If a pre-existing building does not provide sufficient off-street parking, the building may be remodeled or rehabilitated (but not enlarged) without providing additional parking if the existing use within the building remains unchanged or is changed to a use with the same or lesser parking demand. If the use is changed or enlarged, any additional parking required must be provided. The requirements of this section shall apply to only to the additional parking demand that would be created by the new use above the existing use.