Cloth Wiring

Introduction: The Three Types of Cloth Wiring We Report On

There are many variations of cloth-insulated wiring, but for inspection and insurance purposes, we group them into three primary types. Each type carries a different level of concern depending on age, material, and safety characteristics.

1. Knob and Tube (High Concern)

Installed from the early 1900s through the 1950s, knob and tube consists of rubber-insulated wires covered with cloth and supported by ceramic knobs and tubes. This wiring is reported in both home inspections and 4-point reports as a high concern, even if no visible defects are present.

2. Rubber-Insulated Cloth Wiring (Moderate Concern)

Used from the 1930s to the 1970s, this wiring features rubber insulation wrapped with a cloth outer jacket. It is reported as a moderate concern on home inspections and 4-point reports due to age, insulation deterioration, and insurance limitations.

3. Thermoplastic-Insulated Cloth Wiring (Informational Only)

Found from the late 1950s into the 1970s, this type uses early thermoplastic insulation with an outer cloth wrap. It is generally considered safe when in good condition. We list it on home inspections as informational only and do not report it as a concern on 4-point reports.

Mixed Wiring in Older Homes

Many older homes—especially those remodeled over multiple decades—contain a blend of these wiring types. Each type is evaluated independently during the inspection, and its classification determines how it is reported to homeowners, insurance ca

1. Knob and Tube (K&T) Wiring – High Concern

Knob and tube wiring is the oldest and most concerning type of cloth-insulated wiring still found in homes. It was widely used from the early 1900s until the late 1940s, with some installations extending into the early 1950s.

How to Identify Knob and Tube

• Ceramic knobs and tubes attached to framing
• Hot and neutral wires run separately
• No grounding conductor
• Rubber insulation covered with cloth sheathing

Why It’s a High Concern

• Brittle, deteriorated insulation
• Cloth attracts rodents
• Exposed conductors increase fire and shock risk
• Often uninsurable or restricted by insurance carriers

How We Report It

• Home Inspection: High concern
• 4-Point Inspection: High concern regardless of defects

Recommended Action

• Evaluation by a licensed electrician
• Plan for rewiring older circuits
• Understand that continued use is not a code violation but not recommended

2. Rubber-Insulated Cloth Wiring – Moderate Concern

Used from the 1930s to the 1970s, rubber-insulated cloth wiring is the second-highest concern because its insulation becomes brittle over time.

How to Identify Rubber-Insulated Cloth Wiring

• Rubber insulation with cloth outer jacket
• Frayed or fuzzy cloth wrap
• Deterioration visible in attics, crawlspaces, or around light fixtures

Why It’s a Moderate Concern

• Rubber becomes brittle or cracked with age
• Cloth jacket can retain moisture or be damaged by rodents
• May affect insurability depending on the carrier

How We Report It

• Home Inspection: Moderate concern
• 4-Point Inspection: Moderate concern regardless of visible defects

Recommended Action

• Have a licensed electrician evaluate active cloth circuits
• Replace deteriorated or heat-damaged sections
• Consider upgrading to modern NM-B wiring during renovations

3. Thermoplastic-Insulated Cloth Wiring – Informational Only

Thermoplastic-insulated cloth wiring, used from the late 1950s through the 1970s, was one of the earliest forms of plastic-coated wiring. It has a thermoplastic inner insulation with a thin cloth outer wrap.

How to Identify Thermoplastic Cloth Wiring

• Plastic inner insulation similar to early NM cable
• Thin cloth wrap around the jacket
• Often includes a ground wire depending on age
• Labeled as early versions of NM cable

Why It’s Not Considered a Concern

• Thermoplastic insulation is stable and safer than rubber-based wiring
• Cloth outer wrap does not affect electrical performance
• Typically not classified as "cloth wiring" by insurers
• Generally acceptable for continued use when in good condition

How We Report It

• Home Inspection: Reported as informational only
• 4-Point Inspection: Not reported as a concern unless damaged

Recommended Action

• No immediate action required when wiring is in good condition
• Replace only if overheating, damage, or improper modifications are found
• AFCI/GFCI upgrades recommended for added protection

Final Message to Consider

While many older homes have operated with cloth wiring for decades without noticeable issues, the concerns surrounding cloth wiring should not go ignored. A building material may appear functional or may be hidden behind finishes at the time of inspection, but once a new homeowner moves in, the dynamics of the home can change.

Electrical demand can increase with new appliances, added electronics, or lifestyle differences. In addition, any remodel—past or future—can directly affect the performance of cloth wiring. If wires are moved, spliced with modern materials, or left abandoned during renovations, the risk of failure increases significantly. In many cases, the rubber insulation found on older wiring can crumble simply from being touched or shifted, exposing the conductor underneath.

If the integrity of the wire has weakened over time, electrical current can generate heat—either rapidly or slowly—which may result in a fire or shock hazard. Because of this, we cannot state with 100% certainty that cloth wiring in a home is completely safe or free of immediate risk. Our role is to document what we can observe and to advise clients when building materials may pose a concern.

We hope this information helps you make an informed and confident decision about your home purchase. If you have any questions or need further clarification, please feel free to reach out anytime.