Help me find flaws in my design!

[StockholmBaker]

Hello Forno Bravo, greetings from Sweden!

I am planning a barrel brick oven and would like some input on my drawings.
I have noticed dome ovens are preferred here but I think a barrel design would fit better for me. My biggest concern is that water will seep into the mortar and crack as it freezes (we get cold winters here).
I am therefor building a small “house” around the oven. Since the house is square, it felt simpler to have an oven with a square base. It would also require much fewer custom shaped bricks which I appreciate as I don’t own a good saw for cutting bricks. I have read that barrel ovens can take longer to heat up but that is something I can live with. The oven will be built at the summer house, so firing it will not be a weeknight event anyway.
Now to my questions:
1. Will the 2cm gap in-between the bricks at the top of the front arch be a problem? (see picture)
2. Is it a problem that one arch leans on top of another in the front facing wall?
3. Does it look like the oven will have good enough circulation?
4. Does the insulation need to be attached in any way or can it just be tucked in between the oven and the walls/roof?

Grateful for all the help I can get!

Best
StockholmBaker

[MarkJerling]

Welcome to the forum. I can think of no good reason to avoid the tried and tested dome design. But that's just me. I've never laid a brick before in my life before I started my oven and mine turned out fine.
Several others here have built rectangular houses over round ovens, so no reason that can't be done.
Good luck with your project!

Kind regards,
Mark

[david s]

Many folk, particularly new oven builders with no masonry experience, gravitate to a half barrel oven In the belief that it would be easier to build. In fact the reverse is true due to the combination of its inherent instability and thermal expansion, whereas a dome is a far more stable structure and preferred design for thousands of years and clever folk attempting without success to better it.
the outward thrust on the side walls of a semicircular arch are considerable and the thermal expansion tests out any instability. It can be countered by either buttressing or bracing.
A second issue is where the end walls join the barrel arch. Ideally the corners should be tied in, avoiding any vertical mortar joins coinciding, or at least the end walls built under the arch rather than against it. In addition the circulating atmosphere in a dome chamber is far superior, eliminating cool corners. The geometry of a barrel oven is however superior if it’s sole or main use is as a bread oven because it has higher internal sides at the outside of the chamber and more bread can be loaded into it than a hemispherical dome of the same floor area.
There are plenty of half barrel oven builds on this forum to research.

[StockholmBaker]

Hello again! Thanks for the replies!

My design is partially based on traditional swedish baking ovens (see pictures) which have been used for hundreds of years for different types of flatbread or "tunnbröd".

It is a good point through about the outward force the arch puts on the walls. Traditionally baking ovens here are built into a bigger structure, like for example the foundation of the house.
As my oven will be a free standing structure it will need some form of bracing. Do you know of any examples on this forum of correctly built arch ovens?

Also, regarding the back wall. I purpesfully placed it outside of the arch to allow the arch to expand/contract freely. What benefit would placing the wall inside the arch have?
The reference pictures i have found of old arch ovens (see picture) has the back wall placed outside of the arch.

Thansks for all the advise!
SthlmBaker

[david s]

My experience comes from kiln building where temperatures are around double and therefore also double the thermal expansion of an oven. However the same principles still apply. An expanding vault simply pushes out the end walls. If the only thing joining those walls to the vault is a continuous vertical mortar joint, expect problems, not straight away, but after many firings the expansion and contraction of heating and cooling will do its work of finding weakness in the structure. It depends on how you want to cook with your oven the barrel arch or large radius low vault oven is a good configuration for a bread oven, however, for an all round oven used for roasting, baking and pizza making the hemispherical dome which is self supporting and is a far superior combustion chamber, has proved to be the better solution for thousands of years.
I shall try, as hopefully other members will, to try and find you some good examples on this forum. Karangaidude’s oven is the first one that comes to mind.

[david s]

Here are some images from Daniel Rhodes Kilns (the kiln builders bible)

[StockholmBaker]

Hello again!
I can see how the bracing shown in the pictures you posted make sense in such a tall structure. The outwards thrust the arch places on the walls would easily topple the tall walls.
I plan on filling up inbetween the oven and outer walls with vermiculite mix, up about 3 bricks. Do you think that will be enough support?

Just looked through Karangai dude's oven build, what a beastly project! I don't think I have the know-how or resources to pull off an oven of that caliber, but I still got some useful insights!
In between the front of the oven and the arch holding the flue he uses a rope, made of what I assume is some form of ceramic fiber. This got me thinking, would it be possible to push some form of soft insulation, like a thin insulation rope or tufts of fiber in between the main arch and the back wall. Removing the mortar joint altogether, and essentially separating the structures and allowing them to move independently of each other?

Best
SthlmBaker

[david s]

You are correct, the higher you go the greater the problem. It’s what led to Gothic architecture adopting the flying buttresses.If you come up with a solution you won’t know how well it works until you’ve built it and given it the test of time.