System for covering flat surfaces able to be installed on support structures formed from support poles (2) kept in position by a network of tie rods (3), both the support poles and the tie rods being fixed onto the surface through suitable pins. Said system comprises elongated support elements positioned between such poles (2) that support protection nets or protection sheets (7) that in open position cover the area beneath the support structure and that in closed position are positioned compacted and amassed between adjacent poles of the same row, the movement for passing from the open position to the closed position and vice-versa taking place by sliding of the sheet along the support elements through moving means.
