Knob and Tube and Aluminum Wiring: Repair, Replace or Rewire?

Knob and tube wiring

Used into the 1940s, knob and tube runs single wires through ceramic knobs and tubes in the framing. You can often see it in an unfinished basement or attic. It has no ground wire, and its insulation is rubber and cloth that turns brittle with age.

Undisturbed and lightly loaded, it served for decades. The trouble comes from what happened afterward: insulation blown over wires that were meant to cool in open air, modern loads on circuits sized for a few lamps and splices added by several generations of owners.

Aluminum branch wiring

From the mid 1960s to the mid 1970s, some homes were wired with aluminum on ordinary 15 and 20 amp circuits. Aluminum expands and contracts more than copper and forms an oxide that resists current. Over time, connections at outlets and switches loosen and overheat. Warm cover plates, flickering lights and a smell of hot plastic are warning signs.

Aluminum on large circuits, such as the service entrance or a range feed, is normal and still used today. The concern is the small branch circuits.

Your options

For aluminum: every connection can be repaired with connectors approved for joining aluminum to copper, or the circuits can be replaced with copper. Repair costs less and is recognized as a permanent fix when done at every device, splice and fixture.

For knob and tube: replacement is the long-term answer. It can be done in stages, starting with the circuits that carry the most load: kitchen, bath and laundry.

Why insurers and lenders ask

Many insurance companies will not write or renew a policy on a home with active knob and tube, and some ask for documentation on aluminum wiring. An electrical inspection report from an electrician is the usual first step.

What a rewire is like

Most whole house rewiring is done by fishing new cable through attics, basements and wall cavities, with small access openings where needed. Families usually stay in the home. A new panel is often part of the job. See electrical panel upgrade.

Thinking of buying an older home? Read our electrical checklist for home buyers first.