Rene Suarez writes:
I'm building a cob oven in a temperate climate, and I'm trying to avoid unnecessary work. My resources suggest digging/laying the foundation below the frost line. That would be 4 feet deep here. Is this really necessary for a 4x4 oven?
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For those who are just joining us, in temperate climates the winter cold will penetrate into the ground, freezing the water in the soil. That wouldn't be such a big deal except the little oddity of water that when it freezes it expands. Its a very small amount of expansion, but "frost heave" is a very power force. It can push soil and cement pads and houses out of their place by up to a few inches. Since it does so unevenly along the length of say a 40' house, it can break your foundation or cause your house to settle out of level. To keep this from happening we can dig down below the deepest depth frost is expected to penetrate (the "frost line", which in my area of Ohio is about 48" down) and back fill with gravel or concrete so the water drains away and the house doesn't shift. That would be a lot of work to go to for a pizza oven.
Fortunately the ground around a structure as small 4'x4' tend to freeze and thaw pretty evenly, and it isn't essential that a pizza oven stay perfectly level like your kitchen counter, so it will ride out the "heaves" with little chance of damage even if your gravel footer was only a foot deep or so. This is called a "floating foundation". If your soil is reasonably well-drained and certain precautions are taken a floating foundation will even work on larger buildings like Rob Roy's two story cordwood house in upper New York State.
The best book on pizza ovens start to finish is my friend Kiko Denzer's book.
