What Is Knob and Tube Wiring?
Knob and tube is an early electrical wiring method used in homes built roughly up until 1950, identifiable by individual insulated wires running through ceramic knobs (for support) and tubes (where wires pass through framing members), rather than the bundled cable used in modern wiring.
Why It's a Concern
Knob and tube wiring itself isn't inherently unsafe when installed and maintained correctly, but it lacks a ground wire, which modern electrical devices and outlets are designed to use. It's also frequently found with decades of amateur modifications, and — a significant concern — the original rubber-based wire insulation becomes brittle and can crack with age, especially if the wiring has ever been covered with insulation, which knob and tube was never designed to have contact with.
What We Look For
- Visible knob and tube wiring, typically in an unfinished attic or basement
- Condition of the wire insulation where accessible
- Whether the wiring has been covered by insulation, which is a fire risk
- Evidence of amateur splices, extensions, or modifications over the years
What this means for you
Many insurance providers in BC will not insure a home with active knob and tube wiring without an inspection, and some decline coverage or require it be replaced entirely. This is worth confirming with your insurance provider before removing subjects on a purchase.
What to Do If You Find It
Full rewiring by a licensed electrician is the standard recommendation, particularly if the home will be insured, renovated, or if any wiring is covered by insulation. Partial remediation is possible in some cases, but a licensed electrician should assess the full scope before any work begins.