General question:
If a house has K&T wiring, can insulation still be blown in?
I was thinking no because of the heat buildup in the antique wiring, but I don’t know for certain.
Apologies if this has been discussed before-I wasn’t sure how to narrow down the search criteria.
Thanks.
Maybe someday I’ll know a little something.
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Replies
There are some differing opinions about knob and tube wiring. Our house has k&t most of which is in excellent condition. In the attic, where you would expect the insulation to be dried out and brittle, it's in great shape. In the cellar, there were a few spots that were bare wire, probably chewed away by rodents. I've read about the concerns of heat buildup in the old wiring, but I don' t get it . Our insurance company inspected the house last winter and insisted that the wiring be updated to modern standards. No small feat in post and beam structure. Do some research.
Don't do it. It's a fire hazard.
Ask your local fire marshall.
(It also violates the NEC model code)
Youth and Enthusiasm Are No Match
For Age and Treachery
That's what I thought. I'm not doing it; my house doesn't have it. Someone at work asked me and got me curious. Thanks.
Maybe someday I'll know a little something.
Installing knob & tube in a space that is currently insulated violates the NEC. The NEC says nothing about installing insulation over K&T. This is why we don't get hit by state inspectors when they come in to look at subsequent work.
Should it be done? No.
Yes, that is the level of minutia that we deal with here in the great state of Washington.
"In 1987, an amendment to the National Electric Code (NEC) prohibited the placement of insulation in contact with knob-and-tube wiring."http://www.waptac.org/sp.asp?id=7190 (Interesting article)Different jusrisdictions can adopt their own variations, of course.
Youth and Enthusiasm Are No Match
For Age and Treachery
Thanks for the link to waptac article on this subject. It appears that the state of Washington and others have confirmed my belief that there should be no fire hazard from insulating around KTW, only from over-loading those circuits with additions and alterations, especially using oversized fuses. The fact that thousands of K&T-wired houses have been insulated without a single instance of fire resulting, is especially comforting for me, since I insulated the attic of my 1940 K&T-wired cabin 20 years ago.By the way, do today's copper-clad pennies work as well in fuse sockets as the solid copper ones did? ;)BruceT
>>The fact that thousands of K&T-wired houses have been insulated without a single instance of fire resulting,Probably hundreds of thousands.But I don't buy the "no instance of a fire."I've spoken with too many firefighters and marshalls, and seen too much K&T with very brittle and/or failing insulation which has been covered with thermal insulation, to accept those claims.But maybe I'm allowing my prejudices to overcome my reasoning.
Youth and Enthusiasm Are No Match
For Age and Treachery
seems ironic that most of the houses that would benefit from a good dose of blown-in cellulose would be the same ones likely to have K&T wiring, and thus unsafe. How are people insulating these old places??Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
>>How are people insulating these old places??Most often badly, or not at all.I don't know of a good answer except "rewire."
Youth and Enthusiasm Are No Match
For Age and Treachery
That's what eventually happended in my old house. Cellulose was blown in stud and attic bays ignoring the K&T. Since the K&T was in very good condition, I tried to leave two circuits for just lights (they are quite...circuituous, sorry). When I opened a wall for a new shower I found both circuits coming in and out of the hall light switches, so away they went with the rest of the K&T.
Of course, the wiring that bothered me was the newer NM stuff the previous homeowner hacked in (what's this bare wire for? Just cut it!). Thanks to some 1917 upgrades, I found a coupe of interesting newspapers in my attic....that's not a mistake, it's rustic
Can you explain more about the fire hazard? K&T wiring is solid copper of the same gauge as romex, carrying the same or probably lesser loads as romex circuits, the hot and grounded wires are separated three inches apart vs Romex bundled close together, so why would there be more of a fire hazard if they were covered with insulation than with Romex, which is routinely covered by insulation?BruceT
My understanding is that K&T's amperage rating is based on its ability to dissipate heat.Which is, I believe, related to the type of insulation which is damaged by excessive heat.
See, also, the link in the next message
In my own work on houses with K&T, the most likely place to find damaged insulation is above ceiling fixtures, which often become too warm from over-lamping.
Youth and Enthusiasm Are No Match
For Age and Treachery
Edited 10/1/2006 8:57 am ET by rjw
An alternative would be to place unfaced batts in the attic and leave space around connections. Yes, I know that this stinks thermally, but it's way better than no insulation.
IMO, I wouldn't blow cellulose fiber over the k&t.
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"Doubt is not a pleasant condition, but certainty is absurd." Voltaire