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Should i buy a house with knob and tube

should i buy a house with knob and tube Tracking Down Knob-and-Tube Wiring | This Old House

This Old House: Tracking Down Knob-and-Tube Wiring

should i buy a house with knob and tube Should You Buy a House with Knob and Tube Wiring.

should i buy a house with knob and tube

d_green wrote:Prior work, however, seems like a real hodgepodge. Whenever I look around the basement I get worried. I see knob and tube wire in the basement that looks like it has a very brittle insulation. Junction boxes looks stuffed and some are left open because the wires don't fit inside. Essentially, every 2 prong, non-grounded outlet is fed by K&T. The overhead light fixtures are also all fed by K&T.

Yes, "hodgepodge" is a good way to describe what his basement electrical was like too. Several people made updates over many decades, all with good intentions at the time, but it was just time to wipe the slate clean and start fresh. Overfilled junction boxes are common, as is overloaded circuits when people decide to add receptacles/lights by splicing into those junction boxes. You could try and split the runs into a larger, or 2 junction boxes side by side, but generally speaking the K&T wiring is so brittle that if you tried to pull the wiring back to do so, you'd probably just create more problems than you're solving.

And you think the K&T insulation is brittle on the wires in the basement - HA! Try taking down a ceiling light fixture on the main or 2nd floor, especially a light that is used often... and you'll find out exactly how brittle and risky your wiring is. All of the heat from the incandescent lights in the ceiling fixtures rise, for the last 100 years, and cooks the insulation significantly more than anything you're seeing in the basement. e.g. If your kitchen lighting is a multi-bulb ceiling fixture and original K&T, I would bet the condition of that wire insulation will scare you.

d_green wrote:All of the second floor lighting fixtures and outlets could be reached from the attic. Electricians have in the past fished Romex from the basement to the attic and then branched off from there. I think the second floor could be done without much damage by fishing Romex down the walls.

Yes, that's exactly what we did. We pulled 3 new 15A circuits from the panel, up through an exterior wall (one of positives of old homes having poor insulation) all the way into the attic above the 2nd floor, and simply fished the 2nd floor plug receptacles down from above -- no plaster damage at all. Ceiling light fixtures was cake since we were right there too. And since we were rewiring the house and getting it inspected, NEC 2008 code requires all bedroom receptacles to be AFCI (arc fault) protected (special breaker in the panel), smoke detectors in each bedroom plus a smoke in the hallway outside the bedrooms - all hardwired together. So, it was honestly easier to just pull new home runs from the panel to the 2nd floor given the AFCI requirements.

d_green wrote:The first floor scares me though.
I also have no idea how you fish Romex to the first floor lighting fixtures without damaging either some plaster or tearing up the floor above.

The main floor ceiling fixtures are definitely the hardest to deal with. For his kitchen, he decided he wanted to replace the ceiling flush-mounted light fixture with recessed lighting. So, while installing recessed lights was more work (cutting ~12 5" holes is plaster ceilings *sucks*), it actually made fishing the new wiring much easier. His hardest issue to deal with was the dining room ceiling chandelier. We had to use a 6 foot long flexible auger drill bit (see video link below to get the idea), up through the existing light fixture box hole in the ceiling, and drilling across multiple ceiling joists and then fishing the new wire back. I'm not going to lie - this part sucked. We had to go more than 6' over, so he wound up getting a smoke detector strategically placed 1/2 between the chandelier box and where we had access to the ceiling cavity in the kitchen (e.g. drill over 6 feet, cut a 4" hole in the ceiling at that point, and drill another 6 feet over, filling the hole when done with a smoke detector).
I'm not going to lie though, we actually did accidentally drill up through ceiling and into the 2nd floor hardwood floor -- whoops. Luckily it came out under the master bedroom bed!


d_green wrote:So, if all we want done is just replacement of the remaining K&T and not adding any new circuits or outlets, I hope that won't cost K. Would we be required to do all of the things you mentioned you did?

I also don't understand some things about electrical inspections. How does a buyer or inspector or even the owner know if past electrical work done ever passed or was even inspected? How would an inspector know what work was done when and if it was ever permitted? Are the type and number of outlets in a house recorded somewhere officially?

From what you describe, likely less than k... but you'd need to get a couple contractors out for bids. My concerns would be what work they can do for sure w/o damage to the house... and more importantly, what parts they're expecting to likely have to cut some holes. As you already suspected, the main floor ceiling fixtures are the highest probability. You may want to have some creative ideas in the back of your head - like being open to some recessed lights in the kitchen, etc. Also, depending on what work needs to be done, that portion of the work must be brought up to current NEC code. So, for example, let's assume you're 2nd floor bedrooms are still K&T and you want it replaced. The electrical contractor would not only have to replace the K&T with romex, but would also have to AFCI protect that circuit, and install smoke detectors in each bedroom... since that is current code in most parts of the country (NEC 2008). So, whatever circuits you touch will not only need to be replaced, but also brought up to code. AFCI bedroom outlets, smokes in all bedrooms and hallway, 2 20A plug circuits in the kitchen, microwave on a dedicate circuit, disposal/DW on a dedicated circuit, etc, etc.

Your city hall's building department (code enforcement) should be able to tell you all permits that have been pulled for those house, what was inspected, and dates (going how far back - who knows). No, they would not have a count/inventory of how many branch circuits and receptacles your house has. Assuming you went forward with the K&T replacement work, you (or the contractor) would need to pull an electrical permit detailing out what parts of the home electrical you are touching/replacing - # of branch circuits, the service itself, etc. Once the work is done, the city building inspector would come onsite you your house to inspect the work and signoff on it. You'll normally get some paperwork and sticker that can be put on your panel, and they log the permit approval at city hall. You may need 2 inspections - check with your city... we only needed one, the final inspection.

d_green wrote: Also, say a home inspector sees some work that would have passed inspection many decades ago, but would not pass under today's code? For example, I know methods of grounding outlets and switches have changed over time. I'm not talking specifically about K&T here but even work done with more modern Romex. Can an inspector require you to redo stuff that passed 30 years ago?

When the permit is pulled, it will detail out what you're touching/changing. The inspector when he comes out to inspect can only inspect those items & he'll inspect it compared to today's code (most cities in the USA follow the 2008 NEC, but check with your city). So, let's say your permit is for replacing 10 branch circuits from the panel - he can only inspect/comment on the work related to those 10 circuits. The rest of the electrical is "grandfathered". Likewise, if you pull a permit for upgrading the service from 100A to 200A, his inspection is limited to the service and main panel... he cannot just randomly start spotting issues with the existing branch circuits.

should i buy a house with knob and tube Knob and Tube Wiring | Old House Web

The ceramic tubes will outlast civilizations. With certain important exceptions your K&T will outlast the house itself, unlike modern wire.

K&T is more heat resistant than the equivalent modern wire, because the conductors are separated by an air gap. The ceramic tubes mean that even if the insulation deteriorates it creates no fire hazard. And in fact, if you check fire statistics you'll find K&T wiring is as, or more, safe than modern wiring. Hammered nails or screws can create subtle shorts and sparks in modern wire, but have little to no effect even if they pierce K&T wires.

This resulted because there were no documented cases of a fire being caused by knob-and-tube wiring, whether insulation covered it or not.

Leaving light fixtures on K&T is especially practical, as grounding matters much less, and these are typically the hardest runs to replace.


That said, much K&T wiring is either overloaded by modern uses, or has been hacked to death by bad renovation. Our jurisdiction (Berkeley, CA) requires an inspection by a licensed electrician prior to insulating over Knob & Tube (see here).

It is important to check:

  • Fuses have been replaced with appropriate circuit breakers (15 amp for 14 gauge wire).
  • Modern splices are proper, and made inside junction boxes.
  • No branch circuit is overloaded (selectively add circuits to bring things in balance. Rewire your kitchen. Run separate new circuits for the dishwasher and laundry and any place within 6 feet of water).
  • Hot & neutral have not been mixed up between branch circuits.
  • If you have a shared neutral (common) be sure to have 2-Pole breaker (See https://diy.stackexchange.com/a/36456/5960 )
  • Insulating loom where K&T enters metal junction boxes is still in acceptable shape.
  • Ceramic knobs support individual strands of wire along their run and ceramic tubes protect the wire where it passes through wall studs or floor joists. Knob and tube wiring was state-of-the-art up until around 1950. If not abused or tampered with, knob and tube wiring is still capable of carrying electricity throughout your home.

    Knob and Tube Wiring Problems

    Knob and tube wiring is generally safe except in the following circumstances:

    • Brittle insulation – the insulation on the wire cannot handle high temperature environments, such as those found in modern ceiling-mounted light fixtures. If the wire has been inappropriately used for such an application, the insulation around the knob and tube wire will become brittle and break off, leaving exposed wire.

    • Improper splices – splicing into knob and tube wiring is not a straightforward process. While an electrician can do a proper splice, Pillar To Post® inspectors often find inappropriately splices which create a serious safety hazard.

    It is only appropriate for ungrounded applications.

    Do You have Knob and Tube Wiring?

    If your home was built prior to 1950, you may have knob and tube wiring and not know it. Most homes with knob and tube wiring have been at least partly upgraded. It is not unusual to find all new wiring at the breaker panel and old knob and tube wiring for the lighting circuits on the top floor of the home.

    Is it Safe?

    Knob and tube wiring is not inherently unsafe. Installations have to be evaluated on a caseby-case basis. Safety usually depends on the history of modifications and upgrades

    Home Insurance

    Most home insurance companies will not write new policies on homes with knob and tube wiring. If you are already living in the home and have a policy, you can simply have an electrician evaluate the system and correct any deficiencies. If you are buying a home, you will probably have to replace all the knob and tube wiring. The insurance company will insure you through the transaction but will require you to upgrade within a defined period of time.

    But the seller does not understand the fuss because they have home insurance already. The insurance will not likely chase down existing policies for upgrades, but they will take the opportunity with a new policy to request an electrical upgrade.

    Updating the Wiring

    If you only have a few knob and tube circuits to replace it will not be expensive. But if the home has knob and tube wiring throughout, an upgrade may involve more than just replacing existing circuits, and thus may present a greater expense. In an upgrade, the wiring will be replaced to today’s standards. For example, in the era of knob and tube wiring, a living room might have had only a single electrical outlet. Today, outlets are installed within six feet of any point along the wall. This probably also means you will need to upgrade the breaker panel to accommodate the additional circuits. In the end, it is generally well worth the expense to upgrade to a modern electrical system.

    S. built from around 1880 to the 1940s often still have knob and tube electrical wiring. This is where electrical wires anchored by ceramic insulating knobs pass through tubes placed inside holes drilled in the joists of the house.

    Financing a Home with Knob and Tube Wiring

    The Department of Housing and Urban Development (HUD) states that home appraisers should examine the electrical box to ensure there are no broken or frayed wires. They don’t usually examine whether the home has knob and tube wiring.

    Major selling guides (Fannie Mae, Freddie Mac & FHA) are ok with knob and tube wiring as long as it functions, is safe, in good condition and is a minimum of 60 amps. As long as an appraiser doesn’t state the electrical is in poor or hazardous condition there usually isn’t a problem with getting financing for the home.


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