A method for manufacture of a fire-proof and insulating prefabricated building wall, comprising the steps of positioning an interior load-bearing reinforcement structure with a number of reinforcing members (2a, 2b) into an expansion mould with a mould wall comprising interior mould surfaces enclosing a plate shaped volume, blowing beads of an insulating expandable plastic material into the expansion mould, expanding the beads in the expansion mould and allowing them to melt together to form a foamed core plate of a plate shape corresponding to the plate shape of said plate shaped volume, said plate shape of the core plate comprising plate surfaces including two major plate surfaces (10, 11), the beads ultimately expanding to encase the reinforcement structure so that the reinforcement structure extends through and is embedded within the core plate with substantially all surfaces of the reinforcement structure that are positioned within said plate surfaces of the core plate being in contact with the core plate, the reinforcement structure and the foamed core plate thereby together forming a load-bearing, insulating wall core, which assumes the general plate shape of the core plate, positioning of the wall core in a formwork mould with a mould wall encasing the wall core, the mould wall comprising interior mould surfaces forming a plate shaped volume, at least one of the major surfaces (10, 11) of the wall core being positioned at a distance from the mould wall, injecting a fire-proof cementitious material into the formwork mould and allowing it to extend at least between the mould wall and said one major surface (10, 11) of the wall core, and allowing the cementitious material to at least partly cure, the cementitious material adhering to said one major surface (10, 11) to thereby provide coating of the one said major surface (10, 11) of the wall core with the cementitious material to form a coating having an outer surface forming a first major surface of the building wall. positioning an interior load-bearing reinforcement structure with a number of reinforcing members (2a, 2b) into an expansion mould with a mould wall comprising interior mould surfaces enclosing a plate shaped volume, blowing beads of an insulating expandable plastic material into the expansion mould, expanding the beads in the expansion mould and allowing them to melt together to form a foamed core plate of a plate shape corresponding to the plate shape of said plate shaped volume, said plate shape of the core plate comprising plate surfaces including two major plate surfaces (10, 11), the beads ultimately expanding to encase the reinforcement structure so that the reinforcement structure extends through and is embedded within the core plate with substantially all surfaces of the reinforcement structure that are positioned within said plate surfaces of the core plate being in contact with the core plate, the reinforcement structure and the foamed core plate thereby together forming a load-bearing, insulating wall core, which assumes the general plate shape of the core plate, positioning of the wall core in a formwork mould with a mould wall encasing the wall core, the mould wall comprising interior mould surfaces forming a plate shaped volume, at least one of the major surfaces (10, 11) of the wall core being positioned at a distance from the mould wall, injecting a fire-proof cementitious material into the formwork mould and allowing it to extend at least between the mould wall and said one major surface (10, 11) of the wall core, and allowing the cementitious material to at least partly cure, the cementitious material adhering to said one major surface (10, 11) to thereby provide coating of the one said major surface (10, 11) of the wall core with the cementitious material to form a coating having an outer surface forming a first major surface of the building wall.