What Is a Cob house? The World’s Oldest Building Material

What is a cob house? The world’s oldest building material is still popular. If you’ve never heard of a cob house, you will now.

Cob is a sustainable mix of stray, sand, and clay. Like adobe and other home building materials, its history dates back for thousands of years.

What Is Cob?

cob houseView in gallery

Cob, or clom, is one of the oldest building materials. It’s fire-proof and can withstand mild earthquake tremors.

The material is cheap but working with it requires effort. Think of it as nature’s concrete. Cob is eco-friendly and bio-degradable

History Of Cob

History Of Cob houseView in gallery
Gary Zuker

The term cob wasn’t used until the 1600s. But the material has been used since prehistoric times. The word cob is translated into “beat or strike.”

In Afghanistan, “tabya” means cob-work. The homes are popular in climates from New Zealand to Africa. Cob walls are two-feet thick.

With the invention of brick and other building materials, the popularity of cob faded. But in off-the-grid homes and third world countries, cob homes are built due to the available materials. 

The Difference Between Cob And Adobe

The Difference Between Cob And AdobeView in gallery
Artisan Builders

Many people confuse adobe and cob. Adobe and cob are different materials, but both are made with clay. But adobe is made into bricks and stacked together. 

Cob is a free-hand material, with each house sculpted. Both adobe and cob have middle eastern backgrounds. 

Large cob round house 1024x565View in gallery
Zero E Designs

Cob Pros And Cons

Every building material has pros and cons. Cob is no different. 

Pros of cob:

  • Artistic Expression – Most people who build with cob do so because they can truly express themselves artistically. Not only can you design your own house from a drawing, but you can create intricate patterns easily. 
  • Cheap – Cob may be the cheapest building materials available. You can’t buy it, but you can make it with materials found in your yard. Most farms will supply you with the materials you need for little to no cost. 
  • Energy-Efficient – Heating and cooling a cob home is easy. It insulated well, keeping both the cold and hot out. There’s a reason that it’s still used in desert climates and frigid climates both.
  • Water-Resistant – Cob is made with water, and after the cob hardens, it becomes water-resistant. Even during floods, cob homes can come out on top.  
  • Fireproof – Cob is fireproof. If you make your home with less straw and fibers then it truly is fireproof. This isn’t something that is true for most homes, especially those made of wood.
  • Earthquake-Resistant – Cob is one of the few materials that are earthquake-resistant. No fissure can disrupt it. The ground may break, but the home won’t be affected. 
  • Termite Proof  – Because the house is made of hardened clay, termites can’t, and won’t chew through it. The insects are drawn to wood and softer materials. 
  • Sound-Resistant – Although sound can get through cob, it won’t be loud. Cob is a great sound-insulator. To find out more about sound insulation, check out this article on soundproofing.
Large cob round house 1024x565View in gallery
Gary Zuker

Cons:

  • Takes A While To Build – A cob home isn’t likely to be built in a day. It has to be made, constructed and has to dry. It also needs to be put on in layers so it doesn’t fall or drip as it dries. So be in it for the long haul. 
  • Difficult To Work With – At first, it may feel like playing with clay or Play-doh, but cob isn’t easy to master. You may need to hire a professional to help architecturally, and even with the mixture’s ratio. 
  • Not Ideal For Cities – Finding the codes for building with cob isn’t easy. You’ll probably have to contact a realtor, contractor, or someone on the city council to find out what you need to know before building. 
  • Materials Not Always Available – If you do live in the city or a climate without much subsoil, then it may be difficult to build with cob. You need a lot of straw and a lot of subsoil. Getting some without disturbing the area may not be easy. 
  • May Need To Educate Yourself – Most contractors know how to build with stone, wood, or brick. But building with cob isn’t known by many. You will probably have to be the overseer on your project. 

How Much Does Cob Cost?

How Much Does Cob Cost?View in gallery
 Earthen Hand Natural Building

If you have the materials on your property, then cob can be free. All you need is good subsoil, water, and straw, or other fiber. For windows and doors, you can use recycled glass or wood. Some people even build thatch roofs. 

Since not all areas have subsoil, straw, and lime.  Here are the materials you may need to make cob and how much they cost to buy and deliver.

The subsoil costs between $2 and $6 per bag, A one-yard square will be $10 to $30. The expensive part of the soil is the delivery. You will pay around $150 to $600 per truckload for 10 to 15-yards. This means up to $50 a yard.

A large bale of straw costs between $50-100. This type of bale is around 4-ft long by 2-ft wide. You won’t need more than a few weeks, so the price won’t be much.

  • Water

Water is cheap. If you have it delivered, it won’t cost much. Worse case scenario, you pay a couple hundred for a delivery fee. 

You can buy granulated lime for $25 a ton, which is more than you need for any house. 

  • Labor

This is the most expensive part of building a cob house. 

Can I Build My Own Cob House?

Can I Build My Own Cob House?View in gallery
 SOM Land Design

The short answer is yes. Anyone can build cob. You can find the materials yourself, or at a friend’s property. 

Contact The City/State

Cob is an off-the-grid home. Before planning your new cob project, contact a local official to make sure that you know the codes. 

Create Plans

Draw up your plans, taking time to consider the practical side. It’s a good idea to have an expert look over them. But if you can’t find one, any architect can point out any red flags that you may not notice. 

Find A Spot

Finding a spot is difficult. Although cob is forgiving, the land needs to be flat. If there are a few hills, building a frame may be better. 

Lay Your Foundation

Many people prefer to lay a non-cob floor under the cob top layer. However, this isn’t necessary. You can create a cob foundation using boards to frame it. Remove the boards after the cob dries. The cob should dry before moving to the next step.

Creating The Cob

The exact mixture ratio depends on your climate. You want the cob to be thick, textured clay. You will probably want to stomp the cob. The water and soil go in first. You can mix that up well. Then, after you feel you have the texture you want, you can add straw and mix it in gently.

Forming Walls

Using one scoop at a time, apply the cob to the foundation where you want walls. You’ll need openings for doors and windows. 

As you add multiple layers, drill holes in them.  You might finish a foot or two per day. 

Windows And Doors

You can add the wood frame to the drying cob and install them as usual. Or, you can use recycled materials, like glass bottles, to create unique windows and doors. 

The Possibilities 

Large cob round house 1024x565View in gallery
Kali Natural Building – Eco-Friendly Architecture

The best part about cob is there are no rules. You can build shelves, closets, and stairs into your cob home. You can make holes for fireplaces or leave one, big, open room. This is your chance at an eco-friendly artistic expression.

Frequently Asked Questions (FAQ)FAQ

Is Mold A Problem In Cob Homes?

Mold is not a problem with cob homes. This was a popular misconception. Cob homes use earthen materials. What this means is cob homes are vapor permeable, so water can not get inside their walls. Without water and wood, mold cannot survive.

What Are Some Typical Problems With Cob Homes?

Typical problems with cob homes include industrial cracks and roof structure issues.  Cob homes do not have trusses. The walls will be pushed out by roof timbers. If the stone foundation shifts, the home will crack.

Can You Build A Tiny Cob House?

A tiny cob house is as a Hobbit house. The tiny home style is popular among homeowners who live next to forests. A tiny cob house has 300 feet of floor space. The homes don’t have electricity or wood stoves. Co homes use nearby streams for a water supply. 

Cob House Conclusion

A cob house is the ultimate eco-friendly home. Due to greater interest in climate change and eco-building, there’s a good chance cob homes could become popular in North America. 

As a sustainable building technique, the cob house might the best option. Those looking for a DIY home building project would enjoy creating and designing an original cob home.