Content of the material
- What exactly is a cob house?
- Cob Pros and Cons
- Building A Cob House
- Set The Foundation For Your Cob House
- Build Your Cob Walls
- Windows And Doors In A Cob House
- Built In Cob Shelves, Stairs, Etc
- Sealing Cob Walls
- Seal Your Floors
- Can cob hold water?
- Base Estimates
- Try Out Cob House Living
- Advantages of Cob
- Find your perfect design pro within minutes
- Recipe for Building a Cob House
- How to build a cob house
- A checklist to follow:
- Why A Cob House?
- Cob Lasts A Long Time
- Cob Housing Is Affordable
- Cob Houses Are Pretty Fire Resistant
- Cob Houses Are Healthy
- Curved Walls And Round Cob Houses
- Advantages of a cob house
- Are cob houses safe?
What exactly is a cob house?
A cob house is made of soil, sand, and straw combined to create clay-like lumps. This simple combination of earthen materials is incredibly durable. Seriously.
The oldest existing cob homes are over 500 years old!
The walls are built up with lumps of damp cob mixture, then compressed, and finally sculpted into smooth, curved forms. Importantly, the cob dries to a cement-like finish, making it suitable for use as load-bearing walls, window framing, and even the roof.
One handful of the building mixture is referred to as a “cob.” This comes from the Old English term for “lump.”
The fibrous, mud mixture is also porous in nature, making it surprisingly resistant to rain and cold.
Like a living sculpture, the entire cob home often features artsy, curvy organic shapes for a whimsical look.
Cob homes can also closely resemble adobe-style cabins.
The CobWeb Archive by Michael G. Smith and Ianto Evans
Cob Pros and Cons
• Uses local, generally inexpensive or free materials • Can include creative, beautiful detail • Nontoxic • High thermal mass helps temperatures stay consistent and comfortable • Negligible environmental impact • Compatible with other natural materials (wood, stone, lime) • Fun to build with friends • Earthquake-resistant
• Labor-intensive • Needs additional insulation in cold climates • Will be unfamiliar to building code officials and insurers
Building A Cob House
A cob home has a lot of benefits, the one down side is that it’s very labor intensive and takes a good while. Unlike traditional houses which can got up very quickly, cob is a slow process, so be prepared.
Set The Foundation For Your Cob House
No house is any good without a solid foundation to build upon and that goes doubly for cob. Because your cob walls are so thick, around 24 inches thick, we are talking about a lot of weight. Literally thousands of pounds of weight from the walls alone. We want to have a good clear site to build the house.
Start by clearing the top layers of soil to get to the solid base layer soil. You want to dig down to below your frost line which can be 2-3 feet in some areas. From there build your base with quality materials and tamp down with a powered tamper as you build your way up.
Consider water flow, so that water will be channeled away from the house site and any water that does come to the house can drain away quickly. Use french drains and swales to handle this water.
Build Your Cob Walls
The walls in a cob house are super thick, which is what gives it’s strength. Your walls will be thicker at the base and get thinner as they rise. At the top, your walls might be around 18 inches, but your cob wall at the base will be 24 inches. As you build, poke holes int the top of the wall to allow you to integrate the next layer into the bottom layer.
In general you can only build your wall 2-3 feet vertically at a time before you’re going to want to let it set and dry some. This is an important step and is what takes so much time with cob. Allowing it to dry will make sure the wall doesn’t slump over.
Windows And Doors In A Cob House
You can absolutely have windows and doors in a cob house. The main approach here is to have a solid timber act as the header for the span of the top of the window or door. Basically have a big beefy piece of wood at least 6 inches thick and go for as wide as the wall.
You want the header to cross the gap of the opening and then extend at least one foot on either side so it rests firmly on the top of the wall, transferring weight onto the wall. The larger the span, the larger you need to extend your header to be supported by the wall.
Built In Cob Shelves, Stairs, Etc
Because you’re making the walls out of cob, you can form steps into the floor, you can have the cob flow so it has places to put books and other storage spaces. You are also able to have wood stoves, fire places and other cooking surfaces part of the actual cob structure.
This is where your creative side comes out and you can work in beautiful curves, artistic elements and anything else you can come up with.
Sealing Cob Walls
There are a large number of natural ways to seal the walls of your cob house. Various plasters, finished mud layers and white washes can all be used in the final stages of the walls. This helps seal the walls and keep them lasting a long time. It also lets you color the walls in artful ways.
Seal Your Floors
My favorite way is to do several finish layers of finishing mud and plaster. From there, 5-10 coats of linseed oil applied directly to the dirt floor. Finally come in and polish the floor with bees wax.
This approach brings a reasonably durable floor that is healthy from an air quality perspective, but also beautiful. There is something so satisfying as that finished waxed floor rests under your bare feet.
Can cob hold water?
“Will the cob be strong enough to hold all that water?” Technically yesbut that only goes as fare as just about anythingMay 12, 2015
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.
Try Out Cob House Living
Not sure if a cob house is right for you? Book a night’s stay in one Airbnb’s several cob rentals.
You can rent the below adorable cob cottage! It’s hand-sculpted using local, sustainable natural materials, and located on a lovely acreage with sheep, gardens, and orchards.
Advantages of Cob
Cob building is a very economical building material both financially and environmentally. This is because all of the materials used to build the home can be found locally, instead of having raw materials manufactured and transported to the building site. A three bedroom home could cost as little as £20,000 if you DIY.
A unique advantage homeowners get when they adopt cob building is artistic expression due to the fact that it is completely hand made. It is easy to add slopes or curves to any wall and you are not confined to the traditional building styles that we see today.
Cob houses create natural insulation and are very energy efficient. During the day the walls absorb the natural sunlight and store it until night, when the heat is released, this is due to its high thermal mass — meaning cob houses require little to no heating.
Little or no ecological footprint is left when it comes to building a cob home. The home is entirely recyclable and non-polluting, and for you the air in your home will be completely pollutant free. This is because cob is a porous material so air can pass freely through it keeping a healthy air circulation in your home at all times.
The wall are extremely strong and soundproof. They can even resist the impact of an earthquake, as well as being fire resistant. The straw, soil, and clay also repels unwanted pests like termites, rodents, and burrowing insects.
Find your perfect design pro within minutes
Here at Design for Me we match you with the right design professional, from thousands all over the UK. Get quotes & arrange up to three no obligation consultations. And it’s all completely free! Find out more here or get started below…
Recipe for Building a Cob House
With $3000 for supplies, $1000 for labor, and nine months of my own full time labor, I was able to build Gobcobatron, a small cob house with interior dimensions of roughly 15’x13′, and a footprint of (again, roughly) 20’x18′. Practically all of the labor was completed by hand (and foot), including making and applying all of the cob.
It’s true… you can build your own home with little money, but with lots and lots of time and enthusiasm. Even a small building is a big endeavor. And again, this is NOT your typical house, so please be aware of that fact as well! It’s basically a glorified bedroom, with no electricity or running water. This is about as bare bones as it gets. This house would not serve the full time needs of most people without access to amenities and facilities in another structure.
How to build a cob house
Building a cob house is easy when compared to other building techniques as it requires very basic construction knowledge. A bit of study about the right mixture of clay, sand and stray (depending on the temperature regulation requirements), a mud house can be erected.
A checklist to follow:
- Check with your local municipality about the possibility of building a mud house as some areas don’t allow construction of non-traditional structures.
- Choose a flat spot for constructing your cob house as it would be less labor-intensive.
- Come up with a construction plan for the structure.
- Create a solid foundation using cob or cement.
- Use your mud boots to mix the cob mixture for walls.
- Be careful while smoothening the walls so that they come out uniform and vertical.
- Add multiple layers of cob mixture for structural strength and stability.
Why A Cob House?
A Cob House is natural building material that has lots of beneficial properties that lend itself to a very comfortable home. With the thick walls of the cob house, you have a lot of thermal regulation happening. So in the heat of summer, the walls keep things cooler. In the cold of winter, the walls can carry heat late into the nights.
Cob Lasts A Long Time
Cob is also very durable if it is properly sheltered from the rain. A good roof will protect the walls and last for hundreds of years. Even when the house has started to weather, you can actually re-apply a new layer of cob on to the outside to make it brand new!
Cob Housing Is Affordable
Cob is also very affordable, in many cases all the materials can be found on your own land or can be obtained in large quantities for quite cheap. You’ll need to do a soil test on your own dirt to see if it’s suitable for cob building, but in general most sites have some usable soil.
Cob Houses Are Pretty Fire Resistant
Because it’s mainly clay and sand, you don’t have much for forest fires to burn up. Cob is a popular choice for areas that prone to wild fires or other extreme weather.
Cob Houses Are Healthy
Creating a cob house often creates a very healthy home for air quality. The one area you’ll need to spend some attention on is moisture levels. Once you make your cob, it will need to dry out full and that can take months to years. The bulk of the moisture will dry out of the walls in the first year, but will not fully cure for 1-2 years past that.
Once you build the house and add a roof, you should allow it to breath for many months before moving into it. Then I’d do your internal sealing process. When you do move in, a dehumidifier will be important to draw the large amount of moisture out of the air.
Curved Walls And Round Cob Houses
The thing I love most about cob houses is the curves of the walls. There is something so cozy, so appealing, so comforting about the curves in a cob house. You can have these organic forms that allow elements just flow into each other. It is hard to put your finger on exactly what it is about cob houses, but they have this magical quality that seems to resonate with some part of our brain. I love it
Advantages of a cob house
- They are breathable and have no dampness inside
- Carbon footprint of a cob house is almost nil compared to concrete buildings
- Demolishing a cob house has minimal impact on the environment
- Aesthetically beautiful as they merge well with the surrounding landscape
- Affordable due to the low cost of material and construction
- Energy-efficient due to natural temperature regulation inside
- Built from locally sourced natural building materials
- Creativity and flexibility in building due to moldable qualities
- Extremely durable and solid due to the use of straw in cob mix
- Termite proof, fireproof and earthquake-proof
- Free from toxic emissions, thereby maintaining the oxygen-nitrogen levels of the soil underneath
- Acoustically optimized due to sound-absorbing properties
Are cob houses safe?
Since soil is used as the base material for the building it is almost completely fireproof and termite-proof. This makes cob house one of the safest DIY homes that one can go for.