Cob Houses: A Beginner's Guide

by Tessa Hobart | LAST UPDATED August 20, 2021

A cob house
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Cob is a natural building material that’s seen quite a bit of use over the years. History buffs will probably know that some cob buildings are still standing, dating back as far as a few millennia. Presumably, this was one of the first building materials ever used.

We’ll get into the specifics of what cob actually is a bit further in the article, but the simplest way to explain the material is that it’s a mixture of dirt, water, and straw. While this mixture doesn’t sound like it would withstand a light breeze, let alone being used as a building material, the actual sturdiness of a cob cottage may shock you.

Cob houses have quite a few benefits that people don’t know about, and we’ll do our best to go over all of them in our article. We’ll also go over the disadvantages, the building techniques, the mixture ratio, and pretty much everything you’ll need to know before you start working on your cob construction.

Off-Grid Living

Because of the eco-friendly nature of the construction materials, cob houses have become quite a popular house option for a lot of off-grid enthusiasts and nature lovers.

Cob houses are pretty much the only construction that can be made out of purely natural materials. So you won’t have to use rebar to enforce the walls unless you want to. Everything from the bedframe to the windowsills can be made out of wood or other natural materials, and the carbon footprint of the entire construction will be so low that it’s practically non-existent.

Off-grid enthusiasts also find a lot of appeal in cob houses due to how easy they are to build and live in without even having to think about using contractors or companies. Not only will this save you a lot of money in construction costs, but it’ll also allow you to create a home that’s built by you and just perfect for your needs.

Utilities

Since we mentioned how perfect cob houses are for eco-friendly living, many people assume that this means that they can’t have basic utilities in their cob houses. The truth is, nothing is preventing you from trying to hook up all of the standard utility lines to your cob house, but you’ll need a bit of help.

To set up power lines and water pipes, you’ll need to know exactly where they go and how they need to be set up. This requires a lot of planning and expertise, so if you’re not a veteran in this field, you need to hire a professional or engage a construction company that can create the full layout for you. 

In addition to this, you’ll also need to hire a plumber and an electrician to set everything up. The price of these services varies depending on the scope of the project and the time needed to complete it. Luckily, since a cob house isn’t exactly going to be a massive construction, they’ll likely finish pretty quickly, and you won’t take much damage to your bank account.

Advantages

Bricks of a house

There’s a lot to say about the good points of cob houses—their style, the advantages that come from using that specific material, durability, and so on. However, to keep our article as concise as possible, we’ve narrowed down all of the good points of cob homes into three specific talking points.

Low Cost

Aside from your time and effort, your necessary resources are limited to just a few straw bales and the initial construction plans. While other houses are built on the property, a cob house is built out of your property.

All of the dirt and water you need to create the material is already present in your yard, and the only missing ingredient (the straw) can easily be found and purchased. The small bales over a meter long can be purchased for around $5 apiece, while the large round bales that you sometimes see in the middle of fields go for between $40 and $90.

Aside from the price, all you really need to consider is the amount of dirt you have at your disposal. However, as long as you don’t dig up the entire top Earthen layer, you should be fine when it comes to soil.

All in all, considering that all of the materials are already at hand and the necessary tools are basic, we’re pretty confident in saying that this is without a doubt the most cost-effective way to build your own tiny house.

High Thermal Mass

Cob works are well-known for their excellent heat retentive properties. This is the primary reason why many people still prefer to use cob ovens over the more technologically advanced alternatives.

Most cob houses have walls that are at least 24” thick at the bottom, and while they do get thinner as they go up, they’re still at least 15” at the top near the roof. This cob house characteristic ensures that most of the heat generated within these thick walls stays inside.

Additionally, a lot of cob houses are also built in the form of a circle and have one rounded wall that encompasses the entire living space, as opposed to 4 flat walls on each side. This will allow you to install something like a rocket mass heater, which is known for being pretty energy-efficient, while also properly warming up any space in a line of sight around it in a matter of minutes.

Even if your cob house is a traditional square shape and your walls aren’t quite as thick as we said, the heat retentive nature of the material will still ensure that any stove or heater in the middle of the room can see you comfortably through any sort of winter chill.

Your Own Cob House

The one significant advantage to building your own home (as the disadvantages are many) is the freedom to do whatever you want with it.

There are a few building restrictions that you’re going to need to follow, but for the most part, you can make your house exactly how you imagined it. That will also allow you to make a house that has all the spare room you’d need as well as the exact layout that you’re looking for. The fact that you’ll be able to make this with your own hands is also a bit of a “stick your chest out” moment since you can take pride in the home that you’ve made yourself.

Disadvantages

As with any building or construction material, cob houses have quite a few disadvantages that ke them less than ideal for certain people. In our opinion, these disadvantages aren’t a deal-breaker, but it’s understandable why they make the cob structures seem like they’re far from the best choice of housing.

Moisture

The biggest flaw we can think of when it comes to cob houses is the length of time it takes for the structure to dry. You can move in and start living in your created house pretty much immediately, but the cob walls are going to take quite a while before they’re fully dry.

“Quite a while” in this context doesn’t refer to days or weeks, but almost a full year. Cob structures are solid even when they haven’t fully dried, but, unfortunately, it takes them so long before they can be fully cured. 

Additionally, this also depends on favorable weather conditions and moisture buildup, which means that it can sometimes take up to a few years before your home can be considered complete.

Space

Natural buildings made out of cob aren’t exactly known for their mansion-like proportions. Making a simple cottage is already pretty difficult, so if you’re working on your own and without any construction experience, then it’s doubtful that you’ll build a two-story hand-sculpted house.

The size of the house will also dictate how much natural resources will need to be expended for the project. The larger the home, the more stability will be required for it to hold the roof up properly. This means scrapping your plans of only using natural resources and installing some metal beams for the support that’ll be needed, should you go high-rise.

In fairness, projects like these aren’t unheard of, and people like Kevin McCabe are famous for their large cob houses. However, if you’re planning on building something as large as what he has, then you’ll have to spend a lot of money and engage a few professionals like Linda Smiley and Ianto Evans from the Cob Cottage Company.

However, if you don’t have that much money to spare or if you’re planning to build a cob house on your own, then you’re likely going to be restricted to a modest one-floor construction with a joint living room/kitchen, a bedroom, and maybe an indoor bathroom.

Time and Labor-Intensive

The biggest issue when it comes to building your house on your own is exactly how much time and effort it’ll take before you can move in. As you might imagine, even if you know the proper building methods and you’re quite skilled at working with your hands, building a house from the ground up isn’t going to be easy.

It’s always a good idea to try and get a bit of help from your friends and family since doing this kind of project alone will take a good part of a year, even for natural builders. Unfavorable weather conditions and a busy schedule can extend the project for more than two years. So naturally, these are approximations.

Anyhow, even if you do manage to get a few helpers, you’re either going to need to take a few months off of work and work around the clock. The alternative would be to organize all of your “builders” and schedule them ahead of time.

Building Code

Building a house with mud and brick

There’s nothing illegal about building a house out of cob, or—more precisely—there’s no law mentioning that specific material. The problem is that this also means that there’s no step-by-step guide for getting a permit and no specifications that you’ll need to stick to during the construction process itself.

Luckily, all you need to do to make sure that your building is up to code is hire a construction company to draw up the initial designs for you. We’ve mentioned hiring a company to take care of the planning process a few times in our article by now, but luckily, this is the only stage of the process where outside professional help is nigh mandatory.

When it comes to building codes, the most important thing is the roof. As long as the officials are sure that the walls can support the weight without it leading to any accidents, then there shouldn’t be an issue with any designs you might have.

After the plans are drawn up, and the permit is granted based on the planned specifications, you’re free to start building.

Building a House

Now that we’ve gotten all of that out of the way, it’s probably time to get on to the actual construction process. Before we get started, we should mention that this article isn’t going to help you much during the construction itself.

We can tell you where to get started, how to mix the cob, and even what color roof you should get, but we can’t actually teach you how to put all of those materials together to make a house.

If you don’t have a background in construction or anyone that you can ask for help with, then the best thing to do is attend one of the many available building workshops that specialize in cob. You won’t be a licensed contractor at the end of one of those courses, but you’ll know how to build a small Oregon cob well enough to be able to live in it.

The mixture

The most important thing that you’re going to need to get right is the proportions of the mixture for the cob. Exact measurements are difficult to make, but you’ll need to mix in 2 parts clay, 1 part sand, and then add water and straw.

The earth that you use for the clay isn’t supposed to be the top layer or the wet earth that you find underground. What you’re going to want to do is remove the top layer of earth and use the next layer that’s just underneath it, which is often referred to as subsoil.

In order to get a good idea of if the mixture will hold, you’re going to need to make a small brick or a basic shape out of the cob and let it sit for a while. The exact shape of the cob figure that you make isn’t important since what you’re looking for is any slumping or deformities after you’ve put it in place. 

The mixture will need to stay moist, but it’ll also need to retain its shape, so you might need to add sand and water until you get it just right.

As for the mixing process itself, a lot of people prefer to use their bare feet and mix it all together in a container of some sort, while others like to use tools or even a cement mixer to get the job done.

The Base

Since you’ve already dug up the top layer of soil to get the necessary dirt for your cob house, you might as well keep going until you reach a depth of at least 3 feet. Mark out the size of the base and remove all of the loose dirt from the building site that you’ve just dugout.

Next, you’re going to use a tool to tamper down any remaining loose soil and proceed to fill out the hole to make the base of the house. The easiest material to fill the hole with is naturally going to be cement, but a lot of people prefer to use rocks.

Rocks are as good of a base for your house as any, but setting them up in a way that they’re level requires a lot of work, and you’re usually going to need to place them in cement anyway, so it’s a whole lot of work for nothing if you ask us.

The final thing that you’ll need to pay attention to when it comes to your base is the water levels. Ensure that any water buildup on your property doesn’t run towards your home since that could lead to major problems.

An easy solution to any potential flooding issues is simply raising the base a few feet off of the ground. As long as you have that much clearance and at least one strain somewhere close by, then you should be safe from any potential water damage.

When you build your walls out of cob, you’re going to need to expect there to be a lot of weight put on the base, so you’re going to need to make sure that your base is solid enough to withstand that pressure.

The Walls

Speaking of the walls, you’re going to need to build them in increments. The best way to bring up your walls is around 2 feet at a time. Then, once you’ve built up the walls all the way around the house, take a break before you start to add on to what you’ve already put down.

Cob needs to be moist for you to build with it, but putting too much material on wet cob could cause it to clump or collapse, so you should do it in increments of a few feet per day.

The exact amount of time you’ll have to wait before you add the next segment of the walls will vary depending on the solidity of the mixture and the weather conditions, but it shouldn’t take longer than a few days in most cases.

Additionally, due to the layering that you’re going to have to do, you might subconsciously start making the walls thinner and thinner as you approach the top. This is how most cob walls usually end up anyway, but it’s best that you try not to make them too thin, or they might crumble and break near the top when they’re put under pressure by the roof.

Sealing

Sealing your walls can help ensure that no dust or debris will come off and make a constant mess out of your floor. This is also a good way to ensure that they don’t start deteriorating over time.

Some people like to maintain the natural feel and simply use a thin layer of mud on the walls to seal them, while others like to go with more traditional methods and simply use plaster. Regardless of which method you go for, this will also allow you to decorate the inside of the house and add a layer of paint to spruce the place up a bit.

You also have the option to skip this step entirely and leave the walls as they are, but the entire process is quick, easy, and it helps preserve the walls a bit more, so there’s no reason not to do it.

Supports

Certain cob houses can stand on their own without any sort of support structure needed; however, the taller and wider you build a home, the more support that it’ll need.

These supports can come in the form of wooden columns on the side of the outer walls or a load-bearing beam in the middle of the house that can withstand the majority of the roof’s weight and ensure that the walls don’t have too much weight placed on them.

The support columns placed next to the walls are easy to set up. All you need to do is finish your cob walls and then add a few long beams on the inside of the house that goes to the roof. As long as you firmly affix them to the roof, wall, and floor, then they should remain in place.

A load-bearing beam is much more difficult to set up since you will need to be careful not to damage your roof by putting too much weight on one narrow point. As long as your measurements are correct, and the entire weight of the roof isn’t resting on top of the pillar, then everything should be just fine.

Windows and Doors

Both the doors and the windows will need wooden planks that can work as their support structure. The supports don’t necessarily need to be made out of wood, but regardless of which sort of material you pick, you’re going to need something sturdy enough that you can install a door and windows on.

As for the measurements of the windows and the doors, you’re going to need to check the dimensions of the models that you’re planning on installing and make sure that you plan the space out properly.

If you’re unsure of the exact dimensions, we’d recommend making the holes smaller than what you estimate the windows and doors need to be. This way, you can easily cut out a chunk of the cob to more fit the supports precisely since filling in holes that are too wide is a much bigger pain in the neck.

The Floor

When it comes to the floor, you can always add the same layer of mud or plaster that you used to seal the walls and simply polish it up with a layer or two of beeswax to give it that last finishing touch. 

Additionally, you can also simply get yourself some more traditional wooden floorboards and add a bit of wax to them as well.

The decision is up to you, and the only wrong decision would be adding no floor at all and simply living with a perpetual layer of dirt under your feet. But, you know that already.

Conclusion

Building a house with mud and brick

There are places in England and British Columbia where people actually rent out cob vacation homes, and New Zealand has even made them in the style of hobbit holes. Unfortunately, these vacation homes usually aren’t cheap, and people still prefer to rent them out instead of going to a decent hotel with room service.

This shows you that there’s a lot of interest in these simple DIY housing options, but whether it’s just a novelty or an actual lifestyle choice will depend on the person.

We believe that there’s a lot of merit to owning a cog house, but the ultimate decision on whether you want to live in such a structure, or if you wish to have it as a vacation home is up to you.

Tessa Hobart
Tessa Hobart moved into her first tiny home (a trailer in her uncle's backyard) when she was 19. Without giving away her age, she now has many years of tiny home experience and is currently designing an A-Frame as a second off grid home. She lives with her husband and enjoys card games and mountain biking.

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