Knob and tube is a form of electrical wiring used in the late 1800s and early 1900s, with a rubber sleeve covering the wires and porcelain knobs to prevent them from touching the wooden components of your home. It is often considered a fire hazard, especially if insulation is blown in around it. (source)
When we go through a house with a client, we look for knob and tube wiring in basements and attics. After buyers have seen it, once or twice, they easily spot it for themselves. But what does it mean for a prospective home owner if a house has disconnected knob and tube wiring? I got these questions from a client. Since she asked, chances are other people want to know, too.
…. I saw something yesterday with [a 4 Buyers Real Estate agent] with had visible knob and tube wiring in the basement in places, but it appeared to have been “cut” in those places.
Given that most of the places that I have looked at are older (usually built around 1910), I assume that most of them did once have knob and tube wiring at one point and that owners have since made an effort to replace the knob and tube, whether or not complete. These are my questions.
When knob and tube is “replaced” or “removed”, does that mean that it is completely eradicated or simply disconnected, cut, etc.?
Knob and tube wiring that has been cut in the basement indicates that the house once had that kind of wiring. Since the main electric panel is in the basement, and knob and tube wiring along that circuit is now inert and will cause you no harm.
Do insurers look with suspicion at existence of knob and tube that has been disconnected versus completely removed?
Insurance companies will rely on your home inspection as an inspection that has found active knob and tube wiring or not. So, disconnected knob and tube will not affect your insurance.
However, MassSave and the companies that install wall insulation may ask for a more extensive knob and tube inspection before doing blown-in insulation. The presence of disconnected knob and tube wiring, or old knobs in the basement may trigger the need for a knob and tube inspection.
How can one be sure that all knob and tube has been disconnected and/or removed if most of it is not visible and that some of it could be in other units, which even if one had the inclination to open up all the walls in one’ s unit, would be inaccessible?
You need an electrician to be entirely sure (which is why Mass Save requires the knob and tube inspection.) An electrician will need to look at all your overhead fixtures. By removing the fixture, the electrician can see the wiring. An electrician can identify two-wire outlets; those may be knob and tube or some other, older wiring. Then, remove suspicious outlets to see the wiring behind it.
Would there be any other potential way to find out about past history of knob and tube aside from opening up the wall or talking the owners (who probably owned subsequent to conversion to new electric)? Would such a conversion require permits that might be public record?
If the property had a complete rewiring, there may be a permit, but possibly not. If the replacement was done piecemeal, it is likely there will be no permit. Your best guess would be based on the overall condition of the electrical system. If the knob and tube is cut in the basement, then a lot of it is gone, maybe all of it. If the outlets are all grounded, that bodes well. If the old outlets in the baseboards are disconnected, that bodes well. If you can get into the attic and the wiring there is not knob and tube, that bodes well, too. If all these things look updated, you are likely to have little or no knob and tube.
On the one hand, I am disinclined to put an offer on a house where there is a possibility that knob and tube could create a problem. On the other hand, is it the case that disconnected knob and tube is the norm for a lot of houses around the area? I.e, would the vast majority of triple deckers in Somerville (which I cannot afford anyway) have disconnected (as opposed to removed) knob and tube?
Many, and possibly most of the housing built before 1930 had knob and tube wiring. It is pretty common. Electricians around here are used to finding it and replacing it. A couple of times a year, one of our clients will purchase a house with knob and tube and have it removed as soon as they move in. They buy insurance through a company that will sell it to them with a deadline for removing the knob and tube. If you can budget for that expense (figure $1000-5000), then the wiring should not deter you from buying the house. Grants are available to mitigate knob and tube wiring. Find out more about these grants in our Expanded Heat Loan Offerings.
Are there any other red flags, such as a circuit that has seem to be less loaded on it than usual? We couldn’t open up the electric box for the unit, but the adjacent unit did not have much on it.
You should never open an electric box unless you know what you are doing. Your inspector will do that, if your offer is accepted. He will show you how the box is wired and tell you what he thinks of it. He will also be checking for grounded outlets in the living spaces.