sheathing

In by Mark Goodman

The boards or sheet material fastened to the roof rafters on which the shingles or other roof covering is laid.

Merriam-Webster Online Dictionary
sheathing (noun)
1.
the action of one that something - sheathes
2.
material used to something - sheathe , especially the first covering of boards or of waterproof material on the outside wall of a frame house or on a timber roof
sheathing (Wikipedia)
Highly decorative wood-shingle siding on a house in Clatskanie, Oregon, U.S.A.

Siding or wall cladding is the protective material attached to the exterior side of a wall of a house or other building. Along with the roof, it forms the first line of defense against the elements, most importantly sun, rain/snow, heat and cold, thus creating a stable, more comfortable environment on the interior side. The siding material and style also can enhance or detract from the building's beauty. There is a wide and expanding variety of materials to side with, both natural and artificial, each with its own benefits and drawbacks. Masonry walls as such do not require siding, but any wall can be sided. Walls that are internally framed, whether with wood, or steel I-beams, however, must always be sided.

Most siding consists of pieces of weather-resistant material that are smaller than the wall they cover, to allow for expansion and contraction of the materials due to moisture and temperature changes. There are various styles of joining the pieces, from board and batton, where the butt joints between panels is covered with a thin strip (usually 1 to 2 inches wide) of wood, to a variety of clapboard, also called lap siding, in which planks are laid horizontally across the wall starting from the bottom, and building up, the board below overlapped by the board above it. These techniques of joinery are designed to prevent water from entering the walls. Siding that does not consist of pieces joined together would include stucco, which is widely used in the Southwest. It is a plaster-like siding and is applied over a lattice, just like plaster. However, because of the lack of joints, it eventually cracks and is susceptible to water damage. Rainscreen construction is used to improve siding's ability to keep walls dry.

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