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.

Siding materials can vary widely and may include options such as vinyl, wood, metal, fiber cement, stucco, brick, stone, and synthetic materials like engineered wood or composite panels. The choice of siding material often depends on factors such as durability, cost, maintenance requirements, climate conditions, and architectural style preferences. Most siding materials dictate that the siding runs horizontally (left to right).  Horizontal siding includes vinyl and wood (e.g., cedar) which are the two most commonly seen.  Metal panels are growing in popularity for both 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.