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.

Costs depend on the number of samples, property size, and lab processing fees.

If you hire a dedicated asbestos inspector near you in addition to your local home inspector, it will cost between $200 and $800. If, however, your general home inspector happens to be certified as an asbestos inspector, they can charge you a smaller fee and tack on the cost to the home inspection. In general, home inspectors do not do physical testing, but will provide a visual assessment so you know what you are working with.