There is provided a building formwork module (12) for use in a modular formwork system (10). The module (12) comprises a first face (14) and a second face (16) that are connected by a web (20). The faces (14,16) and web (2) define two channels (22, 24) that extend along the longitudinal length of the module (12). The channels (22, 24) are able to accommodate wall forming material such that the wall forming material is able to solidify therein. The web (12) in the module (14) provides the module (12) with a rigidity that maintains a relatively flat outer surface on at least the first side (14) of the module (12) against what would be the pressure applied by wall forming material as it solidifies within the two channels (22, 24).