Spray-foam air sealing failure at 15 years?
I’m in 6a (Minneapolis) in a hundred year old two story house. We had air sealing and blown in cellulose done in the walls and attic in the Obama-incentive-era time- basically 15 years ago. Fast forward to last year and I discovered in a bathroom renovation that we still have some stray knob and tube wiring. There is no visible knob and tube anywhere -but I’ve now done a lot of pulling outlets out and have found that what now remains is a portion of a circuit on the second floor that is buried under cellulose and fiberglass and feeds wall receptacles across 3 different rooms almost the entire length of the house. All the overhead lights on the circuit appear to be updated. Because only a portion of the circuit is old I’m trying to find a box where the new and old come together (so I can de-energize the old) and it means I’m digging and poking in the attic A Lot. The knob and tube was under the fiber glass so I’m slightly less irritated at the contractor who did the insulation and didn’t report the knob and tube , but every light box I’ve poked into so far has updated wiring and was air sealed with spray foam – and the spray foam has fallen out. So I’m only discovering this because I’m digging around. So two questions- what should I do differently so that air sealing this time around doesn’t fail in 15 years- and any advice on finding where the knob and tube is tied into the new wiring? I’m following the new wire from the panel and so far its gone from basement to the attic to the far end of the house without hitting a box. Thanks!
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Do you have a live outlet that is on knob and tube? You can get circuit tracers where you plug one device into the outlet and then the other device gives an audible signal when it's near the wire. That allows you to trace the circuit. If you only have a light you can use a bulb to outlet adapter.
The tool you want is called a "circuit breaker finder."
Thanks DCcontrarian, I've used a circuit breaker finder but not a tracer.
Sadly, if someone wants to hide knob and tube wiring it can be very hard to detected short of opening the walls and looking.
You may want to look at the Walabot it sees thru walls! The video is amazing. I think you could differentiate Romex from knob and tube because Romex may display as one object and the N&T should be separated enough that they will show a 2 objects.
https://www.youtube.com/watch?v=WQK_4duKwi0
Walta
Are you sure that knob and tube wiring is actually in use? When K&T is replaced the old wires aren't always pulled out. At the same time, I've found a whole new panel where the romex went just far enough to not be seen where it was then connected to old K&T! So, yeah...a little more investigation and testing is needed.
A non contact tester will tell you if the wire is hot. You can use one of the receptacle testers to see if you have a ground or not. K&T doesn't, but sometimes a shady electrician will make a "bootleg ground" to fool the tester. You'll see a short wire connecting the neutral to the ground. If you find this, remove it. It's a dangerous method as the neutral is hot and can energize other grounded objects.
Yes, you're right there is knob and tube that is de-energized in the house, but this knob and tube is energized. My NCVT lights up and dings and the receptacles in the wall have the tell-tale slightly heavier wires covered in the snakeskin insulation. Most of the house has been updated- there are a lot of new wires. I've finally de-energized the circuit I first discovered the issue on. It included some lovely gems like new wiring spliced with knob and tube 6 inches *behind* the junction box. So in the junction box, the wires all LOOKED new and grounded, but I knew this circuit was mostly knob and tube so I pulled the box. An outlet tester is how I know the 5 outlets are ungrounded, and when I open them up they have heavier wires (and no ground). Its just a slow process of digging up the insulation and sliding plywood around and crawling around trying to find where these wires are going. Since I know there's new wires in the attic I thought it'd be easiest to tie into the new wires but I'm now several hours in and I've yet to find the box where the old and new are connected. I guess the only good news is that I haven't seen a bootleg ground!
hmm.... if the walabot could help me see thru walls and insulation that would be awesome!
Have you personally used the Walabot? They advertise heavily on YouTube and it seems too good to be true.
I've faced similar challenges in my old house- buried knob and tube, open splices, open AND buried splices, dangling non-wire-nutted hots, ungrounded boxes, shared neutrals, under-rated wires, bare exposed copper from pulling damage.....and on. Shocking stuff. (had to :)
It's still a work in progress, but I basically have had to map out everything and open every box, In my case, diligent continuity testing/iterations helped to narrow in on suspect areas. If it's new wire connected to old I would guess (and hope) that it's not buried in a wall. It should be in a box or under insulation in the attic, hopefully in a JB.
I like the idea of the tracer or walabot as mentioned in earlier posts, I have not used either one- would be great to know how it works for you if you go this route.
Good luck!
Thanks steve41, that sounds a lot like my experience. happily I haven't yet had any literal shocks though it does seem like there's definitely been luck on my side. And I'm now learning about Multi branch circuits since the new wires for this circuit are a 14-3 cable that is shared across circuits number 21 and 29 - clearly not an appropriate double pole breaker. I will perservere, and I do appreciate hearing stories from others slogging through the same bog!
FYI the 14-3 multi branch circuits would not be code compliant under most modern codes as they tend to require arc and ground fault breakers for almost every breaker.
Note you can greatly improve the safety of ungrounded/ K&N circuits by feeding them from ground fault breakers.
I have not personally used a Walabot but this is a quote from an actual user”
We have a couple of them at work, for doing cabinet installs. (Had a few too many 'oops' moments from the installers before.) They're... ok. Kinda fiddly to set up and use, but they do work. At least, we haven't had anyone put a screw into a drain pipe or water line since.”
Walta