How to Replace Knob and Tube Wiring Without Tearing Down Walls

Overview of Knob and Tube Wiring

Knob and tube wiring was commonly installed in homes built before 1950. It consists of individual wires that are run through the wall cavities and held in place with ceramic knobs. The wires are not bundled together like modern electrical cables, and they lack a ground wire.

While knob and tube wiring was suitable for the electrical needs of the time, it does not meet today's safety standards and cannot handle the increased power demands of modern appliances and electronics. Replacing knob and tube wiring usually requires tearing open walls to access and remove the old wiring. However, there are some methods that allow you to replace knob and tube wiring without major demolition.

Preparation

Before beginning any electrical project, make sure to turn off the power at the main breaker panel. Verify power is off by testing outlets with a non-contact voltage tester. Have a qualified electrician inspect your existing knob and tube wiring to determine if any parts can be reused safely. They may also be able to provide advice on the best approach for your specific situation.

Assemble all necessary materials - new NM electrical wire, wire staples, wire nuts, junction boxes, conduit, and tools like a fish tape. Check local building codes for any requirements regarding replacement wiring methods. Inform your insurance company of the project if your policy requires it.

Running New Wiring Through Walls

One method is to run the new wiring through the existing wall cavities without removing any drywall. This takes some finesse and patience but avoids major demolition:

• Carefully probe inside the walls with a long drill bit to create a pathway for the new wiring between access points like outlets or switch boxes.

• Use a fish tape to pull the new cable through the pathway. Secure with wire staples.

• Connect the new wiring to existing outlets and switches. The junction boxes will remain concealed inside the walls.

• Label the new wiring at all access points to distinguish it from the old. The old wiring must be removed eventually.

This works best for straight vertical and horizontal runs. It may be challenging for complex circuit routes or accessing awkward areas. The amount of new wiring run this way is also limited by the filled wall cavities.

Fishing Wiring Down Interior Walls

For upper floor rooms, one option is dropping the replacement wiring down through interior wall cavities from the attic above:

• Drill access holes in strategic areas of the ceiling, trying to line up with interior wall stud cavities.

• From the attic, feed the new wiring down through the wall stud cavities until reaching the access holes.

• Pull the cables the rest of the way into the room and connect to outlets and switches.

This avoids exterior walls or complex horizontal runs. But it still requires drilling holes in the ceiling and patching afterwards. Carefully dodging plumbing vent stacks and other obstructions in the walls is key.

Surface-Mounted Wiring

If the walls have adequate concealment, it may be possible to run some or all of the new wiring externally through conduit or plastic raceways:

• Secure conduit or raceways in out-of-the-way areas like along floorboards, the underside of stairs, or in closets.

• Paint them the same color as the walls for camouflage.

• Use surface-mounted junction boxes to transition from surface to concealed wiring.

This allows access to wiring without demolishing walls, but it results in visible surface wiring. It works best in unfinished basements or attics.

Summary

While challenging, knob and tube wiring can often be replaced without opening up walls in a major way. This requires careful planning, strategic access points, and a degree of luck in navigating existing obstructions. A qualified electrician can determine if any of the old wiring can remain, guide you through the most efficient approach, ensure code compliance, and provide a safe installation.