Facts
C. (the plaintiff) had a commercial building constructed on his property in X. in 1987/88. Engineering firm A. AG (defendant 1) performed the engineering work and architectural and planning firm B. AG (defendant 2) was commissioned for the architectural work. Architect D. acted as an advisor to the plaintiff. Initially, a steel construction was planned for the new building. However, the plaintiff later decided to opt for a masonry construction and a flat foundation. Shortly thereafter, cracks appeared in the facades, which then widened and multiplied. After unsuccessful negotiations, the parties jointly commissioned building engineer E. to prepare an expert report to determine the causes of the cracking damage, the type of repair, and the repair costs. On October 31, 1990, E. submitted his expert report, with which the defendants did not agree. By an action filed on March 11, 1992 and subsequently amended, the plaintiff requested the Commercial Court of the Canton of St. Gallen to order the defendants to pay him jointly and severally 1,868,600 Swiss francs plus interest at 5% from March 11, 1992.Considerations
The Court first considered that the defendants were not in default in the performance of their contractual obligations, but that it was a case of defective performance, resulting in consequences in terms of damages and not late payment. Consequently, the conditions for the granting of default interest were not met.
However, the Court held that when the damage is calculated at the time of the judgment rendered in the final cantonal instance, the plaintiff is entitled to compensatory interest on the amounts corresponding to the expenses incurred or the loss of revenue suffered prior to the judgment, due to…