Structure vs. Foundation

Out of sight, out of mind. This phrase applies well to the foundation and structure of our homes. It can be a big unknown and confusing area for most of us who are outside the trades. All this makes them even easier to ignore. Until there’s a problem, that is.
Today’s topic is trying to make sense of what is down there on the most elementary level possible. Or, put more simply, what part is my foundation, and what part is the structure?
While this easy rule of thumb does not apply 100% of the time, it will steer you right most of the time:
Your foundation is the concretey stuff under your house. All the bricks, cinder blocks, and concrete are your foundation. In really old homes, some foundations are stacks of rocks.
Your structure is all the wooden stuff under the house, in the walls, and the roof. Anything made with wood is the structure of the home. This includes engineered wood products like an I-joist or a web truss.
There are, of course, countless exceptions to this. The building code allows for and has conditions for wooden foundations. Some houses, usually near water, are built on wooden piers driven deep into the ground. Sometimes, when we repair a foundation, part of the foundation becomes metal. It’s not common in homes, but sometimes steel is part of the structure as well. When a home has a slab foundation, some parts of the slab will only support the floor, which is more structure than the foundation.
But, if you look at your house and say the wood parts are my structure. The concrete, brick, and block parts are my foundation. You will generally be right on the money.