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K&T wiring and insulation


Ken Meyer
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This is in a crawl space. My question is: if the insulation batts were to be turned around so that the vapor barrier faces up toward the heated space as it should, would the K&T wiring have the free air space it needs to dissipate heat? The condition is unsafe as it is now, but can it be remedied by simply reversing the insulation?

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Yes, If the insulation were turned the wiring would be ok. The insulation must be installed with the barrier side against the floor, not just facing the floor. It does absolutely no good to install insulation on the underside of joists unless you can completely seal it around it's entire perimeter so that no air can cycle through the cavity. Short of gluing it in place at 100% of its perimeter; there's no way you can get paper-backed batting sealed at 100% of the edge.

So, batts installed on the underside of the floors with the paper facing away from the floor are not only a fire hazard and liable to produce a surface where moisture can condense, they provide almost no insulation, whereas, even if you've only got 75% of the surface of the insulation snug against the floor, it's being 75% effective, isn't likely to trap moisture, and it doesn't present a fire hazard versus almost none with the batts installed on the bottom of the joists.

ONE TEAM - ONE FIGHT!!!

Mike

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No, I don't think that it would be OK from the standpoint of air movement around the K&T.

The K&T would not have any more and most likely less airflow around it if the batts were reversed. As far as the batts being installed improperly, Mike nailed it on the head.

I would also tell my client that they might find it difficult to get homeowners insurance with K&T wiring. SPECIAL NOTE IF YOU ARE IN KENTUCKY!!! You might need to get permission to say this from the State Board![:-dunce]

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Hi Scott,

I personally wouldn't be concerned seeing fiberglass wool from batting against K & T. Think about it, the insulation is not flammable; it's fiberglass, it has air circulating around it that will cool it quite quickly. In fact, it will probably draw more heat off the wire than cause the wiring to overheat. I've seen a lot of fiberglass installed against recessed ceiling fixtures and up against exhaust vents over the years and have always touched it to see just how hot it actually gets. It's never more than luke warm because it cools so rapidly with all of the air that moves through it. I'd say the same thing about rockwool.

On the other hand, there are other insulations that I think will cause it to overheat, such as SilvaWool and Cellulose and I can't imagine that any foamed-in-place stuff would do it much good either. More than once, I've crawled through attics with blown-in cells, encountered a warm spot on the cells, scraped it back and found a K & T splice that was overheating and had charred the surrounding cells. Thank goodness for the borate that the cells is treated with.

Oh, by the way; here's a shocking bit of news - there are literally hundreds of thousands of homes around here with insulation covering the K & T wiring. The PUD even had an inspection program in place when they were soundproofing the homes around the airport. They'd send electrical inspectors out to look at the K & T. Those inspectors would then, depending on its condition, either approve or disapprove covering the K & T with blown-in cells and post a certificate right there in the attic giving the work crews permission to cover it. Pretty bizarre, huh?

ONE TEAM - ONE FIGHT!!!

Mike

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Thanks, it makes sense that since the fiberglass is not flammable, it might be okay, but I wanted opinions from seasoned inspectors.

I discovered this situation during a WDO only inspection, but it needed to be commented on. The homeowner had done the insulation himself years ago. I'll give him the news.

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Originally posted by hausdok

Yes, If the insulation were turned the wiring would be ok. The insulation must be installed with the barrier side against the floor, not just facing the floor. It does absolutely no good to install insulation on the underside of joists unless you can completely seal it around it's entire perimeter so that no air can cycle through the cavity. Short of gluing it in place at 100% of its perimeter; there's no way you can get paper-backed batting sealed at 100% of the edge.

So, batts installed on the underside of the floors with the paper facing away from the floor are not only a fire hazard and liable to produce a surface where moisture can condense, they provide almost no insulation, whereas, even if you've only got 75% of the surface of the insulation snug against the floor, it's being 75% effective, isn't likely to trap moisture, and it doesn't present a fire hazard versus almost none with the batts installed on the bottom of the joists.

ONE TEAM - ONE FIGHT!!!

Mike

Mike, sorry if I seem dense, but I don't quite understand the second paragraph. Do you mean that reversing the existing batts and getting 75% of the surface of the insulation snug against the floor would be 75% effective? I'm having a hard time making that idea mesh with what you said in the first paragraph about when you said it does absolutely no good to install insulation under the floor unless it can be sealed 100%.

What is the right way to do it if starting over from scratch? There is no vapor barrier on the ground under the crawl, I already told the homeowner he should clean out the crawl and install a vapor barrier on the ground.

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OK,

I'll take another shot at it. If you install batt insulation on the bottom of the joists you've got a gap between the top of the insulation and the underside of the floors. If any air is leaking into that enclosed joist bay from below the insulation the insulation is useless and the money spent on it was wasted. The only way to make insulation installed on the underside of the joists work is to seal the edges of the insulation 100% where it's attached to the underside of the joists and at the ends of the rafter bay in order to create a large dead air space. To work, no air from the other side of the floor, the ends of the joist bays or below the insulation can be allowed to get in there. What's the likelihood of achieving that?

Even if they try to achieve that, they end up bringing the joist bay partly into the conditioned space of the house. Now, moisture-laden air that's moving from warm to cold and moist to dry is going to pass through that joist bay and attempt to move through the insulation. In doing so, that moisture-laden air will cool to dewpoint as it nears the vapor barrier (cold) side of the incorrectly installed insulation and it will condense inside the insulation and drip onto the paper below. Since there's very little air movement there to remove the moisture, you've created an ideal environment for growing mold.

Okay, so what's with the 75% effective? Well, if your installer orients the insulation correctly, with the vapor barrier side against the underside of the flooring, but does a poor job and only manages to get 10% of the insulation snug against the underside of the floor, then the insulation will only be 10% effective at doing what it's supposed to be doing. Even that, might do more good than installing insulation upside down on the undersides of joists with a huge air gap between the insulation and the floor above. If he manages to get 75% of it placed correctly, than it's 75% effective. If he does a really good job and ensures that 100% of it is placed neatly and snuggly against the floor, then it will be 100% effective at doing what it's supposed to be doing.

However, don't get this confused with R-value and insulating efficiency. I'm talking about installation effectiveness - that's a horse of another color and deals with how efficient the insulation is at resisting heat loss. You could still have only 75% of the floors correctly insulated to, say, R19, and you might still save more energy than an identical home where 100% of the floors are correctly insulated with R11, because the amount of heat saved over that 75% area is greater than the amount saved in the other house. We're only talking about installation technique and the effectiveness of it here.

ONE TEAM - ONE FIGHT!!!

Mike

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Sorry I did not get back sooner but I had to watch our Titian's give a game away to the Chargers!

The insulation is a Red Hearing, so to speak. It is a problem in it's own right but the K&T in my opinion is a larger issue, as it is an old and outdated form of wiring.

The idea that reversing the insulation would be OK, does not work. Fiberglass is a poor thermal conductor, one of the reasons it is used for insulation. Look at a "B" vent and the required airspace around one. Insulation is not allowed to be in contact with a "B" vent because the lack of air flow around that point of contact could allow for it to overheat. Fires have been caused when insulation around a "B" type vent has channeled the heat from the pipe to nearby wood framing.

I would caution the client about the insulation being installed wrong and then about the K&T. They also need to know that getting insurance on K&T is difficult.

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Originally posted by Scottpat

Fires have been caused when insulation around a "B" type vent has channeled the heat from the pipe to nearby wood framing.

Really? I'd sure like to see the stats on that, 'cuz I've never heard of it happening. In fact, I think that a steel separation plate or guy connected directly to a vent would transmit more heat to the adjacent wood than fiberglass, which is as you say a poor conductor, can.

That's a different topic, though. This one is about the insulation.

ONE TEAM - ONE FIGHT!!!

Mike

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Hey Scott,

I have something to add to this thread, but I'm waiting for permission from the KBHI before doing so. I've filed the appropriate request forms, and should hear back sometime after the first of the year.

[:-censore <------Me, in compliance with the KBHI.

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Guilty of kidding.

You know, I see K and T covered with insulation all the time in old houses. Sometimes with ten or twelve inches of cellulose. I always write it up as a defect, but I also wonder how it's been okay for the five, ten--who knows?--years it's been surrounded by insulation.

Does anyone know the temperature range at which K and T self-immolates?

I did a house for a guy from England this past summer, and he said the UK passed legislation mandating the replacement of all K and T several years ago because so many houses were burning down because of it. I wonder why it doesn't happen more often here?

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I always tell folks to simply get rid of it for all obvious reasons. I also have some other experience w/the material that bears consideration.

Back in earlier 80's, I was taking a class in electrical inspection put on the by the State of Michigan. 2 days of the class was Fire Science Fundamentals. We sat around for 2 days trying to start electrical fires; it was really cool.

One of the experiments was testing #14awg wire. We took a single strand of #14 bare copper wire, wrapped it in tissue paper, wrapped that in newspaper, and then enclosed the entire thing in a fireproof box w/an interior temperature of 120degF. We hooked up the ends of the test wire to an amperage/voltage generator, and cranked a continuous 30 amps through it (fully twice it's rated ampacity) and left for the evening. When we came back in the next day, we shut the system down, opened up the box, unfolded all the paper, and looked it all over.

The tissue was not even slightly discolored, and honestly, the wire didn't even feel warm; at least, it didn't feel any warmer than the 120 temp in the box.

What all this tells me is the NEC is extremely conservative.

That said, I still tell folks to tear it all out, usually because there have been alterations, and I just happen to think it's a good idea to get rid of old wiring that's been improperly tinkered with.

As far as why there aren't more houses here that burn because of K&T, I have no idea. I honestly don't think burying it in insulation means anything at all, but I'm not going to contradict the authority that says it's wrong.

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Originally posted by hausdok

OK,

I'll take another shot at it. If you install batt insulation on the bottom of the joists you've got a gap between the top of the insulation and the underside of the floors. If any air is leaking into that enclosed joist bay from below the insulation the insulation is useless and the money spent on it was wasted. The only way to make insulation installed on the underside of the joists work is to seal the edges of the insulation 100% where it's attached to the underside of the joists and at the ends of the rafter bay in order to create a large dead air space. To work, no air from the other side of the floor, the ends of the joist bays or below the insulation can be allowed to get in there. What's the likelihood of achieving that?

Even if they try to achieve that, they end up bringing the joist bay partly into the conditioned space of the house. Now, moisture-laden air that's moving from warm to cold and moist to dry is going to pass through that joist bay and attempt to move through the insulation. In doing so, that moisture-laden air will cool to dewpoint as it nears the vapor barrier (cold) side of the incorrectly installed insulation and it will condense inside the insulation and drip onto the paper below. Since there's very little air movement there to remove the moisture, you've created an ideal environment for growing mold.

Okay, so what's with the 75% effective? Well, if your installer orients the insulation correctly, with the vapor barrier side against the underside of the flooring, but does a poor job and only manages to get 10% of the insulation snug against the underside of the floor, then the insulation will only be 10% effective at doing what it's supposed to be doing. Even that, might do more good than installing insulation upside down on the undersides of joists with a huge air gap between the insulation and the floor above. If he manages to get 75% of it placed correctly, than it's 75% effective. If he does a really good job and ensures that 100% of it is placed neatly and snuggly against the floor, then it will be 100% effective at doing what it's supposed to be doing.

However, don't get this confused with R-value and insulating efficiency. I'm talking about installation effectiveness - that's a horse of another color and deals with how efficient the insulation is at resisting heat loss. You could still have only 75% of the floors correctly insulated to, say, R19, and you might still save more energy than an identical home where 100% of the floors are correctly insulated with R11, because the amount of heat saved over that 75% area is greater than the amount saved in the other house. We're only talking about installation technique and the effectiveness of it here.

ONE TEAM - ONE FIGHT!!!

Mike

I see where the confusion is coming from. I thought my photo showed it clearly, but maybe I should have explained it better. The insulation is currently installed between the floor joists, not below them, so if it was reversed, it would fill the joist bays and the barrier would be right up against the subfloor. They would have to support it with lath or something like that to keep it in place.
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Originally posted by hausdok

Originally posted by Scottpat

Fires have been caused when insulation around a "B" type vent has channeled the heat from the pipe to nearby wood framing.

Really? I'd sure like to see the stats on that, 'cuz I've never heard of it happening. In fact, I think that a steel separation plate or guy connected directly to a vent would transmit more heat to the adjacent wood than fiberglass, which is as you say a poor conductor, can.

That's a different topic, though. This one is about the insulation.

ONE TEAM - ONE FIGHT!!!

Mike

I have only found it once and it was with a metal "B" vent for a vertical furnace in a closet. I know that Dale Feb has pictures and documentation on it. Perhaps Bob Harper might have some as well.

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Agree, agree, and agree, Kurt.

There was an article in JLC a few years ago, in which the engineer/author recounted similar experiments to what you described. His results were identical. I remember him writing, "From a Physics point of view, wire gauges can withstand much more amperage than they're rated for . . . "

As for knob and tube, I always err on the side of prudence, as well, when 'splaining the stuff to clients. But I see it buried in insulation all the time with no adverse effects. The wiring between the floor joists in the photos? I'd make an issue if it were touching the insulation or the vapor barrier. But in real time? Expressed as a percentage, to what degree would heat dissipation be affected if the upper eighth of the wire were touching a piece of insulation or anything else?

I mean, look at Ken's photos. How much is heat dissipation decreased by encapsulating the wires within the ceramic tubes? I'll bet the coefficient is higher than encapsulation by loose-fill insulation.

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It's not that the K&T is going to burst into flames because it is covered or it is insulated. The natural rubber coating on the wires degrades quicker in heat. And with the newest K&T being around 60 years old it needs all the help it can get.

In Ken's photo the insulation is installed wrong and it has K&T. The largest problem is the K&T and that is due to it's age and what you can't see. The insulation is an added bonus. All of this is my humble opine!

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Originally posted by Scottpat

The natural rubber coating on the wires degrades quicker in heat. And with the newest K&T being around 60 years old it needs all the help it can get.

Not contradicting, but......

The old rubber on the K&T hangs there just fine until someone starts messing with it.

The real problem w/K&T is when folks that don't know what they're doing start messing with it. I've seen "qualified" electricians yanking on the loom & mangling it in general, and then folks exclaim how the rubber insulation is deteriorated and falling apart.

I've worked w/K&T my entire life; it was the defacto wiring in my Mom's 1850 house, and I've seen it in every conceivable configuration, in addition to cleaning up the slopjob alterations previous generations perpetrated upon it. If it is handled carefully and gently, it's surprisingly resilient.

Folks think it just bursts into flame in midrun or something. It doesn't. Like anything else, the real problems come from multiplied and compounded stupidities.

And finally, if memory serves, I recall Douglas H. telling us on several occasions his house is full of it and he thinks it works fine if one doesn't mangle it; this from the guy who brought us the warnings on Stablok panels.

(Apologies to Douglas if I've misinterpreted or misquoted him.)

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Last word from Redwood Kardon at our ASHI Fall Seminar is he's now promoting just simply replacing any K & T.

Until very recently, he was on the same page with Doug H. The K & T wires are strong, high quality and durable. Why replace them if they ain't broke.

But now, he's saying it's simply an age thing. All things will tend toward decay. K & T is just too old.

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Nationwide and State Farm may not insure a home that has K&T (not without a few strings attached anyway). I've heard that they will insure the home as long as it doesn't have more than X amount of K&T, as long as the client agrees to replace it in a years time, after inspection by an electrician yada, yada yada.

In my report I tell the client to make sure they can get insurance before signing on the bottom line.

Also, if memory serves, we had a pretty good discussion about K&T years back. May want to search K&T here for more information.

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I agree w/everyone on this point. Exclaiming on the wonders of keeping old stuff going is all academic. And, I've yet to see any K&T that hasn't been improperly altered, and therefore screwed up.

Toss that against the NFPA study that says any wiring system >40 years old probably has major defects kinda puts the nail in the coffin.

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I'm not arguing, either. But it's instructive, at times, to think slightly outside the box and wonder how the rules became the rules.

Every 120-volt circuit in the panel of this morning's house was overfused, but you'd never know it by looking at the wires. They were pristine. To me, that's curious and interesting.

I trashed the panel just like I trash K and T, but I don't ever want to find myself where I stop asking, "Why?"

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Originally posted by SonOfSwamp

one genius local HI wrote something like this into a report: "Should be OK if it doesn't bother the insurance company." (Where do we get such men?)

WJ

I guess if he's a genius, he scores pretty high up on that IQ chart. What happened to that chart, anyways...

At least he's not using H.I. school boilerplate.

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Originally posted by Bain

I'm not arguing, either. But it's instructive, at times, to think slightly outside the box and wonder how the rules became the rules.

Troublemaker.

Every 120-volt circuit in the panel of this morning's house was overfused, but you'd never know it by looking at the wires. They were pristine. To me, that's curious and interesting.

The wires that you see usually aren't the ones to be concerned about. It's the ones you can't see, particularly the ones above ceilings, just over light fixtures. Overcurrent protection is a weak-link kind of thing.

- Jim Katen, Oregon

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