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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.

There are products that still contain asbestos, but they were typically installed decades ago. Common places where you may still find asbestos-containing materials are in siding, wrapped around ductwork, in older appliances (i.e., stove and gravity furnaces), and in floors. Asbestos was primarily used as an insulator, so anywhere in an older home where you lose heat is where you will most likely find asbestos.

Depending on the size of your home, the inspection process could take a few hours or a few days. While inspecting your home, the asbestos specialist will take small sections of the potentially contaminated material. They will then send the sample to an accredited laboratory or the local health department for testing. 

The cost of asbestos testing depends on your location, the home's size, and the testing area's complexity. Plan to spend between $230 and $800 for testing. During testing and while handling potential asbestos, the specialist may wear protective gear, including gloves, overalls, appropriate footwear, and respiratory equipment.

Unlike some home problems, such as water damage or pest infestations, asbestos can be very difficult to spot. Asbestos is a mineral in the form of microscopic fibers and was previously used in building materials for its bonding and fireproofing abilities. Insulation, roof shingles, ceiling tiles, floor tiles, pipe wrappings, soundproofing materials, and textured paint features like popcorn ceilings are common sources of asbestos, particularly in homes built before 1980.

Age is perhaps the biggest indicator of asbestos, as legislation passed in the 1970s labeled asbestos as dangerous and regulated its use in building materials. Signs of age in the form of wear and tear or material degradation are also indicators that asbestos fibers may be leaking into the air, but ultimately, it’s difficult to detect with the naked eye. If you have reason to suspect asbestos in your home, it’s best to hire a certified asbestos inspector.