DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Electrical (
-   -   Knob & Tube -- Cellulose Insulation (

rlowe82 10-28-2011 03:46 PM

Knob & Tube -- Cellulose Insulation

I did a search but didn't find anything specific to my issue.

I am in Los Angeles in a house that was built in 1921. It has knob and tube and is still running electricity that way. We've had a licensed electrician come and inspect all the wires and breaker box and retrofit all the plugs to be grounded. We asked him if cellulose could be blown in over the knob and tube in the attic and he said that'd be fine because the wires are still in good shape.

I called an insulation company with experience in knob and tube and they said it's fine, as well. Especially because cellulose is non-flammeable.

I still have reservations, though. Despite both the electrician and insulation company saying it's safe, I'm worried. A lot of forums say to replace the knob and tube completely.

Should I be? Has anyone else blown in cellulose over knob and tube?

We are planning on only blowing in the cellulose in the attic, not the walls.

Thank you!

jarleifvaagen 10-28-2011 03:58 PM

As a Home Inspector in Michigan I've seen knob and tube both buried, and exposed... It IS a fire hazard especially when buried in insulation...

try this approach.. call the insurance company where you have your Home owners policy, tell them you have knob and tube wiring that's buried in cellulose insulation..and ask them for a discount.. I don't think you'll find the outcome desirable if you like your current insurance company..

just my 2 cents.


Techy 10-28-2011 04:06 PM


Originally Posted by rlowe82 (Post 758840)

and retrofit all the plugs to be grounded.

I'm interested on how this was done, K&T does not carry a ground.

rlowe82 10-28-2011 04:23 PM

I feel like I'm going around in circles.

My insurance company says it's fine to add cellulose over knob & tube as long as we have a breaker box.

As for the ground, I don't know the specifics but I do know our electrician added GFCI outlets to the kitchen and bathrooms and a grounding rod. Can the ground be added off the neutral wire? (sorry, I don't know anything about electrical systems but I am going to call my electrician.)

jarleifvaagen 10-28-2011 04:37 PM

gfci protectionwhere no ground wire is present is okay per the electrical code, but in my own mind no substitute for a ground wire at each receptacle.. and by the way your insurance company is nuts, but that is no longer your problem, as you have done your due diligence. make sure you have enough insurance in case it burns down.

McSteve 10-28-2011 04:40 PM

The thing that would bother me about insulation around K&T is only partially that the insulation might be flammable; it's also that K&T wiring is rated for 15A in free air. Covered in insulation, the wiring can't dissipate heat as effectively, and could possibly overheat. I could swear I saw something in the NEC about K&T and insulation, but I can't remember what or where.

Edit: But Speedy Petey does :)

Speedy Petey 10-28-2011 04:40 PM

DO NOT add insulation on, in or around K&T wiring!!!

394.12 Uses Not Permitted.

Concealed knob-and-tube wiring shall not be used in the following:

(1) Commercial garages
(2) Theaters and similar locations
(3) Motion picture studios
(4) Hazardous (classified) locations
(5) Hollow spaces of walls, ceilings, and attics where such spaces are insulated by loose, rolled, or foamed-in-place insulating material that envelops the conductors

NEC commentary on this section:

Concealed knob-and-tube wiring is designed for use in hollow spaces of walls, ceilings, and attics and utilizes the free air in such spaces for heat dissipation. Weatherization of hollow spaces by blown-in, foamed-in, or rolled insulation prevents the dissipation of heat into the free air space, resulting in higher conductor temperature, which could cause insulation breakdown and possible ignition of the insulation.

This is nothing new! Whoever told you this was fine had no clue what they were talking about.

Speedy Petey 10-28-2011 04:43 PM


Originally Posted by rlowe82 (Post 758866)

As for the ground, I don't know the specifics but I do know our electrician added GFCI outlets to the kitchen and bathrooms and a grounding rod. Can the ground be added off the neutral wire? (sorry, I don't know anything about electrical systems but I am going to call my electrician.)

GFI protection is a safe alternative for 3-prong receptacle retrofits. It does NOT provide a ground though.

A ground rod DOES NOT AT ALL provide a ground in a sense of the safety ground in a receptacle.
Hopefully he did not simply sink a ground rod and connect to that.

rlowe82 10-28-2011 04:52 PM

Thanks so much, everyone.

So both my electrician and insulation company are pulling a fast one? Ugh. This sucks.

Speedy Pete -- thanks for your info. I found this on Wikipedia, but don't know where to look to verify it (since I don't believe everything I find on Wikipedia). Can you?
However, California and Washington, as well as possibly other states, have actually reversed the ruling on insulation around K&T. They did not find a single fire that was attributed to K&T, and permit insulation provided the home first passes inspection by an electrician.[9][10]
I looked at our home inspection report and there's actually a combination of Romex and knob & tube. Could this explain the grounding? I am getting more confused by the minute! I need to have my electrician explain everything to me.

AllanJ 10-28-2011 04:59 PM

Any 2 wire circuit can be retrofitted with a ground wire, which runs from the various receptacles and down to the panel following exactly, approximately, or vaguely the route of the circuit conductors.

A retrofitted ground wire from an outlet box fed by knob and tube wiring may not be "grounded" at a nearby outlet box that had a ground such as in a Romex cable feeding it.

If the retrofitted ground wire first reached a ground rod connected by a fat ground wire (grounding electrode conductor) to the panel it may be clamped on there (or to said fat ground wire).

Just my interpretation of the National Electric Code: A retrofitted ground wire can daisy chain among several outlet boxes on the same circuit and then go down to the panel.

rlowe82 10-31-2011 02:43 PM

Thanks, everyone!

So what kind of insulation is recommended with knob & tube?

joed 10-31-2011 02:49 PM

No insulation is recommended. It need to be free air for cooling.

jimmy21 10-31-2011 03:25 PM

39 Attachment(s)
knob and tube is usually pretty darn safe, if left alone. Start messing with it and it becomes incredibly unsafe. The system has lasted this long because it probably hasn't been touched. Adding insulation is doing something that the system just wasn't designed for.

rlowe82 11-03-2011 11:48 AM

Hi everyone,

This thread has been really helpful.

I spoke to an electrician who said he could replace the knob & tube that is in the attic to Romex so that it would be safe to have cellulose insulation around it. His process would be to take the knob & tube that runs up and inside the walls and add a junction box, where he would then change out the existing wiring and add the Romex. The Romex would run throughout the attic, which he said is far safer to cover in cellulose.

Any thoughts? Does this seem like a solution? He said that it would be a huge job to replace ALL of the knob & tube, including the wiring that runs in the walls and through the lathe & plaster, so this would be a good way to ensure safety while still having insulation.

Please let me know!!! Thank you much in advanced.

McSteve 11-03-2011 11:56 AM

Once all the K&T wiring in the attic is replaced with Romex, it will be perfectly safe to insulate the attic.

All times are GMT -5. The time now is 09:21 AM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1