Content of the material
- Like what you just read?
- Try Out Cob House Living
- Base Estimates
- Cob House Cost Breakdown
- Why build a cob house?
- Healthy and Environmentally Friendly
- Artistic Design
- Energy Efficient
- Labor Intensive
- Legalities: Building Permits & Zoning
- FREE Tiny House Plans!
- Find your perfect design pro within minutes
- How long does it last
- Cob-Building Community
- Where to build
- Things to keep in mind while building one
- Cob Houses in Cold Climates: Important Note
Like what you just read?
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This 93-page eBook will instruct you, in detail, how to construct buildings with cob and earthen materials.
Learn about everything from site preparation, design, and foundations all the way through to the roofing and finishing work. Every major component of building a cob house is covered in this instructional eBook.
Try Out Cob House Living
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There are three main base materials used in cob building. Clay, sand and straw are mixed together to form cob. Now, if one had a lot of these materials already their cost would be small but the majority of people building today will need to at least buy the sand and straw to get their cob started.
The amount needed to be bought will be based on the scale of the building and the pricing of local resources. A cob home can be much cheaper to construct than a traditional home, though it is important to keep in mind the wiring, plumbing, windows and doors that will be used in the home. For our purposes here, we are just going to look at the base price for the cob construction itself.
Estimated pricing for 30 tons of clay, sand and straw can be rounded out to $500 apiece. Adding all three, the cob estimate comes to $15,000. This total is for a simple 1 bedroom, 1 bathroom construction that includes a living area and kitchen. Again, the prices depend on the area you live in and the suppliers that are available. Unfortunately, creating a static price list that spans the entire United States is not possible due to fluctuating costs in different areas of the country.
Cob House Cost Breakdown
I’ve kept close records of the costs of my building materials, and have determined that I have spent less than $3000 on building materials for the cob house. (I spent another $1000 on labor.) Here’s what I actually bought, and what I paid for my building supplies:
- sand (just over 30 tons total) – $507
- gravel (about 13 tons total) – $177
- straw (16 bales) – $36 (most straw I used was free)
- black walnut scrap lumber – $100
- misc. lumber – $20
- windows – $220 (two casement, one double hung window)
- electrical – $28
- galvanized wire – $30
- nails – $100
- raw linseed oil (for floor) – $72
- EPDM pond liner $622
- polycarbonate for skylight $400
and for the rocket stove:
- firebricks – $70
- flue pipe – $228
The two most expensive individual items are in bold. (Perhaps not surprising is that they are both part of the roof.) As you might imagine, many things are not listed because they were obtained for free – clay for cob, roof rafters, (hand harvested from our land and neighbor’s land), my large south window, urbanite for the foundation, etc. This is a very inexpensive house.
UPATE and an IMPORTANT NOTE: This house, as you might be able to tell, does not include a kitchen or bathroom. Basically, it’s a bedroom for one to two people at best. When I built this house, I had access to kitchen and bathroom facilities elsewhere. You can imagine that the cost of building would be much higher with those features…
The total cost of supplies for the house is $3000. If I included labor costs, the house cost $4000.
Why build a cob house?
Unlike conventional modern homes, a cob house is a simple way to build a DIY green home with little to no toxic materials. The construction style requires absolutely no building experience.
It’s straightforward and easy to learn how to build a cob house yourself with a bit of research from the many available books, YouTube videos, or hands-on workshops.
Even better, you can start building a cob house without any expensive equipment or tools. You use mostly inexpensive and free local materials—it doesn’t get more affordable than that.
Here are some advantages and disadvantages of building a cob house to consider:
Healthy and Environmentally Friendly
Cob homes are built almost entirely out of natural, clean materials. The main components come directly from the earth: clay, sand, and straw. Depending on where you’re building, these could come directly from your land; talk about hyper-local!
The building materials needed for cob homes lack both pollutants and environmentally unfriendly production techniques. Consequently, the carbon footprint of a cob house is exceptionally low.
Additionally, healthy air quality is naturally maintained because the structure “breathes” via its tiny pores. This keeps the air fresh, clean, and free of toxins—an ideal environment for those who suffer from indoor allergies.
From the start, a cob house is built strong. Straw is a crucial ingredient in the mix that acts as a natural rebar, holding the entire structure together as a solid piece. This makes it incredibly stable.
Minimal upkeep may be needed from time to time, but if adequately maintained, your cob home could last for centuries.
Another aspect of durability is the ability to withstand the elements and safety threats. Because of its porous nature, cob houses can withstand long periods of rain without weakening or weathering.
One of the top benefits of cob is that it is basically fireproof. However, other materials used, like window and roofing, may be flammable, but the structure won’t completely burn down.
Also, unlike wood structures, the cob mixture of soil, sand, and straw is not attractive to termites.
Earthen walls beautifully absorb sound, creating a kind of acoustic insulation. This keeps the cob house very quiet inside and out, blocking exterior noises and preventing noises from flowing between different areas of the house.
Let’s face it. The design of conventional houses is often unimaginative and dull. Cob naturally allows creative flexibility.
Because it can be sculpted into practically any shape, it lends itself to artistic, organic designs with beautiful detailing.
For instance, it’s easy to mold cob into curved arches and sloped ceilings, as well as creating built-in furniture, like shelves and benches.
Let your imagination run wild. You can create your unique version of a dreamy, romantic cob cottage!
View this post on Instagram A post shared by Sehn (@mossandmire)
Cob house walls are extremely thick, with 2-3 feet of insulation. So naturally, they have a high thermal mass that helps temperatures stay consistent and comfortable. They achieve this by absorbing sunlight which slowly warms the house throughout the day. This is known as passive solar heating.
Typically, a cob house uses approximately 20% less energy to heat compared with a typical modern home.
Most importantly, a cob house stays warm in the winter and cool in the summer. Though, one downside is that it can be slow to warm on very cold days without a supplemental heating source.
While relatively easy to build, it can be quite time-consuming. It takes a whole lot of mixing to make enough cob to build an entire house, even a tiny one.
The good news is, you can create small batches as you have available time.
Many cob enthusiasts say that it’s much easier and more pleasant to build with a crew. So it’s recommended to invite friends over for building parties to help share the workload while enjoying the process.
Legalities: Building Permits & Zoning
Currently, there has been no building code for cob in North America. That means no direct path for permitting and limited placement options. So most cob homes have been built under the radar, or on unrestricted land (no building/zoning requirements).
But a proposal for a model building code was recently approved in the United States!
Now an appendix for cob construction is being added to the 2021 International Residential Code.
While this must be adopted on the local level, it opens up doors to greater acceptance nationwide.
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Building homes with earth has been done since the beginning of time because of its widespread availability and versatility. According to , it was not up until the 13th century that cob homes were recorded to be used in Britain. In the late 15th century, cob houses became the norm in Britain and stayed that way until industrialization made it cheaper to transport brick and stone. Some older cob houses remain today have lasted over 10,000 years!
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The CobWeb Archive by Michael G. Smith and Ianto Evans
How long does it last
Cob was commonly used as a material for erecting homes in England in the 19th century, and some of those structures still stand tall. In fact, the oldest cob house was built 10,000 years ago during the Pre-Pottery Neolithic period in the Judean lowlands southwest of Jerusalem.
Get the cob mixture right, lay a good foundation, foolproof the roofing and apply a protective plaster, and strength of the cob house can be assured for years to come.
Thirty years after its founding, Cob Cottage Company has much progress to report. Evans, Smiley and Smith’s book, The Hand-Sculpted House, has sold more than 30,000 copies worldwide. Their CobWeb newsletter documents 18 years of experiments and advances (and failures) in cob technology, and it is available at the Cob Cottage Company. Multiple nonprofits, such as the Natural Building Network, continue to promote cob building and work with code officials to streamline the approval process. Every year, natural builders host regional colloquia to swap techniques and foster camaraderie. Some travel hundreds of miles and sleep in tents to help each other with projects.
Cob Cottage Company alumni are building and teaching all over the world. Despite the downturn in the global economy — or maybe because of it — cob workshops are more popular than ever. On her first building project, Ott’s most steadfast supporter was an unemployed single mother who went on to build her own cob house after her first home was destroyed by a hurricane. Together, they built a building while chatting and watching kids run around the yard. A construction site is not a playground, but without the noise and danger of heavy machinery and without nails littering the ground, a cob-building site is a great deal more family-friendly. Most natural builders go to great lengths to keep that atmosphere on their job sites. Many times I’ve been grateful for that as I watched my young daughters hard at work atop the growing cob wall of a friend’s new bedroom.
If you are serious about building with cob, Evans strongly recommends that you seek hands-on experience, either at a workshop or by volunteering on a project. To find a workshop near you, visit the event calendars on the websites listed in the resources box to the left.
Where to build
To be on the safer side, cob house should be built in moderate climate areas, as extreme climatic conditions require passive cooling or heating the interiors. That being said, it doesn’t mean a cob house cannot regulate the temperature on its own.
Depending on the content of straw bale/wattle-and-daub, a cob house can provide heat insulation or passive cooling.
However, a cob house is not advised for places with high flooding or natural disasters like hurricanes or tornado.
Things to keep in mind while building one
Although the disadvantages of building a cob house are few when compared to advantages, still they need to be considered. Always remember:
- Lack of proper ventilation can make a cob house humid on the inside
- Lack of uniform design may lead to problems with interior decoration
- It is quite a labor-intensive task to build a cob house
- Cob house can take quite a long time to build as each layer takes time to dry
- Extremely hot or cold regions might require temperature regulating equipment
- In some areas building a cob house may require special permits
Cob Houses in Cold Climates: Important Note
As it turned out, Gobcobatron proved to be a 3 season dwelling at best. Because the house has little to no insulation, it is not appropriately designed for the cold northeast Missouri winters. This house design is much better suited to extremely mild climates, including parts of the southwestern US.
I stress this fact to everyone I have contact with who is interested in building with cob. Please read this for the full story of my experiences living in a cob house in a cold climate. I heartily DO NOT recommend this. There are much better natural building solutions (including straw bale) for cold climates. Well hey, I guess the experience wasn’t for naught — I’ve been able to educate a lot of uninformed individuals about the importance of insulation, and the fundamental differences between thermal mass and insulation as a result of my personal experiences.
There ya go!