For quite some time, it has been fairly widely known that 15-lb. and 30-lb. asphalt-saturated organic felts do not really weigh 15 and 30 pounds per square, respectively. They weigh somewhat less. In fact, to avoid confusion, the nomenclature of the product changed to “No. 15 asphalt felt” and “No. 30 asphalt felt” sometime in the late 1970s or early 1980s. The conundrum today is: When is No. 30 asphalt felt not No. 30 asphalt felt? This article will explore the history of the weight classification and nomenclature of asphalt-saturated organic felt, examine the labels being placed on felt manufacturers’ products, explain why there is confusion in today’s roofing felt marketplace, and offer suggestions for specifying new felt underlayments. This is all to help ensure that the No. 30 felt you specify and that your clients expect to be installed on their roof decks really does weigh 26 pounds per square. Confused? Read on.
This article was originally published in the November 2019 issue of IIBEC Interface, the official publication of the International Institute of Building Enclosure Consultants.