This thesis introduces a new adjustment factor for the probability-based load and resistance factor (LRFD) design for wood structures. By investigating the empirical data of reaction forces for a wooden house built by the Forest Product Laboratory in 2001, it is found that the reaction values exhibit great variability. To explore the causes of this variability, a 3-D finite element model is built and analyzed using commercial software MSC/Nastran. It is found that differences in member geometry are a major cause of reaction variability. In examining the potential effect the reaction variability might have on the structural safety, reliability is assessed for two different types of wood products under several different situations. Finally, a new adjustment factor Ks, which accounts for the variability in load path, is obtained and validated based on structural reliability theory.