Knob and Tube Replacement

[Sean McDermott]

Can anyone provide their experience with replacing knob and tube wiring? I'm looking into insulating the exterior walls of a 1925 house with foam insulation and would like to replace the old knob and tube with romex prior to doing so. Of course I'd like to minimize any disturbance to the plaster walls. Any insight, cost projections, funny stories, etc. would be helpful.

[Joe Ott]

Sean,

If done correctly (meaning done to code by a certified electrician), expect to spend a lot of money. Not only will you have to remove/replace all the K&T (knob & tube), you likely will have to upgrade your service panel which is probably only 60 or 80 amp. Too low for today's requirements. This is really a job for a certified electrician. Not a weekend job based on what the guy at home depot is telling you...

K&T, although good in its day, can be dangerous stuff. It was designed to be in the walls within open space. The air space in the walls provide heat dissipation. Most often it was only #14 wire too. In addition, the fabric insulation on the wires is likely deteriorated and can be bare in many places. The wire itself could have lots of oxidization reducing its load carrying abilities resulting in easier overheating. Also, over the years, well meaning do it yourselfers have probably hacked into it creating other hazards.

Another thing about K&T is when the house was built, the runs were usually not logical. They would run what was convenient at the moment and would often splice in here and there to run a circuit elsewhere. It can be a real spiders web as to where each wire is really going and what room, or rooms, it is providing power to.

Think about what can happen if insulation is blown in over those old wires and somebody pops in a 30 amp fuse in place of a 20 amp fuse (or breaker) because it keeps popping. Then you plug a microwave in and a space heater (not realizing it's the same circuit). It will over heat.

The insulation guys will often say it is ok to blow in insulation over K&T. Don't believe them for the reasons above. Ask your insurance company if they will still cover you. You might also ask your insurance company if they will still cover you if you rewire yourself and not have it inspected. Just things to think about.

Lastly, consider that our old houses were built to breath. If you button your house up tight with insulation and so-called efficient windows, it can no longer breath. This can lead to lots of other problems. Such as moisture build up, radon gas build up, mold, mildew and so on. This can also have an affect on your HVAC systems. Newly constructed housing that are efficient have all this in consideration. Even HVAC. It all has to be considered as one big system.

Right now if a storm blows through and you get some water between a wall, you probably will never know because it will be able to dry. With insulation blown in it likely will not dry as quickly and can start to cause decay in the surrounding wood.

If it were me, I would do the electrical first. Have it done right. If done right, to code, and inspected, check with your insurance company, you might get a break.

I know, a lot of people will tell you they had it done and blown in over K&T and never had a problem. But, it's your house and family. Don't take a chance.

Do you want to know my thoughts on vinyl replacement windows? Ha! Don't ask.

Just my thoughts and opinions. Your mileage may vary...

[Ruth Sholtis-Furyes]

I am doing what you are planning Sean. I will let you know costs/etc once I know them too. I am having it professionally done. We were going to do it ourselves but just don't have the time. We are also upgrading the panel to 200Amp. Only b/c future improvements include a hot tub, kiln, plasma cutter.

I am wondering about foam vs. cellulose. Read a lot on the web and everyone contradicts everyone else. I am leaning toward foam at this point. This Old House prefers foam. The book I am reading on "greening your home" says foam.

I will not be replacing the windows, nor will I be doing siding. That's just wrong.

[Bryan Schwegler]

I am wondering about foam vs. cellulose. Read a lot on the web and everyone contradicts everyone else. I am leaning toward foam at this point. This Old House prefers foam. The book I am reading on "greening your home" says foam.

I will not be replacing the windows, nor will I be doing siding. That's just wrong.

Ruth,
We had foam blown in our house by USA Insulation, I'd highly recommend them, they did a great job.

All my research said foam is definitely the better option of the two.