Because we believe that knowledge shared is knowledge doubled or even tripled, we have formulated 113 questions on the subject of architecture, which we are publishing in our e-paper series. Economic efficiency is one of the most important fundamentals for buildings - only what pays off will ultimately be a "successful" building. This ranges from the construction costs to the costs of ongoing operation - cradle-to-cradle. We deal with cost-effectiveness in a separate e-paper as part of the 113 questions on architecture