Which type of insulation should not be installed around knob-and-tube wiring?

The correct answer indicates that no form of insulation should be installed around knob-and-tube wiring. This is because knob-and-tube wiring systems were designed to operate without insulation covering them, allowing for air circulation around the wires, which helps to dissipate heat. If insulation is placed too close to or directly around knob-and-tube wiring, it can create a hazardous situation by increasing the risk of overheating and potential electrical fires.

Knob-and-tube wiring itself dates back to the early 20th century and has certain limitations and safety considerations that modern insulation materials do not accommodate. Any form of insulation—be it loose, rolled, or foam-in-place—could trap heat generated by the current flowing through the wires, leading to dangerous conditions. Therefore, regulations and safety codes typically prohibit insulating materials from being installed around this type of wiring.

By recognizing these factors, it's critical for home inspectors and those working with older electrical systems to be aware of the risks associated with insulating around knob-and-tube wiring and to recommend safe practices in these environments.