How to Build a Better Outdoor Pizza Oven

by ziggy on January 25, 2015 -- 22 comments -- Follow

Build a Better Outdoor Pizza Oven

Learn how to build this outdoor oven in this new how-to

Several years ago, I wrote about how to build (the now-infamous) $20 outdoor cob oven. That oven I built worked decently, produced a lot of delicious meals, and advanced my pizza baking fever to new heights. Since then, we’ve built several more outdoor pizza ovens, and each of them has been a great improvement upon the original.

This newer model is slightly bigger, allowing for easier access to the oven interior, it has even more food baking potential, and the insulation is vastly superior. This sucker gets hot, and stays hot… for a long, long time. The oven has a small roof shelter, protecting it against the weather, and a chimney keeps smoke out of the face of the fire tender. Best of all… the oven is still very inexpensive to build.

This is a very achievable, low cost, and effective oven that will not cost you thousands of dollars to build. Here’s a look at the new and improved outdoor pizza oven plans and how you can build your own.

The Better Outdoor Pizza Oven Plans: Overview

Outdoor Cob Oven DesignThe oven I will propose and outline below is a highly insulated cob oven. For the uninitiated, cob is a combination of clay, sand, straw, and water. When dry, cob is extremely hard and durable, and highly capable of storing heat (given enough insulation.) The focus here is, of course, building with natural and recycled materials whenever possible. This oven is designed to be very inexpensive, consisting of materials that should be widely available.

The oven is no slouch in the baking department, either. With a 27″ diameter interior, you can comfortably cook two small pizzas at the same time while maintaining a small fire for cooking the toppings. We’ve made up to 60 or more pizzas in a cob oven described below, and they still cooked in 3-4 minutes after several hours of use. Needless to say, this sucker is very insulated. Not to mention, the range of other baking possibilities is vast — bread, roasts, pies, cookies, etc. are all fair game, assuming you have the gumption to prepare all those foods and harness the tremendous heat from the oven. This is much more than a just an outdoor pizza oven — this is a highly versatile, powerful baking tool.

Ok, let’s get on with the building plans…

Don’t Just Throw it Anywhere: Siting Your Oven

Siting your oven is an important consideration, and can make the difference between an oven that you rarely touch because it’s too far and isolated from your home or main kitchen, and an oven that creates its own positive space with ample room to prepare food for baking and to gather eager friends around for a big pizza party.

Questions to consider include: how close will it be to your existing indoor or outdoor cooking space? Will there be enough room to build around it later, if need arises for space to seat your growing posse of pizza-loving guests? How close is your firewood storage? What kind of shelter will you construct? Once your oven is built, it ain’t moving. These suckers are permanent fixtures.

Build a Sheltering Roof

If you live in anything but a dry desert climate, I am going to insist that you build a sheltering roof to protect your cob oven. Rain and moisture can quickly take a toll on an oven made of mud, and firing anything but a perfectly dry oven will be an exercise in futility — why spend more fuel and time drying your oven when it already takes a couple of hours to get the cob up to baking temperatures? An oven that continually gets wet will require a whole lot of on-going maintenance work, as well. It makes excellent sense to go ahead and build the shelter before you start the oven, too — this way you can safely protect your work while construction is happening. (It’s also difficult to do framing work around the obstacle that is the oven itself.)

Outdoor Cob Oven Shelter

The absolute minimum shelter I consider necessary for a cob oven is represented here — if you afford it, don’t skimp on protecting your oven

The absolute minimum shelter I consider acceptable for the oven I will describe below is about 7’x8′. (These dimensions are for the frame — the roof overhang will add another 2′ to each dimension.) This is what we recently built for friends, based strictly on the limited materials they had on hand. In an ideal world, I would factor in at least two feet of roof protection on each side of the oven, and additional space for a prep table to roll your pizza and bread dough, stage other food to be cooked, etc.

Local weather conditions will dictate how you design your roof, but the simplest solution is a lean-to shed roof with enough overhang to protect the oven and the frame itself. The options for a sheltering roof are literally limitless, and it can be as simple and austere, or extravagant and beautiful as you want it to be. Whatever you decide, just make sure the roof extends as least enough to protect the oven from blowing rain. Again, space for food prep is highly recommended as well. You’ll be much happier this way.

Dig a Drainage Trench

Cob ovens are extremely heavy. A foundation helps support the weight, raise the oven off of the ground to a comfortable working height, and should include sufficient drainage to protect the oven from freeze/thaw and other moisture damage.

To that effect, you need to go down before you go up. Start off by measuring a circle as large as your desired oven. My recommendation is a 27″ diameter oven. (Note: that means the interior cooking space is 27″.) For a 27″ oven, you’ll need a foundation much larger than that, however. Factor in another 8″ for the cob dome itself (4″ thickness around the entire sand form), 16″ for insulation, 3″ for plaster, and another 4″ for the diameter you may lose as your foundation grows taller and tapers inward. That’s about a 58″ diameter foundation.

Outdoor Cob Oven: Drainage

An 18″ deep gravel bed for draining water away from the oven site — daylight drain is pictured in lower left corner and covered with soil

You’ll want to mark out your desired size on the ground, and dig down, removing all the topsoil in place. Ideally, you would dig down as far as your local frost line, but you may choose to go less depending on what is convenient. If you don’t expect to have your oven around for the next 100+ years, it may be less important to dig that far down, and perhaps get at least 18-24″ deep to deal with 95% of all threats of freeze/thaw damage. (If you live in a southern climate, it may not even be a concern. Lucky you, in that case.)

Either way, dig a hole as deep as you deem appropriate, and dig a connecting trench downslope that will carry water away from the foundation. The trench should exit the ground at daylight, meaning the trench needs to be as long as necessary to be able to exit at the surface of the soil. Put a 4″ perforated pipe in there for the best drainage, or simply backfill it with gravel. The deeper you dig your hole, the further you’ll have to dig your daylight drain. The greater the slope on your land, the less distance you’ll have to cover. Make sense?

Backfill your new hole with gravel. Gravel is an excellent drainage medium. Any water that finds its way under the oven will fall easily through the gravel, and then be carried away from the site once it hits the bottom of the hole, and finds the daylight drain. Be sure to tamp every 6″ of gravel — don’t just dump it all in there at once! Tamping ensures that the oven will not settle in any unpredictable ways. You could also stick a perforated pipe under the oven to ensure optimal drainage.

Building a Solid Foundation

The foundation, as stated above, serves several functions. It’s also an opportunity to define the character of your oven. Stone is an excellent, timeless choice, either dry stacked or mortared. In areas without stone, brick or busted concrete (a.k.a., “urbanite”) make good alternatives. If you have a bunch of homeless cinder blocks around, that could work equally well, though they aren’t as attractive as the other options. Other options could include a wood crib, designed like a log cabin with notches on the corners and backfilled with rubble or gravel (but make sure the wood is insulated from the heat of the oven, in this case), recycled tires filled with busted up junk…. be creative.

Outdoor Cob Oven: Dry Stack Foundation

The start of a simple dry stack stone foundation

Cob Oven - Stone Foundation

A 36″ tall dry stacked stone foundation — this foundation represents quite a bit of material

We opt for stone wherever possible, and build up at least 18″, but preferably 36″. In cases where we don’t have enough stone to go the full height (more on that in a minute), the remaining height can be built up with cob. The stone is dry-stacked around the perimeter of the drainage hole, and filled in the center with all manner of crappy broken bricks and busted concrete. That stuff will never be seen again, so the center of the foundation is a good way to use your worst material.

Outdoor Cob Oven: Rubble

Junky rubble (broken bricks and cinder blocks, etc.) make for great fill in the center of the foundation

A 40″ height is a recommended average hearth height, so your foundation should be nearly three feet tall. (The hearth insulation and firebricks will make up the last few inches.) That ends up being quite a fair bit of material! Don’t underestimate how much stone or rubble you’ll need.

Outdoor Cob Oven: Completed Foundation

You can use cob to make up the difference in your desired foundation height, as seen here

Insulating the Cooking Hearth

Insulating the cooking hearth is crucial to taking full advantage of the blazing heat of your oven. You can use several materials, or a mix. We use either a combination of beer bottles and dry perlite, or straight perlite.

The advantage of using beer bottles is their wide availability, of course. Using straight perlite without bottles eliminates the need to “cap” the insulation layer with cob (which will leech at least some heat from the firebrick hearth). Perlite also offers excellent insulation values but is dusty and synthetic, and obviously more expensive than throwaway bottles. The choice is yours, however. I have not noticed a significant performance difference between using a bottle and perlite mix compared to straight perlite.

Outdoor Cob Oven: Beer Bottle Insulation

Beer bottles make for a very cheap method of insulating the firebrick hearth

A good 4″ layer of insulation is an okay minimum, though you may want to aim for a full 6″. (In my firing experience, 4″ seems adequate for the job. By “adequate” I mean that one oven we built with this method still demonstrated excellent heat retention in the hearth.) Build up a thin cob wall all around the perimeter of the oven foundation to contain the insulation material up to the height of your desired insulation level.

Note: If you did not use any cob to bring up your foundation height earlier, you’ll want to create a nice level surface with at least an inch or two or material prior to this containment ring step, as well.

Spread your beer bottles within the cob containment ring, and be sure that none are touching. The less they touch, the less chance something will shatter down the line. Once they are arranged, go ahead and dump your perlite, and please do make sure you are upwind of the dust!

Outdoor Cob Oven: Perlite Insulation

Perlite takes up the space between beer bottles

The next step can be eliminated if you use straight perlite: go ahead and use some cob to “cap” the insulation. Try to use as little as possible — an inch will do it. You should simultaneously create a nice level plane for the firebrick hearth. A trowel should help in establishing a smooth surface. Try your best to eliminate low spots — this cap doesn’t have to be 100% perfect, but the closer to level the better, of course.

Outdoor Cob Oven: Cob Cap

Using cob to make a thin, flat surface for the firebrick hearth — a trowel aids in smoothing the cob

At this point, I would wait until the cob cap fully dries before preceding. It shouldn’t take long with a day or two of sun and wind. If you don’t wait, you risk the chance of your firebrick hearth settling.

Build a Fire Brick Hearth

Fire brick is a block of refractory ceramic that is much more capable of withstanding high temperatures than typical red building brick. They range in cost from $1-$3 each brand new, but it’s likely you can find some used with a bit of searching. Check craigslist, or get in touch with local potters who may have some extra lying around from a kiln build. I’ve been able to get recycled bricks for $1, and new bricks for as little as $1.35 each. Be sure to get bricks that are at least 2 1/4″ thick, if not 2 1/2″. (That 1/4″ doesn’t seem to make a huge difference, but work with what you can get!)

Fire bricks make a lovely hearth capable of withstanding a very hot fire, and they store heat that will help bake your pizzas through the power of conduction. Laying them out is very simple, as they do not need any mortar.

Outdoor Cob Oven: Firebrick hearth

Setting the firebrick for the hearth, ensuring a level surface

Determine the center of your oven, and mark it with a scratch or twig. You’ll want your entire hearth pushed forward of center, as the “tongue bricks” should overhang the front edge by an inch or so. Using some sifted sand free of pebbles, lay out a thin, level bed for your firebricks. (You can run sand through a 1/16″ window screen to remove pebbles and larger particles.) You will need 18 bricks for your cooking surface, and another four for the tongue/door support. Line up and center the tongue bricks, and try to hang them off the edge by a good inch or so. (This will make it easier to hold an ash can under the hearth when sweeping coals out later.)

You can lay out the remaining 18 bricks as I did in the image above, or do 3 rows of 6 bricks each. P.S.: the reason 27″ makes a great oven size is that you are using the maximum surface area of the fire brick. Fire brick dimensions are 4.5″x9″, so 6 bricks x 4.5″ wide = 27″ wide.

When placing fire brick, be sure that you slide them downward into position. Do not get sand between the bricks. Use the butt end of a hammer to set them and to make tiny level adjustments. Your bricks should be level and flat — the flatter the hearth (meaning, no brick corners jutting up), the better your cooking experience will be. You don’t want your crusts or bread getting caught up on anything.

Don’t be afraid to start from scratch if need be — setting the hearth doesn’t take much time, and once it’s set, it’s set. There’s no changing things later.

Continue Reading the Better Outdoor Pizza Oven Plans

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  • Patty O

    I love the how-to and pics, Ziggy! I have one question: several years ago, I built a cob oven on my property in ME after taking a three-week course at the Cob Cottage Company in OR. I was so excited to get it going that I neglected to spend much time on the foundation. I am embarrassed to admit that I ended up buying concrete blocks from Home Depot – since I never mastered the dry-stacking method. Not using concrete between the blocks, they shifted pretty significantly during the construction of the oven. The foundation is now such an eyesore, and I am almost tempted to remove the roof, allow the elements to “dissolve” the cob, and start over. Do you have any recommendations for how to move/improve the foundation?

  • Thanks Patty!

    It’s honestly not much of a loss to start over if you’re that unhappy, I think. You can reuse the firebricks and most of the cob (just soak it in buckets), and probably improve upon your oven on the second build, too. Even without seeing it I can imagine it would be tough to try to change the foundation after the fact.

    April’s the better of the stone stackers between the two of us, I must say… I quickly lose patience for that particular process. But it’s true… stone does look much better if you have access to it!

  • how about useing a rocket stove as a heat sorce , and useing the oven as a bell , you’d need a fire proof door . The rocket J – tube would come in tru the floor richt next to opening of the door , and exit would be on the other side of the door in the floor of the oven, this way when the door is closed the oven would act as a bell keeping the hottest gasses in the oven and venting out the cooler ones, this would reduce the amount of wood used to heat the oven by 1/8 of what you are useing now . An other great advantage would be a cleaner oven floor and the ash still on the oven floor can be swiped in rocket stove

  • I’ve heard something like this described before, but have never looked into the designs. Perhaps it’s time for me to investigate!

  • Gerard Saunders

    Hello. I wish to build this but do not wish to build the shelter. Does the cob need to be exposed to the air? The reason I ask is because I am considering building my oven on a brick plinth, then extending the ‘walls’ up to above the dome and finishing off with a pitched roof covered in clay tiles. The cavity between the dome and the roof can then be stuffed with extra insulation. Any views very welcome, Kind Regards, Gerard Saunders, Battle

  • Hey @gerard_saunders:disqus: At that point, it sounds a little redundant… I’m questioning the two layers of insulation in particular. I think it would be better to have the dome exposed and figure out how to protect it with your brick and tiles, without stuffing that cavity with more insulation.

  • Gerard Saunders

    Waiting with baited breath for episode three of this! I’ve gone for sitting the oven on a slab which sits on a brick square. The front of the support is open and will be used to store logs.

  • Gerard Saunders

    Waiting with baited breath for episode three of this! I’ve gone for sitting the oven on a slab which sits on a brick square. The front of the support is open and will be used to store logs.

  • Julie

    Would a tarp work okay as an oven protector? Not ideal obviously, but as a temporary solution?

  • Temporarily, they’re okay at best… but I would still try to get a roof up first if you can!

  • Jim Schalles

    Ziggy ~Donkey has some photos of the rocket pizza oven they fired up at Sundog Natural Building in Mendocino last year. He told me if he did it again he would beef it up to an 8″ system as opposed to the 6″. I think the batch box rocket would be even more efficient for it. Its nice to stand by a clean burning earthen oven. Thanks for the write up on this, the web needed a good step by step with photos. (scroll down for the oven, although the lorena style cookstove is pretty sweet too)
    http://donkey32.proboards.com/thread/1301/all-adobe-mud-cookstoves-ovens

  • Carly

    Hello, I am hoping to build something like this for a community art project and I am just wondering if you have any kind of concise materials list or budget breakdown?

  • That’s a tough situation, since the integrity of the oven is dependent on the foundation, of course. Can you somehow creatively plaster over the blocks in an aesthetic way? Or maybe use thin stones as a kind of “veneer” over the existing concrete?

  • Hi Carly: I don’t have a concise materials list, and cost will depend on a few factors — if you are needing to build a shelter, and whether or not you can secure some of the materials for free (such as the clay, stone, sand, etc.) As far as material expenses go, though, you can generally do this kind of oven for very little money. Sorry I don’t have a more direct answer!

  • Sean

    One thing I’m curious about that has come up while planning my own oven: beer bottles are usually about 2.5″ in diameter. Where does the other 1.5″ come from in the insulation layer? It looks like in your picture that the perlite is only coming up to the level of the bottles so I’m guessing it’s not perlite? Any insights you can offer would be great. Also, thanks so much for this blog! It’s been indispensable while doing my own planning and building!

  • Thanks for writing, Sean. You can get 4″ of insulation with a layer of perlite (or even wood ash) under the bottles (and a bit on top, too). The insulation should be at least 4″ like I said above, whether it’s bottles + ash or perlite, or straight perlite. That means your hearth will stay nice and hot for a long time…

  • peter shear

    Ziggy, So for your dry stacked foundation you are just laying the stone down without any footer….directly on the gravel? That holds ok over time?

  • So far so good!

  • peter shear

    I am going to make a rock foundation with mortar…would you suggest just putting the first ring of rocks right on the gravel, or a footer?

  • Hi Peter: I put the rocks right on the (compacted) gravel. A footer is not truly necessary.

  • Angela

    Do you think you could put a layer of brick over the outside of the oven to protect it from the elements without causing any issue to the integrity of the oven itself? Or does the mud need to breathe? I have a lot of old used brick I was thinking to cover the exterior for protection.

  • Hi Angela,

    In this particular design, the light clay straw insulation would not support the bricks. The straw cannot support much other than a plaster finish. You would have to do a different type of oven to be able to use the bricks in that particular way.

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