The base amount of any owner-occupied single-family dwelling may be further increased above the limitations provided by section of this Act, if there is a change in the use or classification of the property, or to account for any addition to, or expansion of, the property. An addition to, or expansion of, the property may only result in an increase in the assessed value above the limitations provided by section of this Act by the difference in assessed value between the real property with the addition or expansion and the real property as if no addition or expansion was made. For purposes of this section, the increase in taxable value from improvements to an owner-occupied single-family dwelling does not include additions to, or improvements of, existing structures affixed to the land if the improvements result in an increased assessed value of forty percent or less of the current assessed value. 25