Once the exterior wall and roof framing are in place, the next phase of construction involves applying the home’s skin to strengthen the structure and make it weather-tight. The strength is supplied by installing bracing and sheathing, and the weather-tightness comes from applying layers of insulation and other barriers. It’s important to complete this phase quickly and pay attention to details that protect the framing from moisture and assure the home’s energy efficiency.
In many older homes, the wind literally blew through cracks in the walls. It carried away indoor moisture and pollutants along with heated or cooled air. Energy-efficient homes, by contrast, depend on precise engineering of exterior walls to create a predictable, controlled indoor environment.
Building the wall system best suited to your home will require a marriage of diverse materials—vapor barriers, air barriers, insulation, sheathing, and in some cases, insulating panels. These products work together to control the passage of air, heat and moisture between the inside and outside of your home, while also bracing the frame.

Vapor Barriers
A tight vapor barrier inside exterior walls prevents indoor moisture from moving into stud cavities where it can condense and rot your home from the inside out. Unlike air barriers, which resist the flow of air but allow water vapor to pass, vapor barriers limit the diffusion of water molecules. Builders often use polyethylene (plastic sheeting) as an inexpensive vapor barrier, although other materials including foam, foil and specially formulated paints also can serve as vapor retardants.
Look for these details when polyethylene is installed: All seams in material should overlap. Reinforced tape should cover not only the seams, but any exposed nails or staples. A bead of flexible caulking will create an airtight union between vapor barrier and sole plate at the base of the wall. To keep electrical outlets and other mechanicals from breaking the continuous membrane, the barrier must be carefully cut, adjusted and caulked to fit around awkward intrusions.