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Questions on building a cob house  RSS feed

 
Lynsie Overton
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For a few years I have been researching cob houses, thinking of designs, and gathering "references" as to what kinds of things I would like to incorporate into a cob house.
Today I am wanting to try and find some rough estimate as to a general cost of certain things.
I am wanting to build one that is 600-800 sq ft., probably all on one floor, but considering building upwards and perhaps having the square footage split between upstairs and downstairs.
The specific costs I am wanting figured out are listed below.
Finding answers to a lot of this stuff on Google hasn't been the easiest.
So here are my 3 questions:

1.  I want to have have solar power, that way I can still use my electric devices easily. Ideally I would need 1-2 outlets in each room.

2. What is the best way to get water to my sink, shower, toilets, etc., and what costs would be involved? I am really interested in a rocket mass heater for warming a bath tub, but am unsure if I could get it permitted to build. I am wanting to have 2 toilets in the household, as well as a tub/shower combo in one of the 2 bathrooms.

3. I have read that cob houses are good at keeping the heat out for the most part, but where I live it is often 100 degrees for a good portion of the summer, and then drops down into the negative temperatures in winter. Will portable A/C units suffice in the summer instead of having to get air installed, and will fireplaces or similar work in the winter? The weather here is really quite odd. IF I do require heating & cooling installed in the cob house, how much will it cost given the square footage I am wanting?

Thanks!
-Neon
 
Mark Tudor
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Location: SoCal USA
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How many people will be helping you build? Also assuming you have tested your local soil and it contains the proper levels of clay and sand? If doing this solo, a 20x30 structure is pretty big for cob, and takes a LOT of cob, which takes quite a while to build. Have you picked up and read The Hand-Sculpted House? The book is excellent on covering all the various aspects. You can also go visit the author in Oregon as they have workshops and work parties, http://www.cobcottage.com/ has more info. I'm scheduled to go there in October to do a workshop and work party to literally get my hands dirty and learn more.

They highly recommend working out how much space you really need and making the place as small as possible at first. Rounded spaces feel bigger than they are, no wasted corner spaces so your footage is lower. Reconsidering things like 2 bathrooms in just 800 feet could be part of that.

If you build the roof overhangs the right size, your walls will be shaded from late spring to early fall, so the sun isn't heating the walls during hot weather and hopefully you don't need any AC and all the additional costs for running it off grid. But in winter the sun is lower in the sky and can hit the walls and if positioned properly to the south the sun also hits a masonry floor to help passively heat the space, and at night radiates that heat. A rocket mass heater that gets winter sun but no summer sun works the same way, absorbing heat to give off at night. Can you plant some trees like black locust that you can coppice to provide renewable firewood for the RMH? If yes then after a couple years of initial growth your heating costs just your time to cut wood. Otherwise there's no way to say what anything will cost you.

You can add solar and the various components to a cob house, just need to calculate your power needs to determine battery storage and pane sizing to properly charge, there are web sites with those calculators. You can plumb water and power under the floor and come up where you want fixtures, then finish the floor after that. Is your water gravity fed, pumped from a well, or city provided? That would affect what you do/need too. You'll have to come up with a bunch of specifics on design to determine what you can do and what it will cost.

Good luck!
 
Daniel Ray
pollinator
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Location: Stevensville, Montana; Zone 4b
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Hi Lyndsie,

While 600-800 sq. feet is sizable for a cob house, it isn't impossible. Remember that building up saves money, so putting in  a loft will greatly reduce your costs. The most expensive part of a house is the foundation and the roof. Since you live in an area that hits negative temps, you will need to spend more on insulating the roof and digging a deeper foundation.

I also recommend heading over to www.cobcottage.com for information. If you call or email them they are extremely helpful.

1) solar is just as easy to set up on a cob house as a conventional stick built

2) Plumbing is similar to a stick house, but you need to plan where those pipes are going to enter and exit through your walls. Normal houses can run pipes within the walls, but cob makes this a bit more difficult. Make a map, but even for a larger 800 sq. foot house, it shouldn't cost much. It all depends where you are buying your materials and if they are new. Used parts are extremely cheap.

3) I live in a 350 sq. foot cob house and in the summer the house doesn't get over 80 degrees even with weeks of 90+ weather. I will say that an A/C unit would need a nice sized solar system to run it for any period of time. Rocket stoves are extremely efficient, but I can't speak to the heating water for a tub, there are a lot of threads on permies dedicated to that train of thought. I really doubt you will need to cool your house in the summer, but you will definitely need to heat it as the cob really doesn't perform the greatest in sub temps.


Finally, I suggest researching balecob technique for your house as it increases the speed, ups your insulation, and greatly reduces the amount of cob you need to make. Cob Cottage Company recommends this technique for our regions with high temp fluctuations. There is not a lot of info on this technique, but Cob Cottage will answer any questions. I am currently building a similarly sized balecob house in Montana. For cost comparison our house is roughly 800 round feet with a metal roof, half loft, compost toilet, solar system, on a rubble trench foundation and it is costing between 15-20 thousand.
 
Bryant RedHawk
garden master
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Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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For a two story house, the ground floor will need timber beams to support the floor and that second story, timbers are traditionally rather costly on a linear foot basis, For the weight of the cob you would need 6 or 8 inches wide by 10 to 14 inches deep timbers.
The ground floor walls would need to be a minimum of 24 inches thick and taper up to the second story top which would need to be around 12 inches thick.
The books mentioned are a great way to actually get into the physics and engineering you will need to have a grasp of to get it right, no one wants their house to fall down around them or lean over then collapse.

Redhawk
 
Rebecca Norman
gardener
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Location: Ladakh, Indian Himalayas at 10,500 feet, zone 5
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Bryant RedHawk wrote:For a two story house, the ground floor will need timber beams to support the floor and that second story, timbers are traditionally rather costly on a linear foot basis, For the weight of the cob you would need 6 or 8 inches wide by 10 to 14 inches deep timbers.
The ground floor walls would need to be a minimum of 24 inches thick and taper up to the second story top which would need to be around 12 inches thick.
The books mentioned are a great way to actually get into the physics and engineering you will need to have a grasp of to get it right, no one wants their house to fall down around them or lean over then collapse.
Redhawk


I'm confused. Don't the second floor walls have to be exactly on top of the ground floor walls, so the timbers do not take that weight? (That's how we build in Ladakh, and I consider it a basic principle of designing houses here)

I've lived and worked in earthen buildings for over 20 years, and our old-style rammed earth was similar to cob in its composition and density. Our best building is the one with ground floor walls 2 feet thick and upstairs walls 1.5 feet thick. We heat it only with passive solar, in a climate with 5 or 6 weeks of pond hockey and a minimum of -23C most winters. I'm sure with American roof insulation and windows you'll be able to, though we are in the desert at only 34N so you might not have as much solar gain in winter. In this climate AirCon is not generally needed or wanted, but anyway our building is cooler than outside when it's hot in summer.
 
Bryant RedHawk
garden master
Posts: 3132
Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
253
chicken dog forest garden hugelkultur hunting toxin-ectomy
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In the USA there are now codes that deal with cob houses as well as other alternative building methods, this makes restraints on how you build.
Building any two story house requires the upper walls be plumb and square to the first story walls, the timbers give strength and a solid floor support.

In England, Scotland and Ireland there are cob houses built this way that have been standing for over two hundred years. Wide eaves keep the rain off the plastered exterior walls.

Thick cob is a great heat retainer and excluder so little wood is needed in the winter time and little cooling is needed in the summer time. This is mostly dependent on the humidity values the region experiences.

It would be very possible to heat such a home with an RMH or wood burning stove (maybe two depending on the design of the house).


Redhawk
 
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