From the structural point of view, a building consists of the following parts:

1. The foundations.

2. The enclosing walls.

3. The columns and bearing partitions.

4. The floors.

5. The roof.

If the building is very narrow, columns and bearing partitions may not be used, but the other four components are always present. Steel enters into the composition of the last four named parts to a greater or less extent in nearly every building, and these steel members are collectively called the framework of the building. Leaving the discussion of the subject of foundations until later, we shall consider briefly the component parts of the other divisions that may be said to constitute the elements of a building.