Abstract: A method and building construction element for manufacturing thermally insulated buildings, in which building construction elements are applied which have the form of half a truss with an outer arch side, an inner arch side and two sides of shape plate truss, comprising a core of synthetic hard foam of which the outer arch side and the inner arch side are provided with plate-like coverings and of which sides are uncovered, which half trusses are combined at the construction site to form complete trusses, arranged in adjacent relationship, whereafter the adjoining surfaces are sealingly interconnected. In the method for manufacturing the building construction elements, a mold of corresponding shape is provided comprising an open side and arranged with the open side up, while the upright bent walls of the mold are provided on the inside with a plate-like lining, whereafter the mold is supplied through the open side with the foaming reaction mixture.