What Is Knob-and-Tube Wiring and Should You Replace It?

August 13, 2026 · Family-owned electricians in North Idaho

CC0, via Wikimedia Commons

If your house still has knob-and-tube wiring, the wiring itself isn't automatically dangerous just because it's old. What matters is its condition, whether it's been modified over the decades, and whether you're about to insulate or remodel around it. In most cases in this region, the honest answer is yes, plan to replace it, but the urgency depends on specifics.

The short answer

Replace knob-and-tube wiring before you add insulation, remodel a space it runs through, or increase the electrical load in the home. Knob-and-tube was designed to dissipate heat into open air. It was never rated for the situation most old North Idaho farmhouses and cabins are in now, which is buried under blown-in attic insulation or wrapped in newer materials during a remodel. That's when the fire risk actually goes up, not just from age.

What changes the timing

A few things push replacement earlier or let it wait a little longer:

• Insurance requirements. Many insurers in Idaho won't write or renew a homeowners policy on a house with active knob-and-tube wiring, or they require an inspection first. This is often the deciding factor, not the wiring's actual condition.
• Insulation plans. If you're planning to add attic or wall insulation, the wiring needs to be dealt with first. Covering knob-and-tube with insulation is a known fire hazard because the wires can't shed heat properly.
• Splices and DIY additions. Original installations from the 1900s through the 1940s were often done competently for their era. The bigger risk is usually decades of amateur additions, tapped-in outlets, and splices hidden in walls or attics.
• How much of the house still uses it. Some homes have knob-and-tube only in an attic or a single addition, with the rest already updated. Partial systems are a smaller, more contained problem than a house running entirely on original wiring.

Signs you are overdue

Some symptoms suggest the wiring needs attention sooner rather than later:

• Warm, hot, or discolored outlet and switch covers
• Frequent tripped breakers or blown fuses, especially on circuits with several outlets
• Visible ceramic tubes or knobs in the attic or basement with cracked, brittle, or missing insulation
• A burning or hot-plastic smell with no obvious source
• Flickering lights that aren't tied to a bad bulb or fixture
• Rodent activity in the attic, since mice and squirrels chew insulation off wires and knob-and-tube has no metal conduit protecting it
• An insurance company asking for proof of updated wiring before renewal

Any one of these on its own isn't necessarily an emergency. Several together, or a smell of burning, is a reason to shut off power to that circuit and call someone right away.

What happens if you wait too long

The cost of ignoring old wiring tends to show up in three places. First, insurance: a lot of homeowners find out their policy is at risk only when they try to renew or switch carriers, and by then they're on a deadline instead of making a planned decision. Second, resale: buyers and their lenders often flag knob-and-tube during inspection, and it can slow down or derail a sale in Bonner and Kootenai counties just as easily as anywhere else. Third, and most serious, is fire risk that grows quietly. Insulation added over the years, rodent damage, and old splices don't announce themselves. The failure point is often invisible until it isn't.

Cost-wise, a planned rewire is almost always cheaper than an emergency one. A full home rewire can run anywhere from the mid four figures to well over $10,000-15,000 depending on the size of the house, how accessible the walls and attic are, and whether drywall or plaster repair is needed afterward. That's a wide range, and it's meant to be, because log cabins, additions with tricky access, and multi-story older homes all price out differently. Doing it as a planned project, room by room or circuit by circuit if budget requires, is usually far less disruptive and less expensive than doing it after a breaker panel failure or a scare with smoke in the attic.

If you're not sure how much of your home still runs on knob-and-tube, or whether what you have is a contained situation or a whole-house problem, an inspection is the place to start. Sageland Electric has been doing this kind of evaluation and rewiring work in cabins, farmhouses, and older homes across North Idaho for more than 21 years, and can walk you through what's actually there and what order to tackle it in.