The Eurocode for DIN EN 1991‑1‑4:2010‑12 describes wind loads acting on structural systems. The document also contains a wind load scheme specified for flat and duopitch roofs in particular. The set of rules considers a pitched roof with a roof pitch of less than 5 degrees as a flat roof.
In practice, however, the analysis model of flat roofs is not always defined as absolutely horizontal, often for structural reasons, but with a duopitch roof inclination of less than 5 degrees. This non-planar buckled roof shape is then loaded according to the loading rules for flat roofs.
For applying wind loads to roofs, the RFEM 5 or RSTAB 8 analysis program provides a generator for pitched gable roof shapes and planar flat roof shapes. The special case of a gently pitched duopitch roof shape smaller than 5 degrees is recognized by the load generator of duopitch roof shapes. In this situation, the generator applies a load specification for an equivalent flat roof.