The invention relates to a truss (1) for forming a light construction building, said truss (1) comprising vertical posts (2,3,4) arranged in at least two base rows (L1,L2), and a couple roof (8) formed by rafters (6), binding beams (6a), purlins (7a) and a purlin ridge (7) is fixed to the vertical posts (2,3,4)； and a bracing member arranged between at least two, first and second adjacent vertical posts (3,4) is connected said posts (3,4) in each row (L1.L2), and the bracing member is connected to the upper section of the first post (3) at its first end, and the bracing member is connected to the lower section of the second post (4) at its second end, the bracing member is a bracket bar (10) to be loaded equally by compression and tensile forces, wherein a further bracket bar (11) to be loaded equally by compression and tensile forces is arranged between the first vertical post (3) and the adjacent third vertical post (5) in each row (L1.L2), the bracing member (11) is connected to the upper section of the first post (3) at its first end, and the bracing member (11) is connected to the lower section of the third post (5) at its second end； the bracing members (10,11) is connected to the same fixing point (12) in the upper section of the first vertical post (3)； and push bars (13) arranged in planes parallel to the plane (S1,S2) of the couple roof (8) and connected to at least the rafters (6) are attached to the fixing point (12) at their first end, and each push bar (13) is attached to the purlin ridge (7) at their second end； and further push bars (13) are connected to vertical posts (2a, 2b) in the base rows (L1,L2) at their first ends and fixed to the purlin ridge (7) at their second ends； the invention also relates to a heat expansion unit formed by trusses (1 ), and to a light construction building formed by heat expansion units, and a method for improving stability of a light construction building.
