Siding is the outer covering or cladding of a building's exterior walls. Siding is typically installed to protect the structure from the elements such as rain, snow, wind, and sunlight, while also enhancing the aesthetic appeal of the building.

metal siding and roofing and are applied vertically (up and down) to either 4x8 sheets (plywood or OSB) or to horizontal boards called girts.  Metal panels used as siding can be cut to different lengths and run the entire length of the wall in many cases.  These panels are typically screwed into sheathing or girts to be attached to the building. The metal panel screws have a synthetic collar to create a water-tight bond.  Non-metal siding is usually nailed to sheathing with a 12" to 16" spacing of the nails.