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knob and tube in insulation

Posted by cfbuckley (My Page) on
Sat, Jan 26, 13 at 13:38

Hi All,

I am in the process of purchasing a 1927 bungalow in need of knob and tube replacement. I've got a pretty extensive understanding of the knob and tube replacement at this point but would like to get a better sense of what this means for my walls.

The home has knob and tube running through an insulated attic crawl space feeding down into 3/4 of the main floor (wiring in a kitchen and bathroom were updated during previous remodels). It has now become apparent cellulose insulation was blown into the knob and tube on the main floor at some point. All walls in impacted area are original lath and plaster.

I have received bids to remove all knob and tube/rewire and update mic. electrical and plan on doing so. But, I am unclear on how invasive this will be to the plaster and what sort of repairs and costs I'm looking at once everything on the electrical end is wrapped up. Contractor has said that while some clients will pay extra to fish and avoid getting into the walls it will be far less expensive for me to let them cut in and then repair the walls.

I'm already looking at swallowing the cost of this knob and tube job (or at least a large part of it - seller is offering some credit but not much) and want to be sure I'm not getting myself into real trouble - both financially and in terms of retaining the aesthetic integrity of the home.

Any and all info/suggestions/thoughts on what this job means looking through the wall damage filter would be very helpful. Thank you!


Follow-Up Postings:

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RE: knob and tube in insulation

K&T is NOT allowed to be buried in any insulation.

It depends on free air for both voltage isolation and power dissipation.


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RE: knob and tube in insulation

Thanks for the response Brickeyee - We are in total agreement and there is no question that I will be replacing the k&t before I move in. My concern at this point is more evaluating the merits and costs of going in through the walls and repairing that plaster v. paying to have them fish it in best they can w/the understanding that fishing will be made difficult by the existing insulation that was blown in.


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RE: knob and tube in insulation

It is not usually that hard to fish through cellulose.

A typical flex bit goes through like almost nothing is there.

Sometimes you can even push fiberglass rods through.

" insulated attic crawl space feeding down into 3/4 of the main floor "

If it is a a large enough area to work in you have to balance labor hours of fishing against repairing plaster.

The problem in many areas is that plaster repair is pretty much a dead art.

What lathe is behind the plaster?

Wood or expanded metal?

Wood is often easier to cut into and then repair.

1927 is a little early for gypsum backing (2 coat instead of 3 coat plaster).


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RE: knob and tube in insulation

That's really valuable info for me, Brickeeye; thank you.


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RE: knob and tube in insulation

Just get some estimates from a plasterer if you can find one. I've had two at my home recently. They told me that within reason, the number of areas to be repaired don't change the cost too much. They have to make several trips and set up and clean up each time so what they do in between might end up being pretty trivial. Have you got cracks in some places to fix or some rough areas?

Your electrical contractor might be assuming that your repair will be a hack job rather than a quality plaster repair job. Get an idea from him what kind of cutting he would want to do and convey that to the plasterers. Put tape on the walls to mark the anticipated damage if that makes it easier.

You mentioned removal of K&T. My understanding is that it can be disconnected and stay in place when modern, new conductors are installed.


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