Exterior cladding is a protective layer of materials that separates a building's structure and interior from exterior elements, such as weather and sound. The exterior cladding is often not one material but an assembly of materials, and each material has its own importance in blocking exterior conditions. For example, a contemporary house will have an exterior veneer of siding or brick, a moisture resistant plastic wrap, insulation and a vapour barrier to protect the interior.
Water is often considered the hardest element to defend against on a structure. Moisture is repelled using siding, waterproof membranes, weeps, sealant, weatherstripping and flashing. The siding is the first line of defence and is usually the most important and durable cladding element. The membrane, sealant, flashing, etc, protect the structure from any moisture that penetrates the siding.
Exterior cladding protects a structure from temperature extremes and variations by insulating the interior from the exterior. Rigid insulation, built-up layers of material, and double-glazing protect the interior from exterior temperatures by creating thermal gaps that do not allow the temperatures to be conducted through the cladding, bridging exterior temperatures to interior temperatures.
The building's structure and interior are shielded from the wind by the exterior cladding. To avoid damage to the cladding, the materials are redundantly and securely fastened to the structure, while allowing minimal movement by the wind. The method of fastening the cladding to the structure is especially important in areas with hurricanes, tornadoes and heavy thunderstorms, which produce high velocity winds.
Exterior cladding deters damage and deterioration from the sun and ultraviolet waves. A structure's exterior elements must be able to resist the harmful effects of the sun. Otherwise, the failing material will provide access to the interior for moisture and temperature. Many plastic and wood products are not appropriate for exterior cladding because they can degrade quickly when exposed to the sun.
Many contemporary cladding systems are novel and provide protection from the exterior with a thin skin. Modern systems such as aluminium and glass architectural glazing can insulate and shade a building as well as traditional masonry and wood systems. Other cladding systems are similar to screens, able to filter out the wind and sun, but allowing air to flow through the structure's skin.