Building “Envelope” generally refers to those building
components that enclose conditioned spaces and through
which thermal energy is transferred to or from the outdoor environment. The thermal energy transfer rate is
generally referred to as “heat loss” when we are trying to
maintain an indoor temperature that is greater than the
outdoor temperature. The thermal energy transfer rate is
referred to as “heat gain” when we are trying to maintain
an indoor temperature that is lower than the outdoor
temperature. While many principles to be discussed will
apply to both phenomena, the emphasis of this chapter
will be upon heat loss.