How to Safely Retrofit Knob and Tube Wiring in Heritage Homes

What is Knob and Tube Wiring?

Knob and tube (K&T) wiring was an early standardized method of electrical wiring used in buildings in Canada and the United States from about 1880 to the 1940s. It consisted of single insulated copper conductors run within wall or ceiling cavities, passing through joist and stud drill-holes via protective porcelain insulating tubes, and supported along their length on nylon knobs attached to the structural framing.

While K&T wiring provided an improvement in safety over previous exposed wiring methods, it has a number of drawbacks compared to modern electrical wiring:

These safety concerns mean K&T wiring often needs to be replaced in heritage homes, but this can be challenging due to the invasive nature of retrofitting modern wiring in old buildings. Careful planning is required.

Why Retrofit K&T Wiring in Heritage Homes?

There are several compelling reasons to consider retrofitting K&T wiring in heritage buildings:

At the same time, heritage regulations often tightly control the extent to which historical buildings can be modified. Sensitive retrofitting of wiring maintains heritage character while improving safety.

Planning a K&T Wiring Retrofit in a Heritage Home

Careful planning ensures a successful K&T wiring replacement project in a heritage building:

Research Building Plans and Permits

Develop a Retrofit Plan

Consult Heritage Approval Authorities

Secure Electrical Permits

Safe Techniques for Installing New Wiring in Heritage Buildings

Once necessary permits and approvals are in place, K&T wiring replacement work can begin. Some safe installation techniques include:

Prioritize Removal of Risky Branch Circuits

Retain Original Decorative Switch Plates and Outlets

Fish Wires Through Finished Walls

Run Wires Through Attics, Basements and Crawlspaces

Repair Walls and Ceilings with In-Kind Materials


While rewiring old heritage buildings with modern electrical wiring requires care and expertise, it can be done safely. Following heritage regulations, using less-invasive wiring techniques, and repairing surfaces appropriately retains the heritage character while eliminating the considerable risks of deteriorated knob and tube wiring. With careful planning and the right tradespeople, heritage homes can provide safe, comfortable living for years to come.