What is knob-and-tube wiring and does it matter?
Pre-1950s wiring with no ground, insulated with cloth and rubber that becomes brittle. It matters mainly because insurers surcharge, condition or decline on it, and a full replacement is a five figure job.
The wire runs through porcelain knobs and tubes and has no ground conductor. Undisturbed and correctly loaded it can still function, which is why it is still in service in parts of Toronto. The failure modes are what concern insurers: brittle insulation, connections made outside junction boxes, and homeowners burying it under blown-in insulation where it overheats.
Practically, the question is not whether it is dangerous today but whether you can insure and finance the house. Many insurers require replacement within a set period or refuse the risk, and a lender will not advance funds on a property you cannot insure.
Get an electrician licensed by the provincial regulator to quote a full rewire including the service upgrade that usually accompanies it. Then decide with that number in hand, during your condition period.
Answer it with your own numbers
You will need: municipality.
Find electricians, with the ESA licence each record listsNext questions
What makes a house hard or expensive to insure?
Knob-and-tube or aluminum wiring, galvanized or polybutylene plumbing, a sixty amp service, a roof past its life, an oil tank, and a history of water claims. Any of these can mean a surcharge, a condition to fix within thirty days, or a refusal.
Ontario
What are the red flags in an older Toronto house?
Knob-and-tube wiring, a sixty amp service, galvanized supply pipes, a clay drain line under mature trees, an underdug basement without proper underpinning, vermiculite insulation, and any unpermitted basement apartment.
City of Toronto