Tunnel formworks are used in building structures which are both from walls and slabs. They are designed somehow in which half of each slab with it adjoining wall and two integrated formworks become mantled as an L-shape all at the same time. After reinforcement, concrete is poured. The location of mechanical and electrical installations can be anticipated in this system and the formworks get opened and closed uninterruptedly. Mantling by crane is done in a minimum time.