Host Jeff Wilson explains that exterior walls comprise what is known as the building envelope. This defines the exterior structure of your home.
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Exterior walls are responsible for keeping the comfortable air in and the elements out. All building codes require that you insulate the exterior walls of your home. This is done in-between the wood studs of the frame. Here's a look at some energy-efficiency factors to consider for walls:
Note: Sometimes sheathing can be foam insulation — or rigid board. There's no structural loss using rigid board, and it's basically a better insulator for your home.
Other air infiltration barriers are polyurethane sheets that protect the house from moisture. The siding of the house is then applied on top of the air infiltration barrier. This can be a good wood paneling, a wire or a stucco surface.