Siding may be made of wood, metal, plastic (vinyl), masonry, or composite materials. It may be attached directly to the building structure (studs in the case of wood construction), or to an intermediate layer of wood (boards, planks, plywood, oriented strand board) called sheathing (or sheeting). Siding can also be attached with wood strips to masonry walls. An intermediate air/moisture barrier such as house wrap or felt paper may be applied to the sheathing or a modern sheathing material that also serves as an air/moisture barrier such as an insulation board.
Siding may be formed of horizontal or vertical boards, shingles, or sheet materials. In all cases, avoiding wind and rain infiltration through the joints is a major factor, met by overlapping, covering or sealing the joints, or by creating an interlocking joint such as a tongue and groove or a locking channel. Since building materials expand and contract with changing temperature and humidity, it is not practical to make rigid joints between the siding.