The impact of the k-value change of fibrous insulation materials (i.e. fiberglass) in a typical wall-roof system due to moisture content levels on the thermal and energy performance of a typical residential building under hot-humid climatic conditions is investigated. Moisture performance is investigated utilizing theoretical long-term hygrothermal performance modeling and simulation techniques. Layer- and time-averaged levels of moisture content in the fibrous insulation are determined and the corresponding k-value change is evaluated from measured relationships. The impact of the k-value change due to moisture on the building thermal load and cooling energy performance of a residential building is then assessed utilizing detailed building energy simulation software. Limited change in the building cooling energy occurs as a result of the insulation k-value change due to moisture content occurring under moderate wetting conditions. When higher wetting conditions prevail the effect of k-value change on the building cooling energy continues to be limited although the impact of the roof on monthly cooling load is more pronounced especially during the summer months when as much as an 8% increase occurs. In general, the overall building energy performance is less affected by the k-value change of the moist fiberglass insulation under hot-humid conditions. (C) 2013 Elsevier B.V. All rights reserved.