I’m planning on blowing in cellulose in my 1922 built duplex which has balloon framing, any suggestions? What’s the verdict on “knob & tube” wiring in the stud cavities and the blown in cellulose?
Edited 5/13/2002 1:47:11 PM ET by POPEYE87
I’m planning on blowing in cellulose in my 1922 built duplex which has balloon framing, any suggestions? What’s the verdict on “knob & tube” wiring in the stud cavities and the blown in cellulose?
This deconstruction program leader oversees the collection and reuse of a variety of products and materials.
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Replies
A couple issues:
The cellulose would be in direct contact with the wires, which get hot, and hold in the heat.
The cellulose conceals electrically hot wires, so if you go digging around in it with your hands, you could make contact with a wire.
-- J.S.
K&T if properly installed (and not added onto incorrectly) can be a safe wiring method, if you don't mind adding equipment grounds where you need 'em .
With the cellulose packed in tight, the heat buildup around the wires could be a hazard. This is more of an issue for heavily-loaded circuits, of course. I've seen photographs of an instance where a stud was charred by the heat radiated from a K&T wire buried in insulation. Granted there was probably an 1800 watt space heater on the circuit--but an overload or high impedance short circuit can happen anywhere and heat up the wires before a breaker opens.
Your safest bet would be to re-wire before insulating. I suggest this because it'll be a real gripe afterward.
I'd strongly recommend rewiring if the circuits are protected by circuit breakers, which allow considerable overcurrent (= heat in the wires) before opening. Even if you'remanaging to getby on the existing K&T, it's probably just adequate. If at all possible, now's the time to upgrade.
If the house still has a fusebox, protect all the branch circuits at 15 amps. And hope for the best.
Cliff
Knob and tube (K&T) wiring was not designed to work in contact with thermal insulation of any type. The insulation contractors that I have worked with will not install insulation in any space that contains K&T. I have been told that no reputable insulation contractor will. The consequences of doing so could get ugly.
Given the age of the wiring is likely that the electrical insulation on the conductors in the K&T system has broken down and may have fallen off. Don't worry too much about this as K&T was designed to remain relatively safe without insulation on the individual conductors. If not tampered with or abused K&T can be a very durable system. How many things in this world can be counted on to still be working after 80 years.
Not only would you be in danger of burning down your house but you might end up killing or injuring any person who might have to feel their way through the insulation. If someone was in contact with a grounded surface, air ducts or pipes, and then accidentally contact a live conductor in the K&T system they could be electrocuted.
Don't insulate around K&T wiring. If you must add thermal, as opposed to electrical, insulation have the K&T replaced. If you choose to skip the insulation it would be a good idea to have someone familiar with K&T inspect it. Many electricians have little or no experience with K&T so ask around for contractors who are old timers or do a lot of work on older homes. Consider rewiring the house.
.
To emphasize what others have told you: it's dangerous. The NEC doesn't allow it.
In my area, many electricians say "No big deal, we see it all of the time." The fire marshalls say "It is a big deal, it causes many fires." I know who I'd listen to.
Thanks for the reply one and all!
I had a feeling that it was an unsafe practice, but needed to get some feedback.
Now, How do I go about finding which stud cavaties have the K&T in them?
If you are gonna replace the wiring then you don't have to care where the existing wires are.
Run the new romex where it is best for you to do so (access, logical routing, and so on) and kill the old wires (you probably won't be able to pull them out if they are routed thru any studs along the way, but total removal is best to prevent future confusion).
For wires that could not be removed from the wall, mark them as "abandoned" and wire nut the two ends together to short them out. Be sure to do this on both ends of that abandoned wire and this second step assures that no one can ever find the wires in the future and foolishly try and use them for anything.
Now, on the other hand, if you are thinking about just insulating around the existing wires I would recommend against trying that for two reasons:
1) you leave gaps in your envelope which will reduce the effectiveness of your insulation (like leaving the window open).
2) the wires don't usually just go up or down one stud bay, they wrap around the walls and daisy chain outlets and fixtures all over the place. You can never be sure you kept the insulation away from them. To repeat the excellent advice above, do NOT bury K&T in any insulation.
There are lots of good reasons for saving and maintaining old world stuff (woodwork, plaster, windows, doors, cabinets, hardware) but there is not good reason for hanging on to out of date electrical supply. Replace it now, before you insulate (while it is much easier to do it, when the bays are still 'empty').
By the way, if you are trying to get wiring to places that are behind good plaster, etc and you can't figure out how to get there, call a pro, they have tools and techniques for getting wiring runs into places that you could not even imagine possible. I have learned some, but it is a steep learing curve on your own.
If you can't afford to hire the whole thing out, and am pretty handy/clever/good learner and humble, hire a pro who will be willing to work with you for the first few, and learn as much as you can and develop a relationship with that person to give pointers when you're on your own.
:o)
Some of the fancier stud finders from Zircom have a function to find live wires. They work fine for Romex, and should also find the hot side of your K&T, provided it's hot at the time, so turn the switches on. Another possibility with K&T is that sometimes they ran the hot and neutral very far apart, like one thru the attic and the other thru the basement. Subsequent modifications may have been done in black pipe or conduit, and these won't show up on the electrical search, though the metal function will probably find them. Alas, the one thing that stud finders don't do in old lath & plaster houses is find studs.
As noted, you really don't need to find and remove/replace the K&T. You can run your new stuff elsewhere. But if it's convenient, why not pull it out and enlarge the holes in the framing to accept Romex? (Also, if you can get the old ceramic stuff out in good condition, there are collectors who'll buy it from you.)
-- J.S.
Edited 5/14/2002 3:22:58 PM ET by JOHN_SPRUNG