Walls typically represent the largest exterior surface area of a home. As a result, from an energy stand point, the wall system is a major component of the building envelope, particularly in extreme cold climates. When it comes to improving thermal performance, there are many ways to construct a wall, and the details of sealing, sheathing and insulating are even more numerous. At the Cold Climate Housing Research Center, various wall types and building techniques are being evaluated on an ongoing basis. There are many factors that must be taken into account when designing or choosing a wall system: Energy efficiency, cost, resistance to the elements, availability of materials, and the climate in which the wall is expected to perform, are all important considerations.