Insulating with *Updated* (an oxymoron, right!) knob and tube wiring

Hi everyone,

I live in New York State and haven't been able to find good information on whether or not we can get our house insulated.  I've searched the forums and internet, so please excuse me if I'm missing something obvious.  

We have a 1929 house, but the trick is that we don't have the original K&T wiring.  The electrical system was updated a few decades ago (100 amp) and from what I understand, we have new wiring but have some junction boxes in the wall that still have some K&T.  It's a weird hybrid system, where it was probably cheaper to have it that way than to remove every bit of K&T.  

Any idea if it's safe to have insulation in the walls with this configuration?  Any references you could point me to?  

Thanks so much!!

Best,

Ethan

Tags: Knob, and, code, insulation, tube, updated

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One more thing - our attic was insulated before we got the house, so how was this done if K&T is an issue???

Hi Ethan,

(my opinion) All wires have a temperature rating and K&T wires were not rated to be covered with insulation.  Since all K&T was not removed, you don't know where the old wiring is and is not.  Until that is determined no insulation can be added and then only where it does not cover the old wiring.

The previous insulation was probably not permitted (may not have required a permit) or inspected.  A proper home inspection when you purchased should have explained these concerns.

Here is an article:

http://www.greenbuildingadvisor.com/community/forum/general-questio...

And here is a link from that article:

http://artisanelectric.net/blog/tip-of-the-day/knob-and-tube-wiring...

Bud

Hi Bud,

Thanks for the info.  Unfortunately, our home inspector did not talk about K&T much, other than pointing out a couple places in the basement and attic where there was exposed K&T and pointing out that our electrical service had indeed been updated and that we had a modern fuse box and fuses, etc. 

I'm now thinking that the best bet would be to have an electrician come in and do a thorough survey of the house. 

Thanks so much - I appreciate the help.

Ethan

 Ethan . . . 1929 is pretty late for knob and tube in new construction; it would be possible for a home inspector or even some electricians who are not experienced in homes of this vintage to mistake the heavy fabric jacketing on some types of wire that actually contain both conductors for K&T. 

    BPI says we can't insulate where there is any concealed knob and tube.  This has resulted in a bumper crop of old wives' tales that need periodically to be reviewed. 


    In the 1970s and 80s hundreds (probably thousands) of old homes with knob and tube (including our first home) were insulated with UFFI or cellulose.  (Thank heavens mine was done with cellulose).  I am not personally unaware of any resulting fires in those houses, but I have more than once visited homes where open blown cellulose over early recessed lights that were not designed to shut off if the can got hot.

I discussed this subject with a friend who was a retired fireman.  He reported that exposed k&t in a fire has injured firefighters when they touched both wires at the same time, but he did not remember a single case where k&t actually caused a fire.  He went on to say "For Pete's sake!  Knob and tube conductors are separated by a foot or more as they run through the wall; romex conductors are sealed together in the jacketing.  One overzealous whack on a cable staple combined with normal movement by wind and framing shrinkage and you've got serious potential for a short and a fire." 

Some people argue (I was actually taught this and fell for it for a while) that K&T does not have the capacity to serve our heavy loads of TVs, hair driers, refrigerators, and so on. 

To this I reply "HORSE FEATHERS!!"  K&T wiring is 12-gauge.

There is one *genuine* concern:  sometimes connections for outlets, lights, and so on were made by twisting conductors together and using a black tape.  This has been done more often by modern "improvers" of the original wiring than by the original installers, but one can argue that there *could* be an arc.

I suggest that we weigh the benefits of cellulose (or fiberglass) insulation against the very small potential for a problem.  We are leaving undone work that will actually make homes safer, more comfortable, and more efficient, while benefiting the environment and providing one more tiny but essential step toward prolonging the habitability of the planet.

We take a far greater risk every time we cross the fracking (OOOPS!  I meant "fricking") street.

   

I did a Web search on this recently;

NEC prohibits covering K&T with insulation.  Must maintain a 3" air gap.  Some states, under the auspices of Bonneville Power, have amended that rule;  Calif, OR, WA, ID and also Nebraska.  There may be others.  Those new rules call for inspection by licensed Electrician, testing of load on circuits and sign-off by the Electrician.

Please note: this is only for flat attics.  In all cases, insulating wall cavities with K&T was not allowed.

Ditto on the fire starting stats.  Very few fires are started by K&T

Personally, I'd think about the lack of a ground wire and have all the K&T replaced. Good electricians are very good at tracing, testing and replacing wires in closed wall cavities.

Thanks everyone.  It does seem like K&T unfairly gets a bad rap for safety, when alterations or overuse can be causes of fire but not normally functioning K&T.  

We got a wood stove this season and it does a fair job heating the house.  However, it's easy to tell that a lot of cold is getting in through our walls so I'm just extra eager to see the efficiency improvement after insulation.  (Our kitchen and dining room cabinets that are right against our rear wall are almost as cold as our refrigerator!)  So Ed, I'm right on board with you about the benefits.  Insulation is a no-brainer and especially in Syracuse it's so important.  

Best,

Ethan

Ethan . . . insulation is only the half of it:  it's especially important to do a good job of air sealing.

If your wood burning stove takes its combustion air from inside the house, infiltration from inadequately air sealed details will bring in one cubic foot of cold, dry outside air for every cubic foot of air that goes up the chimney.

That is very true!  We had a residential energy efficiency contractor come in (same people who found the K&T then turned tail and ran!) and it seemed like they took more of a "cookie cutter" approach.  They wanted to do wall insulation, they checked that the attic insulation was good, they wanted to seal something in the basement, and they did a door blower test.  But other than that, they didn't seem to look at the leakage of the house or do anything to improve it.  Maybe there's nothing else to do other than replacing windows?  I would think a thermal camera could be useful.  

Anyway, maybe I should find a better contractor eventually when I'm ready to get serious about both insulating and sealing after the K&T is taken care of.  

Our fire place has an ash shoot - a little passageway down to the basement that I can open or close.  Perhaps when the house is sealed up better, opening that shoot will allow outside air to come in through the basement to fuel the stove (since our basement is leakier than the rest of the house) and that will be more efficient since cold air won't be moving through our living spaces.  

I know passive houses are so airtight that they have to have an air exchange system, and that they have heat exchangers, too, to heat the incoming air with the outgoing air.  Cool stuff.  

Thanks, everyone, for your input!  

 

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