Measurements have been made of the air-leakage rates through structural components of conventional metal-panel and concrete buildings which may serve as containment for nuclear reactors. The component measurements included structural penetrations such as doors and louvers as well as materials such as caulking compounds, gaskets, and paints. Specimens were sealed inside of test vessels. Pressure differentials were generated across the specime:q with each component installed in the manner of typical construction techniques. From measurements of the pressure difference as a function of time, the volumetric leak rates were computed. After the major leak paths were determiped, additional tests were made with improved methods of construction. A detailed description and the results of every completed test are presented .