A greenhouse (1) has a roof (2) including a plurality of substantially parallel crossbeams (3, 3'), at least two longitudinal sections (4, 5, 24, 5') which are mounted to the crossbeams (3) and extend at a distance from each other in transverse direction of the crossbeams (3), a transparent foil (6) which is mounted to the longitudinal sections (4, 5, 24, 5') at respective foil attachment locations (7) thereof so as to form a cover between the longitudinal sections (4, 5, 24, 5'). The roof (2) also includes a displacement mechanism (8, 8') for displacing one of the longitudinal sections (5, 5') with respect to the other (4, 24) between a non-foil-stretching position and a foil-stretching position. The distance between the respective foil attachment locations (7) is larger in the foil-stretching position than in the non-foil-stretching position. The displacement mechanism (8, 8') can be operated and is lockable at an upper side of the roof (2) .
