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The layers we can actually see on the interior and exterior of a building are called the 'finishes'. The way that these layers look on a building may also be combined with how they can perform as part of the building envelope.

Finish layers on a building may serve a variety of functions:

• Exterior Cladding or Siding: A durable exterior finish may contribute to the overall longevity of a building. Materials such as brick, stone and wood have been used as cladding for centuries. Modern materials such as fibreglass, vinyl and composite woods are highly favoured for new home construction for price and easy installation.
  
• Exterior Trim and Flashing: Elements of trim on building exteriors help to transition around openings, at corners, at the foundation and at the roof. Flashing layers help to direct water away from the building and are usually made of bent pieces of metal or plastic, located around openings, in roof valleys and at bottom edges of exterior finishes.
  

• Roofing: From asphalt and metal, to wood and slate, roof finish materials all serve the same function - to shed rain and snow down and away from the building. Roofing may need replacement over the life of the building, while some materials may only need regular maintenance to maintain integrity.
  
• Interior Trim: While mostly decorative on the inside of a building, interior trim is often used to close gaps around openings and at junctions like floors and ceilings. Trim may be simple and plain, or very ornate, depending on the architectural style and age of a building.
  
• Gypsum Drywall and Plaster: Broad expanses of interior surfaces may be covered with gypsum drywall panels or, in older buildings, plaster coatings. Some applications of these materials may be done to make an airtight layer.