The article analyses rationale for section 2 of article 555 of the Civil Code of the Russian Federation, which states that the price of a building by default includes the price of the land beneath it. Based on the results of a price survey, the author argues that built-up areas are not circulable and do not have any individual market value. The author suggests that land which has not been assigned any individual price is excluded from the market since it is considered to form a single object of ownership with a building on it. The author concludes that the principle of ownership unity presents section 2 of Article 555 in a new light, proving that it is not merely a technical provision, but a clear evidence of an unbreakable legal bond between a building and the land beneath it. In addition the author examines the question of cadastral costs of a build-up land and discusses possibilities of its application.