One of the requirements in the construction of suspended timber floors is that of providing grooves or slots in the joists to take the various services without weakening the joists. The greatest danger of decay in a new building undoubtedly arises in the first 12 months after completion, due to the presence in the brickwork, plaster and concrete of the 'moisture of construction'. When the floor itself forms a decorative feature it is usually constructed from hardwood and secretly nailed. The construction of upper floors differs from that of ground floors in that the floor as well as a ceiling has to be carried without intermediate support for the full span of the room. The varied forms of stair plans often require a landing which is L-shaped and involves some type of cantilever construction. Indeed if the building is soundly constructed with clean cavities in the walls, little trouble need be anticipated in this direction.