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Fix & Use or Abandon Wet or Submerged Knob & Tube Electrical Wiring
This article discusses the safety and reliability worries when knob and tube electrical wiring has been actually submerged by flooding or when it has been wet by leaks or even moisture rising in a wet or flooded building.
We include opinions on the minimum safe practices where K&T has been wet, and we offer renovation and wiring upgrade suggestions for flooded or wet knob-and-tube-wired buildings. Page top photo: water marks on this joist suggest that even though we see new plywood subfooring (at left in the image) this knob and tube electrical wiring may have been soaked by previous events.
This article series answers most questions about Knob and Tube electrical wiring.
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In particular, I recently read your section answering the question about submerged wiring, and your response “However, in most instances it is better and safer to replace the wiring." at KNOB & TUBE WIRING FAQs
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The International Association of Electrical Inspectors and the National Electrical Manufacturer’s Association appear to be in concert in firmly recommending against the re-use of any electrical wiring that has been submerged in flood waters, unless the wiring has been rated for wet locations.” and “Older wiring such as types with woven cloth insulation are much less resistant to water damage than newer PVC plastic insulated wiring, and should definitely be replaced if subjected to flooding.
Besides a google search for K&T (knob and tube) wiring and water damage or flooding, I also phoned five electrical contractors in New Orleans. They all highly recommended replacing any K&T wiring.
I am half owner of a century old upstairs-downstairs Victorian duplex with knob & tube wiring.
Last August, shortly after the downstairs tenants moved out, the upstairs tenant put laundry in the wash machine, turned on the machine, and left for a vacation. The machine failed to shut off the water. The back halves of both apartments were extensively flooded with probably a thousand gallons of water. The coved ceilings and some walls and some floors in the back half of the lower unit were beyond saving. It was two weeks before the downstairs ceilings were removed.
The ceiling bays contained horsehair padding under the subfloor above that was still dripping water. I could not find anybody then who knew what the horsehair mat was for. It was two more weeks before I decided to remove the horsehair since it was still holding water like a sponge.
A remediation company was hired, but they only dried out the upper unit. The remediation company apparently put multiple machine on one circuit upstairs. When they later moved the dish washer out of the way, they did not completely shut off the hose bib, causing even more water damage down stairs.
When they put their machines down stairs, they again put multiple machines on a single circuit which has not worked properly since.
My worker through it might be a breaker. He replaced the breaker, however that problem remains.
A couple weeks ago, the upstairs tenants asked for a rent reduction, primarily based on noise complaints, but they also included the fact that they now have intermittent electrical problems since the flood. This now raises the possibility of adding damage to the electrical system to the insurance loss claim.
Except for kitchen and main panel upgrades, and adding lines for clothes washer and electric wall heater, the K&T appears to be in early 1920’s “as built” condition.
When the coved ceilings gets replaced, it will be with a double layer suspended sheetrock ceiling with semi-flexible perimeter coving for impact sound isolation that hopefully will not need to be touched for another century. This will also entail filling the joist bays with fiberglass insulation for sound absorption. Any later electrical work in the ceiling would be difficult and very expensive.
The K&T wire here was not submerged, but it was definitely water saturated or near saturated for over a month. It was five or six months later before the apartment felt normally dry. Some links referred to water causing possible dry rot damage to the linen or cotton fibers in the K&T cambric covering.
My understanding is that dry rot is a fungus that needs organic material, moisture and air, and cannot grow in submerged conditions.
Everyone seems to agree that modern wiring should last and be trouble free for the next century. However, I have been unable to find a local electrician who will take a position that the current wiring is either unequivocally reliable after perhaps some trouble shooting and correction, or is sufficiently questionable and unreliable and should be replaced.
Assuming the information provided above is accurate, what would you recommend? Does the saturated K&T wiring above fall into a category similar to submerged or flooded requiring replacement? Or is there some test that could be done to determine such. - Anon by private email, 2017/03/25
Our photo shows improperly-extended knob and tube wiring in an attic as well as leak stains on the roof decking: was this knob and tube wiring ever wet? Was it damaged?
First: regarding your remark about observing " ... intermittent electrical problems since the flood."
That's very worrisome, since there are risks of both fire and shock when an electrical system is in troubl
e. Wet insulation or building materials can short wiring, for example. I know this may seem chicken-hearted, but if it were my house I would TURN OFF any misbehaving circuit right away until it could be traced, examined, repaired.
That's inconvenient for your price-haggling tenants but you might get away with a heavy duty extension cord for a time - (not under rugs etc or you'll create another fire hazard).
Of course the original wiring that kept hot and neutral apart, in air, with ceramic knobs and tubes preventing contact with wood or other combustible surfaces made this a nice wiring method, and of course most people understand by now that the absence of a ground conductor means the circuit can never be as safe as a newer grounded electrical circuit.
There are multiple risks with older K&T wiring, of which you've noted the experts warning about wetting the wire insulation and thus damaging it.
What's often not mentioned, although we do beginning at KNOB & TUBE WIRING are additional risks where knob and tube wiring (K&T) remain in use:
Our photo shows old knob and tube wiring as it was originally installed in an attic floor: note that the wiring runs in open air, not covered by nor buried in insulation.
I'd be concerned too about hidden mold contamination. You are not exactly right when focusing on the statement "dry rot ... cannot grow in submerged conditions"
I would absolutely NOT layer on more coverings on any wall or ceiling before first making a test cut opening or two in the most-suspect areas to double check that there's not damaged or moldy drywall (plaster is more mold resistant but not mold proof) moldy insulation, mold on wood framing, or rot or insect damage. It'd be hell to laminate more drywall then to have to tear it off to repair the building.
I would also NOT layer on more drywall before deciding if I needed to add electrical circuits, or to replace or abandon existing knob and tube circuits, for the same reasons; It's much nicer, and less expensive, when snaking new wires, to be able to make cuts wherever you need, knowing that the wall or ceiling will be covered over with more drywall later.
You'll have a hard time finding someone stupid enough to guarantee the safety of an old electrical circuit that they didn't install, know nothing about, and cannot see - or you'll find some dope, probably a smalltime contractor with no insurance, who might live on the edge and promise you more than a more-informed electrician would dare.
You'll also face the OTHER PEOPLE'S MONEY problem that contractors will take the safe path - which means spending more of your money to reduce their risk of a future complaint or lawsuit.
So spending your money on my worry: I would be reluctant to laminate more drywall and thus face that cost, before abandoning any and all questionable circuits; and I would add all new circuits (see my notes below) first too. Your comments make plain you know this so I'm really emphasizing it for other readers.
It's cheaper to do wiring first, as I noted. And it is likely that an older home needs more circuits anyway.
OK so if you figure for you it's not OPM its MM (my money) and you are still troubled by the circuit abandoning prospect, I would at a minimum do this:
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