This chapter describes the requirements that affect the design of the building envelope for low-rise residential buildings. The design and choices made for individual components for the building can significantly affect the energy demand needed to meet heating and cooling loads to maintain the desired inside comfort temperature of the building. Heating and cooling load calculations are used to determine the mechanical system design needed for space heating and cooling. The principal components of heating loads are infiltration and conduction losses through building envelope components, including walls, roofs, floors, slabs, windows, and doors. Cooling loads, on the other hand, are dominated by solar gains through windows, skylights, and roof/attic assemblies.