Abstract: A modular unit (10) for a building comprises a central frame (12) and four walls (14) arranged in opposing pairs on each side of the central frame (12) to give an I-shaped configuration. At least one of the pairs of opposing walls (14) is foldable towards the central frame (12) to make a unit of ?-shaped or!-shaped configuration. The units (10) can be connected in series to make an extended building. The modular unit (10) is fitted with flooring (16) and a roof (22). Seals are provided between the central frame (12) and the walls (14), and between adjoining walls (14) in a multi-unit structure.