Today, complex, three-dimensional (3-D), transient thermal performance of building systems can be investigated using either experimental or numerical modeling approaches with a high degree of confidence. The thermal performance of building envelopes without effects of moisture is understood for some envelope systems, and relevant information exists in various handbooks such as the ASHRAE handbook and ASTM manuals. A large body of scientific work is also available in research papers by Kosny et al. [1], Christian et al. [2], Petrie et al. [3], and others.