This document specifies requirements on durability, reliability and safety of small and large custom built solar heating and cooling systems with liquid heat transfer medium in the collector loop for residential buildings and similar applications. This document also contains requirements on the design process of large custom built systems. This document (EN 12977-1:2012) has been prepared by Technical Committee CEN/TC 312 "Thermal solar systems and components", the secretariat of which is held by ELOT, Greece. This document is currently submitted to the Unique Acceptance Procedure. This document replaces CEN/TS 12977-1:2010.