Subject to the provisions of article 15-II, the gross income of buildings or parts of buildings which the owner reserves the right to use is made up of the amount of rent that they could produce if they were let. It is assessed by comparison with similar properties or parts of properties that are let on a normal basis, or, failing this, by direct assessment. It is increased, where applicable, by the revenue referred to in the second paragraph of Article 29. This provision does not apply to hunting rights.