Cob Houses: A Simple Guide To Building A Cob House

Even though I am busy building my own tiny house, I still find myself thinking about building a cob house… is that cheating on my tiny house?

cob houses

I have been coming back to cob houses again and again because I love the curves of cob walls, the organic feeling that the cob mix brings and the price is also very attractive.  I have thought about building a cob house if in the future I decide I need more space if I get married or just want more space.

 

What Is Cob?

Cob is basically clay, sand and usually straw mixed together to be used as a building material, kinda like bricks, but the advantage is that most of the materials can be sourced on site or purchased cheaply.  Having the right ratio of these three ingredients will let you create a study mix.  It’s basically like mud castles for adults, that is a building technique that’s been used for over 10,000 years!

Why A Cob House?

why choose 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!

simple cob house with lots of natural light

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 house with arched roof

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.

interior cob walls of house

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

How Do You Mix Cob?

how to mix cob the right way

The important part of cob is getting the mix right, you want roughly between 2 parts clay, 1 part sand, sprinkling of straw and a little water.  To mix these together the favorite method is with your bare feet!  I love the feeling of the cob squishing between your toes, so much fun!  You want the ingredients to be very well mixed, moist, but not wet and the straw well worked in.

The mix should hold its form solidly and not look like its melting or slump.  Make a test set of brick and allow them to dry.

Building A Cob House

building a cob house step by step

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.

cob house foundation

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.

layer of cob mix to create a cob wall for the house

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.

install of windows into a cob house

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

plastering 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.

bees wax sealed cob floors

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.

What Can Cob Be Used For?

Cob is a great multi purpose building material.  Basically, most of what you’d normally build into a house, you can also build out of cob.  Cob has been used for thousands of years, so we have learned a few things about how it can be used in various way.  Here are a few of the big ones:

Cob Structures

Obviously cob can be used to build a house out of, but it’s also good to make other elements.  In the distant past, this was the building material of choice, so barns, well houses, out buildings, animal pens and storage buildings were all made out of Cob.

Cob Ovens

My favorite use of cob is building cob pizza ovens… because, pizza.  A cob oven can get to 800 degrees and is key to making a really good pizza.  It’s also really good for baking breads.  The oven is able to have a very consistent heat that also has some moisture to it.  This is way better than your home oven that has wild heat swings.

me building cob oven

Typically what I’ll do is get the oven heated up full, then put a little door on the front to let the heat fully soak into the mass of the oven.  From there I’ll stoke this a bit, then clean the bottom floor with a wet rag, making sure the coal bed is pushed to the back of the oven.

From there I’ll cook my pizzas which can fully cook in as little as 30 seconds!  I’ve been able to raise my small cob ovens up to 800 degrees for really fast cooking times that make delicious thin crust pizza.

After pizzas, I’ll toss in a few loafs of break to bake as the heat starts to tapper off.  I don’t add any wood, just let the heat bleed off, which it will still be around 500 degrees at this point.

Finally I pull the bread and slide in whole chicken, a beef roast or other large meat with vegetables.

Rocket Mass Heaters

A rocket mass heater is just a high efficiency wood fire that the heat is piped through a large mass of cob and sometime rocks.  The cob will heat up and the larger the mass of the cob, the better.  This is usually done as a cob bench, which allows you to have a useful large mass in your house.

bench in a cob house with a rocket mass heater through it

 

Cob House Tours

Here is a collection of some of the best cob house tours I’ve seen.  Take a look at these video tours:

Cob Design Inspirations

One of the wonderful things about cob homes is the ability to have a lot of artistic flair to them.  The natural curves of the house are one of the best features of cob homes.  Here are some photos for you to get some design ideas for your own cob house.

Cob house interior

Cob houses can be big and 2 stories

cozy bedroom in cob house

use a rocket mass heater to heat your cob house

organic shapes for handmade cob house

natural curved cob stairs

Cob house interior with wooden beams and stone floor

cob house exterior

5 Comments
  1. Hey, one of those places is my neighbour’s house! It’s a fantastic place, very comfy and good in all weather. It was built before I got my place so I didn’t get to see the process but I’ve heard lots of stories. If I was building a permanent structure I’d definitely consider cob, for both practical and aesthetic reasons. The heated cob bench is amazing on a chilly day.

  2. If you want a great exchange/apprenticeship go to
    http://www.dancingrabbit.org/
    and attend a stay building innovative cob houses,thermal mass rocket stoves,etc.
    Wonderful group of people!

  3. Ryan, I totally understand. I think about natural built houses all the time and we haven’t finished out the interior of our Tiny House yet! Natural built homes are so beautiful and we would have built this way had we had land to build upon & the money to buy the land (we decided not to go in to debt again and opted for the tiny house on wheels instead).

  4. What do you guys think of a tiny cob house on wheels? So building a cob house on a trailer? Do you think it would crack going over a speed bump? I really really want to do this but haven’t found any information about cob houses on wheels … is it too heavy? Thank you for your input!!!

  5. I love the Cob house. Am building in franklin tenn do you have plAns for your cobs? Lovely

    Genie akin

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