The Truth About Knob & Tube Wiring

What is Knob & Tube Wiring

Knob and tube wiring came into existence in the early 1880’s in Canadian homes and continued to be used right up into the 1930’s. It was a dawn of a new era as we came out of the days of candles and lanterns and started wiring houses for electricity.

In the picture you can see the porcelain knobs that hold the wire in place along the studs as well as the porcelain tubes where the wires pass through the studs. Imagine back in the day when all these holes were drilled by hand!!

The joints were soldered together and thick cloth based electrical tape was used to cover the joints…a common area of failure over years of use, expansion and contraction, and heat generated from the overloading of circuits.

How to Spot Knob & Tube on Your Home Search

The first thing to be aware of is the age of  the home.

Looking at the image above you can see the home construction using “Lathe and Plaster” which uses thin 2″ slats of wood with 1/4″ spacing between each piece. A rough coat of plaster bound together with horse hair is applied over the wood slats allowing the excess to push through the 1/4″ spaces, securing the plaster to the wall as it dries. Unfortunately the horsehair over time breaks down and causes the integrity of the plaster to weaken and pull away from the wall, but that’s a topic for another blog post.

Lathe and plaster construction was the most common method of finishing walls used during the time knob and tube was in use. If you can identify this type of wall finish, it’s likely you should be searching for knob and tube wiring as well.

In today’s modern world and changes in electrical demands in homes, we’ve seen much of this older wiring being changed out and updated to newer wiring.

However…the cost of replacing knob and tube wiring can be cost prohibitive and often we find DIY’s and even electricians cutting corners and only replacing the most accessible wires. In fact in many of our flips we’ve seen newer romex wiring joined together inside the walls to knob and tube wiring with the use of wiring marrettes and electrical tape…a recipe for disaster.

The key places to look for knob and tube wiring in a home are…

  1. By the electrical panel where new wires go into a junction box and then out to knob and tube wiring.
  2. Look for junction boxes where wires go up into wall cavities to see new wires into the junction and knob and tube coming out
  3. In attic spaces where you’ll see the actual knobs and tubes (check with a tester to see if they are live)
  4. Look at old switches…especially push button switches and wall plugs with no ground. This is a sure sign of knob and tube.

Fact vs. Myth

The long standing myth is that knob and tube wiring is a fire hazard and although there is some truth to this, the overwhelming evidence proves that it can be safe and reliable.

However the concerns with knob and tube wiring are two fold…

  1. Knob and tube wiring doesn’t have proper grounding system
  2. The connection points in knob and tube wiring, over time, can become weak…a potential fire hazard

The trick is to ensure that the wiring is inspected by a licensed electrician as well as adding ground fault breakers or plugs to the circuits in your home with knob and tube wiring.

The Cost of Replacement

One of the biggest reasons for both homeowners and electricians to cut corners when replacing knob and tube wiring is cost…

The average home with this wiring usually has a smaller service coming into the home. The early systems were as small as 30 amps!!! This is the amperage that a typical electric clothes dryer requires to operate…not an entire home.

It’s been our experience that the majority of knob and tube wiring still existent in homes today, are on the second story due to the difficulty of replacement. Often it requires putting holes in existing walls to allow the running of new wires and attaching of these new wires to the outlets and switches throughout the second storey.

It’s not uncommon however in older homes to have all the original knob and tube.  Replacement of these older wires is often a requirement of insurance companies who feel it is too high of a risk due to grounding issues and fire hazards.

Our experience shows that the costs of  rewiring a home with knob and tube in our area can run from a low of  $2000-$3000 dollars and as high as $10,000. The cost is very dependant on how big the home is, how much knob and tube remains in the home, and the layout of the home which can often make it difficult to gain access, making replacement difficult.

How to Avoid Getting Stuck With Knob & Tube Wiring

Unfortunately the training to become a real estate agent doesn’t really cover how to look for knob and tube wiring. You would think hiring a real estate professional would be all that’s required, but unfortunately that’s not the case…unless of course you hire Dave & Steph (or an agent that has experience outside of the training provided by OREA). Hiring a professional electrician and having a professional home inspection done to look for knob and tube wiring among other things are always recommended.

We’ve been flipping houses for years now and have hands on experience with knob and tube wiring…in fact we’ve personally changed out thousands of feet of old wiring and know exactly what to look for when helping you buy a home.

Don’t hesitate to call us directly for all your house buying needs.



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Dave Vogt

Dave is a kick butt marketer, a hands on home renovator, a real estate investor, a Realtor®, and the Dave of The Dave and Steph Real Estate Team. Together with his partner Steph they are on a mission to change the way you think about the real estate industry by setting a new level of service and value!

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