Building a cob house: an eco-friendly dream home

Have you ever considered building a home with natural materials? It is, perhaps, the most creative and cost-effective option available. Natural building styles, like building a cob house, use sustainable, abundant, non-human-made materials. 

While this kind of home building has been around since the dawn of human existence, in modern developed countries it’s highly uncommon to build your own tiny house, let alone one built out of local materials.

Natural home building is seen as an alternative lifestyle choice. It is a liberating mortgage-free way of life for many. 

A cob house is just one of several natural building techniques available. It’s becoming an increasingly popular housing option due to its ease of construction, as well as low cost. And of course, the adorable look of the cob home designs!

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. 

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. 

Durable

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.

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Quiet

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.

Artistic Design

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!

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Energy Efficient

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.

Labor Intensive

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.

How Much Does a Cob House Cost? 

Looking for debt-free homeownership? Building a cob house is one of the best available options. Again, the primary materials needed (clay, sand, and straw) are quite inexpensive or even free. 

Many people have built beautiful cob homes for as little as a few thousand dollars.

But of course, the overall cost depends on what goes into your house, from windows to roofing. To keep your costs low, seek out recycled and salvaged materials. 

Of course, the most significant savings come from building a cob house yourself. If you hire out, the overall cost can triple due to the labor-intensive nature of building a cob house.

Your greatest expense will likely be the land you build on and any necessary infrastructure and utility expenses, from grading to installing solar power and septic systems. 

Importantly, the cost of land varies significantly by location, from a few to hundreds of thousands of dollars. Another cost-saving option is to look into building your cob house in an intentional community with like-minded residents.

How to Build a Cob House

The basic construction of a cob house is pretty simple. But before you can play with the cob itself, you must prepare your build site.

Begin by removing the topsoil, as well as vegetation from your work site. Then mark the perimeter of your cob house with pegs. 

During the build, while the cob mixture is damp, you don’t want to get it overly wet from rainy weather. So you need to dig a trench to encircle the structure to lead water away. It helps to backfill it with compacted gravel.

Build a Foundation

The incredibly massive cob walls are built on top of the foundation and around all plumbing and electrical lines.

Choose from a cement foundation or a dry-stacked foundation, made with reclaimed concrete chunks or stone. If you choose the latter option, lay your stones on tamped, solid ground within the trenched perimeter. 

Prepare the Cob Mixture

The cob mixture is approximately 1 part clay, four ­parts sand, and 1 part straw. 

For the clay, you can buy it or dig it up on your property—a great, but time-consuming option for saving money. Most soil is a mixture of some clay, some sand, and other materials. Importantly, you want the “subsoil” beneath the rich topsoil.

After gathering your materials, it’s time to mix. 

Mix water into clay and sand, and then add straw until it feels right. A little experimentation is needed to achieve the appropriate consistency.

The clay works best if soaked before mixing. When wet, clay particles expand and stick to sand and straw, binding it all together. 

There are two mixing styles:

• With power tools
• With your feet

The quickest, least labor-intensive mixing can be done with a portable cement mixer. While the cheapest, most fun ways is your feet or many feet. Invite friends over for a muddy dance party!

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For the foot method, lay out your tarp on a flat space. Spread a couple of layers of your dry ingredients on it.

Fold the tarp to begin mixing. It’s easiest with a person at each corner to lift. Do this a couple of times until the dry ingredients are thoroughly mixed. Then unfold and add water.

Next, use your bare feet to mix in the water and, eventually, the straw. Focus your energy into the heel of your foot to flatten the mixture like a pancake. 

Then use the tarp to roll the mixture. Repeat the process until it feels “right.” Ideally, the end result is a cob mix that resists being pulled apart. 

If unsure, you can test it by molding some cobs together and letting them dry for about a week to see how they hold up. It shouldn’t be crumbly. 

Build and Sculpt

Once the mixture is right, it’s time for the fun part—the build and sculpting process. Of course, you’ll need to build rigid walls, but don’t forget to get creative with the overall shape and details for your cob house. 

Break the mixture into manageable softball-sized balls, or little loaves of the material.

To build a wall, place a cob for the outside face, for the inside, and the middle. Smash and mold together. Continue this process until you’ve formed your structure.

As you work, use your thumbs to “knit” the straw fibers from one lump into the cobs surrounding it.

Or use cobbler thumbs, a wooden tool to stitch the cobs together, to work the straw into the layer below the new cobs and blend them together. Wet the surface before applying an additional cob.

Finish each cob layer by using your hands to create a clean, plumb edge.

It might sound tedious, but many DIY cob builders find it meditative.

Plaster

A standard lime plaster consists of 1 part lime putty, three parts sand, and a quarter-part fiber. Use cellulose insulation or straw as the plaster fiber. 

Mix the plaster by foot or paddle in a bucket or trash can for larger amounts. 

Then to complete the cob structure, apply at least two coats of plaster: one to even out imperfections and a finishing coat. When applying, use a firm pushing motion.

Seal plaster by painting it with several coats of linseed or hemp oil. 

Store any leftover plaster in a sealed jar for future repairs.

Maintenance

Over time, minimal maintenance of your cob house will be required. Scratches can be rubbed out with rough sandpaper then re-oiled. Additionally, any large cracks can be filled with plaster, polished, and once dry, oiled.

Cob House Plans and Building Resources 

If you’re serious about building cob house, check out this helpful list of resources:

• This Cob House: cob how-to guides, videos, and books
• Cobworks: cob workshops
• The Hand-Sculpted House: a Practical & Philosophical Guide to Building a Cob Cottage
• Building with Cob: a Step-by-Step Guide
• The Cob Builder’s Handbook

Spectacular Cob Houses

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.

If you haven’t rented from Airbnb before, use this link to get $55 off your stay!

Who are Cob Houses for?

Want to build an environmentally-friendly home? Building a cob house is a wonderfully affordable and easy DIY option for anyone looking to build their own green home.

Do you want to build a cob house? Let us know in the comments below.

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