Our competition entry for the headquarters and research building of a large corporation in Finland exploited the ideas first postulated by Pier Luigi Nervi at the Gatti Wool factory in 1953. Lines of principle stress are joined to form ribs in the soffit of a reinforced concrete flat slab. The volume of concrete is reduced in comparison to a ‘conventional’ reinforced concrete slab, reducing emboddied carbon and enhancing the thermal mass characteristics. The exposed lines of structure are an expression of the reaction of the frame to external load. We have written our own software to model the stress vector field and resulting downstand ribs.