags that start below grade.

Tip: Throw the soil from the trench to the outside. This saves moving the soil later when you berm earth against the sides of the foundation.

Comments

[seabeepirate]

Is it possible to build a yurt with an earthen floor? I really like the idea of the earthen floors instead of concrete.

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?

I guess what I'm trying to figure out is if I can build an insulated foundation for a roundhouse instead of a yurt.

[Owen Geiger]

You can do whatever you want:
- insulated foundation for a yurt
- insulated floor
- tamped earth floor
- earthbag roundhouse instead of a yurt

Scoria is totally different than tamped soil or tamped road base. Scoria is light and airy and will remain loose.

[jguy2]

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.

[Owen Geiger]

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/

[jguy2]

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.

[nicolepete81]

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?

Thanks!

[Owen Geiger]

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.

[kronological]

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?

[Owen Geiger]

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.
http://earthbagbuilding.wordpress.com/2012/04/06/earth-coupled-floors/

Use gravel for hot climates.

No need for rebar or remesh in the concrete since there are no heavy loads.

[nitepagn]

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"x5"x8', Probably will use untreated 2"x6"'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.

[Owen Geiger]

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.

Optional: Tamp a 2" layer of subsoil on top to create a temporary tamped earth floor.

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.

[TheRealTRA]

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!

[Owen Geiger]

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.

[Owen Geiger]

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.

[Owen Geiger]

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'.