The masonry envelope over a steel structure in a 10-story building failed and had to be replaced after 17 years of service because of severe deterioration of some materials within the masonry walls. The building was designed for use as an office block but it was used for display, servicing, and storage of art treasures for which the inside atmosphere was maintained at a temperature of 21 degrees C and 50% relative humidity the year round. The highly humidified air, in escaping through leakage paths in the building envelope, lost moisture by condensation which accumulated in and on the building materials. This led to the degradation of mortar, deterioration of masonry by frost action, and corrosion of metal ties and fasteners.