Friable asbestos is most commonly found in which two building materials?

Friable asbestos is most commonly found in ceiling tiles and sprayed-on insulation because these materials are more likely to crumble, break down, or become airborne when disturbed. Friable asbestos is defined as asbestos-containing materials that can be easily pulverized or reduced to powder by hand pressure, which increases the risk of asbestos fibers being released into the air.

Ceiling tiles were often made with asbestos in the mid-20th century for their fire resistance and insulating properties. Similarly, sprayed-on insulation, commonly used on beams, ceilings, and walls, utilized asbestos for its insulating properties. When these materials are in good condition, they may not pose a significant risk; however, if they are disturbed or deteriorating, they can release harmful asbestos fibers.

The other materials listed, while they can contain asbestos, are typically found in forms that are not classified as friable, meaning they are less likely to release fibers into the air under normal circumstances. For instance, roofing materials and wall panels tend to remain intact unless physically damaged.