Romex wiring between ridgid foam

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JasonS
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Romex wiring between ridgid foam

Post by JasonS » Tue May 16, 2017 1:04 pm

Hi I have a ceiling with no lights in it and I would like to add some. I can't get into the addict cause it's a sloped roof. I want to accomplish 2 things better insulate the ceiling and run new track lights in this room. My thought is if it is legal I would run the wiring over the existing drywall stapling it through the drywall into the truss. Then put 2" ridgid foam over the entire ceiling and over the wiring. The drywall over top of the foam board and mud tape paint add lights done. It this allowed in the code?

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Aaron
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Re: Romex wiring between ridgid foam

Post by Aaron » Tue May 16, 2017 4:59 pm

You could do what you're planning with either EMT (non-flexible tubing) or Type MC (flexible metal-clad cable) with steel boxes and covers. This is for protection of nail/screw punctures.

Either choice is also acceptable for surface mount, as well. You're right that NM (non-metallic cable) can only be behind drywall.

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emtnut
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Re: Romex wiring between ridgid foam

Post by emtnut » Wed May 17, 2017 1:32 pm

If I'm understanding your set-up .... I don't see a problem as long as you have the 1 1/4" clearance, which you should with the 2" foam.

I've never come across that before ... The main worry I would have is you basically have 2 vapor barriers now, and the inside layer of drywall will be subject to mold ?

Maybe Shannon or Sprucy will comment on that.
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emtnut
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Re: Romex wiring between ridgid foam

Post by emtnut » Wed May 17, 2017 4:07 pm

I was talking with Aaron on this ... Even if you glue the foam board on the existing drywall, you would need at least a 3" screw to attach the drywall.So a no-go as far as code.

EMT or MC cable 'could' work ... but I still think you'll have a mold problem brewing !
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Shannon
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Re: Romex wiring between ridgid foam

Post by Shannon » Wed May 17, 2017 10:52 pm

If there is an existing poly vapour barrier under the drywall already then you are likely asking for a mold problem. You could remove the existing drywall and vapour barrier and run the wires then add foam and drywall over that.
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Aaron
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Re: Romex wiring between ridgid foam

Post by Aaron » Thu May 18, 2017 2:52 pm

That's what I'd recommend. The demo is a pain, but a job done right is a source of pride. You can then use NM cable. Or you could go with batts and a poly vapor barrier instead of the foam.

JasonS
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Re: Romex wiring between ridgid foam

Post by JasonS » Fri Jun 09, 2017 8:32 am

Ok thanks for the great Info guys

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A. Spruce
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Re: Romex wiring between ridgid foam

Post by A. Spruce » Fri Jun 09, 2017 9:04 am

Shannon wrote:You could remove the existing drywall and vapour barrier and run the wires then add foam and drywall over that.
Yep, this is the route I'd go as well. While the drywall is down, you can run all the wires you like AND upgrade your insulation before the new drywall goes up. 8-)

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