This chapter describes the requirements that affect the design of the building envelope for residential buildings. The building’s design and choices made for individual components can significantly impact the energy demand needed to meet heating and cooling loads to maintain the building’s desired inside comfort temperature. 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 and skylights.