Knob and tube wiring is an older type of electrical wiring that's no longer used and generally not considered safe. However, some homes still have it, or may have a knob and tube wiring system that was incorrectly modified or rigged to work with a modern electrical system. Knob and tube wiring may contain asbestos insulation, but the only way to know is to have the material professionally tested.

Asbestos was most commonly produced and integrated into building products from the 1920s to the late 1980s. In reality, asbestos use should have ceased much sooner because asbestos was linked to cancer in studies produced as early as the 1950s. You can even extend that number past the 1980s due to stockpiled materials and because some countries treat asbestos use differently. It may also be found more in commercial applications than residential.

When asbestos fibers become airborne, they enter a person's respiratory system. These fibers scar and damage the lungs and often lead to serious cancers like mesothelioma. Like many dangers in the house, asbestos isn’t easy to see when it could be causing serious damage. The amount of time exposed, combined with the person’s tolerance for asbestos inhalation and the amount inhaled, will all contribute to health problems.

Asbestos itself does not typically leak from a roof. However, if an asbestos-containing roof is damaged or deteriorated, it can release asbestos fibers into the air. This can occur when the roof is disturbed, such as during maintenance or repairs, or due to weathering over time. Exposure to airborne asbestos fibers can be harmful to health, so it is important to address any damaged asbestos roofs promptly and safely.