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The Freaky Cheap part of WOFATI not so cheap?

 
Justus Walker
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Location: Siberia
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Hi All! I just ran the numbers on building our next home. It looks like a 1500 sqr food wofati will run me about $25k.

All my own labor (except excavation). I'm planning on using new windows and new doors, doing a scratch cement floor, and using a RMH as a heat source for the winter. Interior walls (dividing rooms) will be aerated foam concrete with an adobe finish (hard to believe but after the bags, chicken wire, barbed wire and thicker layer of plaster building with earth bags seems MORE expensive than using aerated crete, strange). I will have a PAHS style umbrella with insulation as well as breathe tubes. Standard electric wiring, Whate, black and grey water systems.

This comes out to less than $17 per sqr ft and I was wondering if that IS freaky cheap or should I be working to make it MORE freaky cheap.

I prefer to buy new energy star windows and good doors because what I gain by scrounging windows I loose (I think) in energy loss. In fact I'm not calculating on scrounging anything. Scrounging is a whole different deal when your not in the good ole' USA!

What do the great guru's of alternative construction say??
 
R Scott
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That sounds pretty cheap by US standards. What does a conventional build cost in your area? What about similar energy efficiency conventional?

To get to FREAKY cheap, I think you need to harvest your own wood from onsite for everything. There is no way to stay cheap if you have to buy anything.
 
Dave Hartman
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I believe you would get better solar gain with non energy star windows.
You may want to reuse some windows to keep them out of the landfill and save some money as well. Just my opinion though.
 
William Bronson
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Why the foamed concrete interior walls?
Surely insulation isn't desired, is it cheaper than brick, block, stud walls etc?
 
Michael Cox
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Agreed about the foamed concrete walls. The ideal arrangement is to have you insulation on the OUTSIDE of the thermal mass. Basically you want it immediately beneath the waterproof membrane.

The whole point of WOFATI as I understand it is that the living space is closely coupled to the thermal mass of the surrounding soil, so it stays cool in summer and that heat is released back in winter. Insulation between the living space and the earth hinders both of those processes.
 
Justus Walker
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Just judging from past experience, in our area when you need heat the most (Nov-Feb) the heat coming through those windows is very little compared to the heat going out. -40 outside tends to make a huge pull on the heat inside! That's as far as the windows go.

Aerated concrete blocks aren't all that good insulators (better than wood, worse than fiberglass) And I'd use a six inch block (standard exterior wall aerated concrete foam blocks are 12"). The main purpose for this is sound insulation. In my economic context, stud, fiberglass, sheet rook, mud, tape, plaster, paint walls are not cheap and they give more thermal insulation and less sound insulation! Brick is more expensive by a long shot. My design is a urt style house converted to wofati. The floor plan is like this...



I'll have a rocket mass heater in the living room (central octagon) area to keep the chill off and the outer ring should be sufficiently connected to the earth for adequate transfer of heat.

A normal house would cost a minimum of about $30-$40 to construct per sqr ft. So. But then I don't have to deal with all the permitting stuff (code, septic, building permits, etc)...yet.




 
Justus Walker
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Yah, unfortunately harvesting trees would mean actually having a piece of property in the woods which seems like that is something the russian government just doesn't like. "Citizen, you must live on a half acre lot (MAX) inside town!"

I just ran the numbers, harvesting my own timber would bring the expense down by about $3 per sqr ft.

This has value for you guys since, with rare exceptions, building materials here are as expensive if not more expensive than state side. Plus you can scrounge!

I have nothing against scrounging, by the way. Just that the Russian society at large is not to the level of opulence that the US society is that people are often throwing out tons of good stuff. I've done some scrounging in the US (when I've been home on furlough) and it seems to me that in that land of fattened calves and suckling pigs, where the junk yards flow milk and honey, one could build for...maybe not nothing but VERY little!

Just an outsiders observation.

The problem in the US is permits, codes, zones, regs, etc!
 
Abe Connally
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Deconstruction! Get paid to scrounge for free building materials. Dale's the resident expert on this, but basically, find people who own building that want them torn down, and salvage what you can, sell the rest. You'll learn a lot about construction in the process.

It's hard for me to imagine that concrete blocks are cheaper than earthbags, but I guess if you have to buy a lot of labor or something, they might be. If you are burying the earthbags, you don't need external stuccos, and internal could be gypsum based, which is sticky (use cheaper mesh) and a lot cheaper than concrete-plasters. You can do adobe finishes and earth-based floors, instead of concrete, to reduce that cost if needed. Why are you buying earthbags? Search out a local source, like an animal farm (feed bags) or something similar.

The key to ultra low cost construction is using resources you already own or can be collected for low cost. Scrounging is part of the deal, but I think if you look at the breakdown of cost, doors and windows make up a very small portion of the cost of the house, and the vast majority of cost will be in the roof and foundation. So, that's where your cost-cutting focus should be.

What local resources are available? Is there wood, sawdust, adobe, clay, rock, etc?
 
Justus Walker
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Thanks so much for all the replies.

Earth bags vs. blocks

1). Have to buy bags here. Bags cost $0.30 new and $0.24 used. No free bags that I've found. In fact when I buy feed or flour I have to bring an empty bag to exchange for the full bag!

2). Chicken wire and barbed wire, not cheap.

3). I'm basing my assumptions on a cement based plaster. The blocks don't need chicken wire and they need a very nominal coating. Now if I could use a more natural plaster (stucco or cob or adobe) then I might be able to do earth bags cheaper. I'd have to recalculate. I've never done anything with adobe or stucco or cob and would like to learn. Gypsum? Maybe. Cheap as dirt hear.

4). My floor is a HUGE cost factor. Could I do a floor in cob, adobe or stucco? How clean is that? How cleanable? Waterproof? If I spill a pitcher of water do I get a mud puddle in the middle of the kitchen?

5). Heating system. I said I planned on putting in. A rocket stove but I calculated the cost ov that as the same as putting in a hydronic (in floor) heating with a cast iron wood fired boiler. I've done a number of these systems and know that I can put one in for about $5-7 per sqr ft. That's a huge chunk of change. How much will a RMH cost to install? Ballpark?

I am doing all the labor myself and a couple of volunteers so labor makes up 0% of my costs.

I'd love to scrounge but here scrounging is just not like in the US. You go and ask someone to take down an old building for them and they'll start negotiating with you on how much you'll pay them for the privilidge!

Down in the big cities maybe, but not in the rurals!

Any one know some good books on Adobe, stucco, cob? Sites for newbs?

Thanks all!

I'd like to get my estimated costs down to about $10 per sqr ft. That would be...life changing.
 
Abe Connally
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Justus Walker wrote:1). Have to buy bags here. Bags cost $0.30 new and $0.24 used. No free bags that I've found. In fact when I buy feed or flour I have to bring an empty bag to exchange for the full bag!

what about other types of bags, like onions bags? where do all the used grain and feed bags go?

Justus Walker wrote:2). Chicken wire and barbed wire, not cheap.

you don't have to use those materials, find a local, cheaper alternative. You can use rebar to pin the bags together instead of barbed wire.

Justus Walker wrote:3). I'm basing my assumptions on a cement based plaster. The blocks don't need chicken wire and they need a very nominal coating. Now if I could use a more natural plaster (stucco or cob or adobe) then I might be able to do earth bags cheaper. I'd have to recalculate. I've never done anything with adobe or stucco or cob and would like to learn. Gypsum? Maybe. Cheap as dirt hear.

you can use adobe/cob to smooth out the wall and then use a think layer of cement plaster to top it off, but if you are burying it, you don't need a plaster. The plaster is to protect the bags from UV damage. It could be anything that is cheap and available and lasts in your climate.

Justus Walker wrote:4). My floor is a HUGE cost factor. Could I do a floor in cob, adobe or stucco? How clean is that? How cleanable? Waterproof? If I spill a pitcher of water do I get a mud puddle in the middle of the kitchen?

It depends on how you make it. I have an earthen floor, and my wife mops it every week. Here's instruction on how to make Cheap and Easy Brick Floors If you could find a source of local used bricks, that floor could be almost free.

You can also do a floor like mike oehler. He compacts the earth subfloor, then puts down a plastic vapor barrier, then carpet on top of that.

Justus Walker wrote:5). Heating system. I said I planned on putting in. A rocket stove but I calculated the cost ov that as the same as putting in a hydronic (in floor) heating with a cast iron wood fired boiler. I've done a number of these systems and know that I can put one in for about $5-7 per sqr ft. That's a huge chunk of change. How much will a RMH cost to install? Ballpark?

It depends on what you can find as far as salvaged parts, etc, but I made our RMH for $200.

Justus Walker wrote:I am doing all the labor myself and a couple of volunteers so labor makes up 0% of my costs.
Have you considered making bricks yourself from local soil?

Justus Walker wrote:I'd love to scrounge but here scrounging is just not like in the US. You go and ask someone to take down an old building for them and they'll start negotiating with you on how much you'll pay them for the privilidge!

Down in the big cities maybe, but not in the rurals!
All you need is one building, maybe from an older person or someone that lives int he city? It is worth a look.
If you can't find it locally, go to the cities to get your materials from a deconstruction, there. If you get paid to scrounge, it would be worth the trip to get your house for free.

Justus Walker wrote:I'd like to get my estimated costs down to about $10 per sqr ft. That would be...life changing.
The key to that price range or lower is using resources you have. Low cost isn't easy, you have to work for it, find deals, and make the most of local resources.
 
Andrew Parker
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Your yurt floor plan reminds me of earth lodges. Perhaps you could borrow some ideas from them? I have considered a design using a cribbed roof (like a Navajo hogan) over the central space. Only downside is that it requires a lot of wood. Can you get suitable poles nearby for not too much money?

What are you planning to use to seal and insulate your PAHS umbrella?

Siberia covers a lot of territory. Can you give us a better idea of where you are and what local conditions you are dealing with? Do you have permafrost?
 
Justus Walker
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Thanks so much for the input! Bricks and bags are sold and resold until there is nothing left of them! Old rebar might be cheaper.

I'll look into the adobe and stucco plasters as alternatives to cement. I really want a hard floor. Carpet I do not like. Throw rugs on a hard floor is what we're working for!

Wood hear can be had not too expensively. And it is some of the only material that can be scavenged. Poles no prob.

I'm at 57.61 N 96.7 E

No permafrost yet.

For the PAHS umbrella I'll be using a polyurethane sheet insulation and the heaviest gauge reinforced plastic sheeting that I can find.

I'll look at that earthen floor link!

I have thought about making my own bricks but it seems like a LOT of work. Not that I'm against work, just want it to be rational!

I'll look into earth lodges!

Thanks so much everyone!
 
Jeff Higdon
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I tried uploading pics from my phone I took a couple of weeks ago but it didn't go.
I took pics of the Mandan Indian tribe's earth lodges in New Town, North Dakota.
They are built in an octagon, just like yours. The outside ring has post about 5' tall spaced maybe 8' apart. There are logs connecting the top of the post together.

In the center are four post in a square, with logs connecting them together in a square on top of them.

Around the outside, short poles are leaned against the perimeter. Then, longer poles are laid from the top of the outside plate (the octagon), to the top of the inside plate (on top of the poles arranged in a square).

This forms a circle at the very top, which they left open as a smoke hole.

Inside the square in the center was a huge fire pit.

The poles were covered with thin branches, straw, then about 6"-12" of dirt.

This is what they lived in with winters getting down to -60 or even colder.
 
Peter Ellis
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Abe Connally wrote:Deconstruction! Get paid to scrounge for free building materials. Dale's the resident expert on this, but basically, find people who own building that want them torn down, and salvage what you can, sell the rest. You'll learn a lot about construction in the process.

It's hard for me to imagine that concrete blocks are cheaper than earthbags, but I guess if you have to buy a lot of labor or something, they might be. If you are burying the earthbags, you don't need external stuccos, and internal could be gypsum based, which is sticky (use cheaper mesh) and a lot cheaper than concrete-plasters. You can do adobe finishes and earth-based floors, instead of concrete, to reduce that cost if needed. Why are you buying earthbags? Search out a local source, like an animal farm (feed bags) or something similar.

The key to ultra low cost construction is using resources you already own or can be collected for low cost. Scrounging is part of the deal, but I think if you look at the breakdown of cost, doors and windows make up a very small portion of the cost of the house, and the vast majority of cost will be in the roof and foundation. So, that's where your cost-cutting focus should be.

What local resources are available? Is there wood, sawdust, adobe, clay, rock, etc?


As I understand it from both training as a real estate appraiser and a fair bit of reading about various alternative construction methods, the roof and frame are actually the least expensive elements of any sort of residential construction. Where expenses come in and rapidly rise is in the amenities and the finishing.

Rammed earth, for example, can be done for very, very little money in construction of the shell of the structure. Running wiring for electrical, plumbing, floor finishes, wall finishes, windows, doors, HVAC - those add up very fast and make up the bulk of the cost in many houses. As you go from really inexpensive toward really expensive, they make up greater and greater portions of the expense.

It seems to me that our OP is putting lots of "extras" into his structure, in terms of electrical wiring, interior walls, etc.

And the gur shape is not optimized for passive solar. It's good against wind, when sitting on the vast open steppes. Where you are planning on putting the house substantially into the ground, the benefit of wind resistance is not important anymore, and the less than optimal format for passive solar becomes very important.

But just in terms of why this does not seem like the "Freaky Cheap" that wofati offers - I think it is because there is lots being put into this design that is not contemplated in the "typical" wofati.
 
Andrew Parker
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I agree, in part, with what Peter has written. The cost of the structure itself is often less than a third the finished cost of a conventionally built home. After that, it is death by a thousand details.

The cost of the roof of a WOFATI design is going to be more expensive than a conventional roof, in order to hold the additional dead load as well as the insulation and waterproofing.

I think the circular shape will work fine for the OP, Justus Walker, given the bitter cold he has to deal with in Siberia. Skylights can efficiently flood the interior with natural light, when it is available, and keep heat losses to a minimum. A greenhouse or solarium can be built on the south side and small courtyards (large lights wells or window wells), covered or not, can be built into the shaded slopes to give additional light and emergency egress to perimeter rooms. Passive solar can also be used in the form of trombe walls and active solar is always an option to heat the mass under the umbrella throughout the year.

As far as I know, there is no finished WOFATI yet, so there cannot be a typical one. While the Oehler design uses hillsides, there are a lot of people who don't have a hill on their property. There is no reason why an Oehler home, or a WOFATI, cannot be adapted to flat land. The first PAHS home was built on flat land. I will mention the earth lodge once again. Also, look at Romanian burdei.

On reviewing the proposed floorplan, I would suggest that the bathroom and kitchen share a wall, to minimize plumbing, also, the bedrooms should be clustered in order to share a mass stove (rocket or otherwise) Of course, if hydronics is used, it wouldn't matter.

If you want freaky cheap -- keep it simple.
 
Dustin Hollis
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What about ferrocrete but with wofati design, like this?

http://ecuadorcommons.com/page3/page3.html

I have seen people do this and then spray foam on it then cover it with dirt.
Then plaster it on the inside. It's beautiful when done. Cody Lundin did his house this way.
 
Andrew Parker
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Dustin, very nice. Ecuador is a beautiful country and I do like the area around Cuenca. I am not sure why they need PAHS there, since the temperature is pretty consistent throughout the year, though the day to night temperatures in the Sierra can vary quite a bit. Those skylights will work especially well with the equatorial sun. Ferrocement domes were fairly common in Ecuador, back in the '60's and '70's.

You would want to forgo any foam insulation on the dome, if you will by using it as a PAHS. Monolithic's EcoShell inflatable/reusable form would probably also work but you would need to increase the amount of reinforcement and the thickness and makeup of the concrete, based on an engineer's calculations.

It looks like they fabricated some curved trusses to make their compound curve dome. I don't know if they need trusses for the finished structure or if it simply facilitated the construction of the reinforcement. Monolithic puts reinforced beams in their larger designs. I will be interested to see if they can get the same elegant look using conduit geodesic domes as forms.

Perhaps Paul might invite them to present their designs?

Of course, you realize that you may well instigate an anti-cement rant, but I trust the members here are accepting enough to let it slide.
 
Dustin Hollis
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It seems an interesting solution. I just discovered it from Owen Geiger's Earthbag Blog.. I also saw a video about Cody Lundin's house which is built in the same manner (http://www.codylundin.com/wordpress/cody-lundins-homestead/). One thing about those designs is that the amount of concrete is minimized.
I really like the Oehler designs too. I think the ideas are in a similar vein, and might be attractive to folks without cheap accessible large timber (say in a desert). You could go with earthbags, but they are pretty labor intensive, like tires in an earthship.
 
Thomas Vogel
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Kudos to Mike Oehler for his life work. However, I'm intrigued to see only occasional minor passing references to John Hait's work at Rocky Mt. Institute. A Massoula man no less, he gets very little play. That said,

I've seen no discussions on Hait's perspective, insulating "the umbrella" in a 20' perimeter around the structure and NOT insulating the subterranean walls. The umbrella appears to have taken centet stage but 4" of polysytrene beneath-- I do not see. Also missing are the "paired earth tubes" which according to Hait convect forcefully enough to blow out a candle.
Hait's premise is to deposit heat in the bank without allowing thieves (water and frost) to rob the account before it can be utilized by the account holder.
I've tried to understand how Mike Oehler can stay warm living against (dry) earth when cold penetrates it as deep as four feet, as it does here in the Adirondacks. I mean...who walks their dog in frozen weather with just a rain coat?
Thanks for considering,
Tom




 
Andrew Parker
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Thomas, Paul's WOFATI is an homage to both Oehler and Hait. The polystyrene is abandoned, but not the insulation layer. Polystyrene is not the only insulation solution. The air tubes may work, but they bring complications that many builders would rather not deal with. There has been considerable discussion of PAHS at this forum and there will likely be more.
 
Thomas Vogel
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Thank you Andrew. I found others with the same questions and concerns in a PAHS forum elsewhere. I'll have John Hait's book from inter library loan in a couple days.

Homage to Innovators is fine as long as their concepts actually work (moldy airtubes? Yuk maybe.) and we copy them to the letter. Hait claims an R-39 insulation (it doesn't have to be polysytrene, of course) in the Mother Earth News article. Paul claims an R-11 for all materials in the wofati. Thus, my concern.
 
Andrew Parker
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The important phrase is, "as long as their concepts actually work." There seems to be a lot that remains to be proven, but that shouldn't stop folks from trying, as long as they understand and accept the risks.
 
Weston Ginther
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Justus Walker wrote:4). My floor is a HUGE cost factor. Could I do a floor in cob, adobe or stucco? How clean is that? How cleanable? Waterproof? If I spill a pitcher of water do I get a mud puddle in the middle of the kitchen?


Now most of my knowledge about this subject is theoretical so if someone out there with more experience sees something wrong, please point it out. Since this question hadn't been addressed directly, I figured I'd give it a shot.

From my understanding an earthen floor has the potential to be easily cleanable while staying relatively clean (free from dirt, dust, etc.) afterwards. If an earthen floor is done correctly, you should not have an instant mud puddle if you spill a pitcher of water. That water, does however, need to be mopped up fairly quickly. When working with any type of earthen material (floors, walls, etc.) I believe the idea is to allow the air and moisture to pass freely through the material. I think you would want an earthen floor to be more water resistant than waterproof.


Justus Walker wrote: Any one know some good books on Adobe, stucco, cob? Sites for newbs?


"The Hand-Sculpted House" by Ianto Evans is a great resource on this subject. I'm sure some quick searching would yield dozens of other great books, as well.


I think if you can find a way to replace the concrete foundation with something else, you would be much happier with the cost of your home. When reading your initial post the main thing that stood out to me was the 1500 sq ft and the idea of using a concrete foundation. Concrete is pretty expensive and doesn't look all that great. Although a WOFATI is designed in such a way that it doesn't need to utilize passive solar, I don't think it would necessarily hurt the design if it was added into the equation. If that is a consideration, it is important to have the mass of the floor be fairly thick to allow for good solar gain. This makes concrete an even more expensive option. An earthen floor can often be constructed with material from the building site which would mean you could have a really thick floor for nearly nothing (expect your time, of course). If you are up for the challenge, I think eliminating the concrete and replacing it with an earthen floor, would be one of the best decisions you could make with this house.
 
Queenie Hankinson
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Assuming the earth is free--the cost to build a 1500 sq foot earth bag home breaks down as follows:

Barbed wire approx 1000.00
polyethylene mesh bags--1700.00 look up plyethylene bags, 450.00 worth builds a 900 sq foot home.
scrap wood for window and door framing (donated FREE but if bought) approx 450.00
bond beam (poured cement) 1200.00
2X10s for shed roof---20 (16 on center, 14 feet long) retail--360.00
plumbing piping--500.00
windows and doors including hardware and casing-- 2000.00
quik crete for cement base (a lot of people use bags and simply put in place) 500.00

lighting, electrical--1000.00

Lindseed oil for floor (or can make clay tiles) --100.00

Insulation for roof--500.00

chopped straw for cob (clay on site) --100.00

quick lime (100.00)

Wheel barrel---115.00 (new at Lowes)

Tampers (made--2 of them) 200.00

Roof decking--600.00

chicken wire mesh (not necessary because using mesh bags for fill dirt)

Misc--1000.00 (for incidentals)
_____________________________________________________________________

Less than 15K. I can make it cheaper --homes can be built for about 5-7K in the US and in the US if you use the mesh poly bags you do not need barbed wire or chicken wire especially in the dryer Southwest. Not sure why you think it would cost so much more unless you plan on also excavating and pouring a concrete stem wall or basement/foundation.
 
Queenie Hankinson
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Justin: cob is a breathable coating--use on walls, not on floor--the straw in cob BREATHES within the clay substrate which is why lime plaster as opposed to gunnite or any other sprayed on stucco is used to seal and final coat cob structures--to continue to allow for breathability. The walls will absorb and wick moisture but the permeability and breathability will allow the wall to dry out as the water evaporates through the wall.

Not with a floor--water CAN puddle and deconstruct. Without firing, clay can revert to mud under adverse and continually wet conditions. If you wish to have a dirt floor --seal it with oil after firmly pounding (tamping) the dirt until compacted and wetting it, then apply linseed or another sealant oil, let it cure--apply again--let it cure--if you like, apply again. OR make adobe clay tiles from the clay soil.

If a WOFATI home costs you 25K or more, then it is NOT cheaper than an Earth bag home--if you use the mesh bags as opposed to the smooth Cal Earth bags--you do not need to use barbed wire or chicken wire.

In Siberia, it may be worth your while to use a solar water heater, run pex lines beneath the floor (for warmth and passive solar collection in the winter) then apply the dirt over that to about 4-6 inches, pressing very firmly then applying oil. I have helped to build and repair cobbed homes as well as pounded floors--for warmth, it would pay to add insulation to the earth, and again, I believe if you have the right ratio of clay and sand on site, you will come out far cheaper with an earth bag home as opposed to any other kind --if you berm the back and ensure protection from wind on the northern side (or your country's coldest side) you will be more energy efficient also.
 
Queenie Hankinson
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For passive solar heating and minimize thermal loss--consider a trombe wall in front of the windows (or a trombe knee wall) after painting the barrier black, and allowing for venting, the collected solar heat during the day is released via an internal wall vent into the home in the winter and released to vent out if needed in the summer. Trombe walls take advantage of thermal mass and solar energy via windows when constructed correctly, another possibility is to make solar chimneys to create warm or cool air circulation via air flow.
 
Queenie Hankinson
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Justus (sorry for calling you Justin) consider an earth mound home--very cheap--if on a hill just cut in the sides and back then build a front--if not--you can construct a hill--pile up dirt to a height of 15feet, pounding it down , if you can pay for an earth moving machine to do this it takes just a few hours, Make sure the mound is as long as you wish your home to be --and it has to be COMPACTED with the back side facing the coldest, windiest area. After the mound is pounded down, an excavator carves out your living space in a "U" shape and you then buy the material of your choice to build the only outside wall (the front--the sides and back are a huge thermal mass which stays ambient, often around 52-62 degrees Farenheit.

If you like, make the entire front glass or significant areas glass--each room is one room deep --after it is carved out and you frame and build the front, the most expensive things will be plumbing, electrical, and any dividing walls you wish to make on the inside--largest expense will be the roof and the excavation and pounding--the total cost should be less than 15K --(in the US) use a membrane roof and decking then plant sod on top--very cosy, very inexpensive and relatively quick to do--will be like a rammed earth home but at much less the price--if you are allowed to live in a hill that is.
 
Queenie Hankinson
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Justus--you do NOT want to use a cement coating on an earthbag home unless you live in the desert.The reason is that an earth bag home is sealed with a cob plaster and so much breathe and allow water vapor to escape-- those who live in humid climates or anything short of arid climates often end up with slumped or failed earthen walls or worse, bad cases of mold which is what happens when concrete wicks up moisture but due to the concrete wall coating, the moisture cannot escape, it then builds in the wall and the straw within the cob can get wet and mildew and mold which then requires you to tear your wall out or be deathly ill. Cob needs a breathable plaster due to the straw and also clay content is important. Walls sealed with concrete plaster often fail because the natural components of cob combined with environment and the wicking nature of cement then the sealing nature of cement plaster do NOT mix.

If you use cement, look for cracks and the mold problem within the first 3 to 5 years.
 
Kevin EarthSoul
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Queenie,

I really like your mound/earth berm home idea with a trombe wall. It's what I have in mind. As for the dividing walls, I was thinking of building sturdy, load-bearing earth-bag walls between "cells" that would support the heavy living roof. I'm wondering if you have looked into using PAHS with such a design. If an artificial hill is created, it could be easily covered in an insulating material, such as a layer of scoria rock, before the final membrane and sod are laid on. Also, sealed barrels of water could be buried in the hill, adding thermal mass for the passive annualized heat storage. It would also make it much easier to lay in earth tubes.

Kevin
 
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