A nuclear shelter, particularly for construction by assembly from a kit of parts, has a load-bearing skeleton structure (13), e.g. of metal tubes (15,16,17) clamped together, which are capable of limited deformation under the pressure wave from blast. This structure is covered by mesh (18) supporting resilient material (14) which in turn is covered by an impermeable membrane (12), e.g. of butyl rubber, surrounding the whole structure. This membrane which forms a gas-tight and water-tight enclosure is covered with earth, sand or the like to give radiation protection.