A modular building comprising: a foundation floor having secured therein a plurality of anchor elements; a plurality of wall-retaining track elements adapted to engage wall panels of the building, the track elements being securable to the foundation floor so as to define the position of at least the load bearing walls of the building; wall panels locatable with respect to the track elements, each panel including at least one channel or duct formed therein parallel to a longitudinal axis thereof and at least one channel or duct formed therein disposed perpendicularly to and laterally of the longitudinal axis; and a plurality of securing members adapted to pass through and locatable within said channels or ducts, the securing members being anchored at each end thereof so as to maintain the panels in fixed relationship to one another.