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Is it safe to purchase a home with knob and tube wiring?

An electrical inspection revealed the house was predominantly knob and tube.  The quote to rewire the K&T was $20k+ not including patching the holes in the walls.  I'm hearing its common to still see some K&T in this part of town.  However, I'm also hearing that the few insurance companies that covered homes with K&T are either dropping customers or no longer issuing new policies if the house has ANY K&T.  Should we start looking in a different part of town or just demand the seller removes it before closing if we find another place we like that has it?
  • August 15 - US
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Answers (4)

Pasa, that's an excellent summary. Two thumbs up.

Electricians are always going to want to replace the stuff, and you don't want any unsafe conditions on the property. Insurance really isn't an issue, though; the surcharge is generally quite small.
  • August 15
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Profile picture for blue screen exile
There are only a few issues with knob and tube wiring:
1) No ground; may be an issue for some computer equipment, some air conditioning equipment, and the required GFI receptacles in the bathrooms.  Those few outlets can be run separately from the panel, assuming you have crawl space underneath, or attic space above.  It is typical to install Romex for those.  The code also requires the bathroom receptacles to be on circuits not shared with other rooms, so you would need to add that wiring regardless if not already done.

2) People like to "blow in" insulation into attic spaces.  The knob and tube wiring is designed to "air cool".  The insulation can cause problems with not letting the heat out.

3) If the receptacles and lighting sockets haven't been changed for a while, the connections at the devices can get "loose" causing heating.  This can damage the insulation where it enters the box.  The devices should be checked, and the insulation on the wires entering the box should be checked.  It is possible to repair the insulation with heat shrink tubing.

4) Though ceramic tubes are used through studs and sill plates, the tubes into the boxes are a varnished asbestos tube.  They technically are considered "hazardous waste", but they don't get in the air if left in place, so there are no safety issues.  They have very good heat resistance properties.

5) If there are rodents in the attic space, they have been known to eat the insulation off the wires.  The condition of the insulation should be checked.

6) Some people replaced fuses with circuit breakers but didn't realize that most of the knob and tube wiring was #14 instead of #12.  If #14 (CU) , it needs to be protected by a 15 amp breaker, NOT 20 amps.  Some people are careless and put 20 amps in instead.

7) Hot and neutrals are not always properly labeled, and sometimes they are wired reversed at outlets and light fixtures.  Sometimes the neutral is switched instead of the hot, and that is not acceptable in the U.S.  It is not hard to fix, but it can take a bit of time to check.

8). If run in the attic space with no flooring, some people end up stepping on the wires, which could damage them, or pull them loose from the knobs.

9) In the 1950, aluminum was starting to be used instead of copper.  The aluminum when oxidized becomes an insulator, thus causing heating problems at connections.  There are special connectors available for aluminum, but they are quite a bit more expensive than copper.  The wire also has to be sized up one size if using aluminum instead of copper.  And due to the thermal coefficient of expansion, the lugs at breakers can loosen if the wire is aluminum, causing additional heating problems.  If aluminum ALL connections need to be checked.  Aluminum may be a good reason to replace existing wiring.

Though it is really easy to install new outlets in walls and run new Romex in the craw space below., and easy to install new Romex to light fixtures through the attic space (if no attic floor), running new wiring to the switches can be more problematic due to fire blocking (hence maybe a need to cut open walls, or at least more holes in walls), and running to light fixtures on the first floor of a two story house can be more problematic.  Usually it is easier to pull floor boards than to gut and patch the ceiling properly so that it doesn't crack out again in the future.  But a nice finished hardwood floor?  Probably don't want to be removing the floor-boards.  Depending on the direction of the wires and direction of the floor joists, fishing in the wire may be an option.

$20k sounds high and excessive, but it really depends on the size of the home, how much access there is, and how much work one is doing.

It is legal to do repairs on knob and tube, and knob and tube still meets the code, but not for new work.
And original splices are all soldered connections outside of boxes.  No electrician does the soldering anymore, and splices now are supposed to be in boxes.

Though overhead wires to the garage are legal, I personally would rather see that put underground.
  • August 15
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Profile picture for pattylemme
You could see if the seller would be willing to help to share the cost of replacing the old system. They'll run into the same issue with other buyers, their agent will have to disclose the problem to everyone. Hopefully their agent will explain how serious an issue it is and you can all come to terms about it....good luck!
  • August 15
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Profile picture for wetdawgs
There are insurance companies who will insure knob and tube, so you'll need to make the decision for yourselves and your willingness to take it on.    "demanding" a $20,000 upgrade on a home that works perfectly well is not likely to go over well.

  • August 15
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