# Insulating attic w/knob and tube



## Eldredgejason (Dec 4, 2010)

Apprentice with a question here...my landlord is doing a job where he wants to use spray insulation in an attic w/ knob and tube. I referred him to 394.12(5) in the nec that stated..."use not permitted...in spaces are Insulated by loose, rolled, or foam in place insulating material that envelopes the conductors." Any one have any suggestions on what he could do to do this job safely without having to replace the knob and tube?


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## danickstr (Mar 21, 2010)

You must change it to comply with code. 

But here is an article I read once, paraphrased, of course, as if I had written it, but I didn't:whistling2:

safely or to code? I really don't see a knob and tube wire carrying its maximum of 15 amps and getting so hot that it starts to decompose the rubber. The knob and tube that I see damaged is from people replacing 15 amp screw in fuses with 20 and 30 amp "improvements". that will hot up that wire.

In an attic on a hot day the ambient temp could be 130 degrees. Then run 15 amps of juice through a piece of old rubberized knob and tube and maybe there is a legit problem, but 14 ga wire never seems hot to the touch when I run 14.9 amps through it (15 should blow the breaker, I guess) At least not 130 degrees.


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## wayne g (Nov 28, 2010)

Article 394.12 (5)
The only way to make it comply is to remove it.
If he insulates he will be in violation.


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## Eldredgejason (Dec 4, 2010)

wayne g said:


> Article 394.12 (5)
> The only way to make it comply is to remove it.
> If he insulates he will be in violation.


That's what I was thinking...he doesn't want to be in any code violations, and especially doesn't want it to be unsafe. I was hoping there would be a trick out there of incasing the wiring somehow.


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## egads (Sep 1, 2009)

Besides the rule based on encasing conductors meant to be in free air, there is the problem of hiding those conductors. Anyone crawling in that attic in the future will have no idea where the wiring is.


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## Podagrower (Mar 16, 2008)

As you already know, K+T was meant to be installed in free air, and there really is no way to foam around it. I suppose you could use 2x4s and form a channel around the K+T, then when you remove it, it would be in free air again, but how much air is required? 

Knob and Tube in insulation is a very bad idea, and it can hurt when you find it hidden.


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## Jbird66 (Oct 26, 2010)

If he really wants to insulate he could always put a floor above the K&T or build boxes around where it is and insulate on top of that. Not the best way to insulate and it would be a ton of work.


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## macmikeman (Jan 23, 2007)

Jbird66 said:


> If he really wants to insulate he could always put a floor above the K&T or build boxes around where it is and insulate on top of that. Not the best way to insulate and it would be a ton of work.


It would be much less work to just replace it with a more compliant method prior to insulation rather than trying to floor over or box it in methinks.


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## garfield (Jul 30, 2009)

*Blown fiberglass*

Blown fiberglass and a floor installed above it wouldn't make me nervous....however the money spent on the floor and the more expensive fiberglass could be paid to some poor sparky for romex then use cellulose.


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## Dennis Alwon (May 9, 2009)

egads said:


> Anyone crawling in that attic in the future will have no idea where the wiring is.


I agree that insulation should not be put over K & T but I don't get this statement at all.


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## den (Mar 28, 2009)

The only house that I have been in that was foamed in the attic, the foam was sprayed on the inside of the roof and not on the attic floor where I assume the k&t is at. If that is the case I don't see a problem with it


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## Dennis Alwon (May 9, 2009)

den said:


> The only house that I have been in that was foamed in the attic, the foam was sprayed on the inside of the roof and not on the attic floor where I assume the k&t is at. If that is the case I don't see a problem with it


Many of the homes have had insulation in the attic long before the foam came into existence. So unless the insulation is vacuumed out it is in violation.

K&T also goes up the walls so any exterior wall with K&T that has been blown in is an issue.


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## den (Mar 28, 2009)

I had to remove some k&t last week so SIEDA (low income tax doars at work) could blow fiberglass insuation in. All of it was ran on interior walls except for one porch light was not used and was aready cut loose. Exterior walls would defintly be a violation. I was not sure how the foam was going to be placed which would make a difference.


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## Eldredgejason (Dec 4, 2010)

Can I replace knob and tube sections at a time?...put a box where the knob and tube come up...splice on to romex and run that across to slice back into the knob and tube at the other end?


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## Dennis Alwon (May 9, 2009)

Eldredgejason said:


> Can I replace knob and tube sections at a time?...put a box where the knob and tube come up...splice on to romex and run that across to slice back into the knob and tube at the other end?


Check out this section and article 394



> 300.16(A) Box, Conduit Body, or Fitting. A box, conduit body, or terminal fitting having a separately bushed hole for each conductor shall be used wherever a change is made from conduit, electrical metallic tubing, electrical nonmetallic tubing, nonmetallic-sheathed cable, Type AC cable, Type MC cable, or mineral-insulated, metal-sheathed cable and surface raceway wiring to open wiring or to concealed knob-and-tube wiring. A fitting used for this purpose shall contain no taps or splices and shall not be used at luminaire outlets. A conduit body used for this purpose shall contain no taps or splices, unless it complies with 314.16(C)(2).


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## electrictim510 (Sep 9, 2008)

danickstr said:


> You must change it to comply with code.
> 
> But here is an article I read once, paraphrased, of course, as if I had written it, but I didn't:whistling2:
> 
> ...


I don't think the issue is necessarily what the wire gets hot in normal conditions. I think the issue is more in the fact that the splices themselves, though soldered mostly, still are in direct contact with insulation and can potentially make a fire out of a simple bad connection a little easier. And we can not rely on the breaker always tripping at the rating marked on the breaker itself either especially with wiring that is exposed like knob and tube and also might still have a FPE or Zinsco breaker (aka notorious for not tripping off at the right amperage pulls.) controlling it


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## egads (Sep 1, 2009)

Dennis Alwon said:


> I agree that insulation should not be put over K & T but I don't get this statement at all.


Why? What I was thinking (and have experienced) is blown in fiberglass so thick it covers everything. You have no idea where the wires run and they are therefore hard to avoid. Now if the OP is talking about spray foam instead of blown in, then it could (perhaps should?) be put between the rafters, leaving the K&T exposed. (for a future electrician to replace)


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