The degradation of wood changes various properties; these changes can favor its usage in particular instances, e.g., as an insulation material. Knowledge of the moisture content and movement of moisture in building materials is crucial. The primary focus of this paper is the diffusion coefficient and equilibrium moisture content of three wood species after degradation via Trametes versicolor. Values for the diffusion coefficients were determined under different conditions: a temperature of 20 °C ± 2 °C; and 3 relative air-humidity settings, i.e., 30% ± 3%, 60% ± 3%, and 96% ± 3%. The differences in the longitudinal and transversal directions were statistically significant for all conditions, while the differences in the diffusion coefficients were non-significant for the first two relative-air-humidity settings. A portion of the diffusion coefficient calculation data was used to develop a sorption isotherm for all wood species. The equilibrium moisture content of the degraded wood was determined for each condition. Duncan’s multiple-range test showed that the wood species was a significant factor; therefore, the isotherm had to be plotted for each wood species. The number of sorption sites in the monolayer in degraded spruce wood was different from the number in degraded beech and oak wood.