That which you rent space within a self-supporting structure. Another example may be clearer: The walls are necessary for the building itself to stand and surv

That which you rent space within a self-supporting structure. Another example may be clearer: The walls are necessary for the building itself to stand and survive the winter, but the paint or wallpaper are not. They're only necessary for the tenant, the house would stand securely without any wallpaper. You obviously want cupboards and a kitchen bench, but they don't matter for the building or the safety of the other tenants.