Siding Outlet Boxes

[Rossn]

I have cedar shiplap siding with a 3/4" vented cavity between it and the sheathing. There is no practical way for water to get behind the siding.

In this situation, is it NEC 2017 compliant to use a Carlon old work box as an outlet box for a step light and a standard pancake pan for the sconces next to the door, provided the outlet boxes are flush with the siding?

Code references appreciated, if available.

 

[wwhitney]

I have cedar shiplap siding with a 3/4" vented cavity between it and the sheathing.

And presumably a weather resistive barrier between the 3/4" thick strapping and the sheathing.

There is no practical way for water to get behind the siding.

Obviously not true, siding sheds bulk water but water will penetrate it, which is one reason to use the rain screen cavity behind it.

In this situation, is it NEC 2017 compliant to use a Carlon old work box as an outlet box for a step light and a standard pancake pan for the sconces next to the door, provided the outlet boxes are flush with the siding?

Based on the above comments, I'm going to say those are wet locations, so a listed wet location box is required, per NEC 314.15.

Cheers, Wayne

 

[Sponsor]

 

[Rossn]

Thanks, Wayne. The siding is R5 Zip, so no additional layers other than 3/4" furring strips and one area with 1/4" furring.

We are doing wood rings of furring around the receptacles (behind the siding), which are a recessed weather resistant box. Issue comes with the step lights, which are all into the 1/4" furring.

Given the shiplap and window design, some moisture, generally vapor, is likely in the rainscreen, but true water would require a hose or pressure washer spraying it. Even that would have to hit just the right spot. My sense on the rainscreen is more about drying moisture in the wood (keep in mind shiplap install).

I was reading a trade joural article earlier (can't find again) which was indicating it is a bit of a gray area of the code, but often accepted if it does not penetrate the siding it is considered dry. It does not discuss rain screens, however I also think of siding without a proper rainscreen, and often not less likely to have moisture behind it. The gist of the article was that the code's intent is trying to protect the home from unseen water damage.

Where I mount exterior sconces, if I use a pancake, then only NM would penetrate the sheathing, not the box, so I think an inspector may permit that.

I'll try to work in a water tight box, but it will be difficult to seal to the sheathing after the fact, and I wouldn't be able to mount it as intended (back of box will be into the foam layer).

 

[wwhitney]

Issue comes with the step lights, which are all into the 1/4" furring.

Do you have a detail drawing for that condition?

Given the shiplap and window design, some moisture, generally vapor, is likely in the rainscreen, but true water would require a hose or pressure washer spraying it.

That may be 99% or 100% true in the field (and the difference in that matters for this discussion), but the joints around siding penetrations (such as these boxes, or window frames) will likely allow water in. Even if caulked, unless you have a rigorous program of replacing the caulk every year or two. One of the benefits of a rainscreen construction, in my mind, is that you don't need to caulk those joints, you have a drainable region behind.

Where I mount exterior sconces, if I use a pancake, then only NM would penetrate the sheathing, not the box, so I think an inspector may permit that.

I agree that if the box is mounted to the sheathing, NM cable can penetrate the sheathing and enter the back of the box. Is a standard 1-1/2" deep outdoor round box too deep for your sconces?

https://www.hubbell.com/bell/en/Pro...door/Boxes-Covers-Plates/PRB57550GY/p/1670472

If the shiplap has a flat face, is 3/4" thick, and mounted on your 3/4" thick furring, that should work great for a sconce. If the face of the siding isn't flat, I would suggest a cedar mounting block of the correct thickness that the siding can butt into.

Cheers, Wayne

 

[Rossn]

I can likely go up to 1-1/2" thick on the sconces... they are all in the 3/4" furring section. The siding is closer to 11/16", but it may work out OK. I have not precision located the sconces yet, as the electrical phase is just starting and was going to see how they shine once the siding is up.

I was looking at some of those boxes you linked; issue being the 'mounting ears', given the siding will already be up. I would have to poke around and see if it is permissible to mount them by screwing through the backs of them, which I think the NEC generally prohibits if not approved by mfg, but that is going off a vague memory. Any idea on that?

This drawings give an idea of the 3/4" furred section... 1/4" is actually closer to 5mm (Luan board).

 

[wwhitney]

I was looking at some of those boxes you linked; issue being the 'mounting ears', given the siding will already be up.

Yes, with that style of box it would be desirable to locate and install the electrical boxes before (or as) siding, Not clear on why that would be a problem. Internal mounting screws in a non-metallic box are only allowed if the box is designed to keep the wiring away from the screws (typically the screw locations are recessed).

But I think you could use a metal 4" round x 1-1/2" deep weatherproof box and I think mount it with screws in the back of the box (with some silicone in the screw hole/box penetration); the metal box would need to be bonded to the EGC, so the metal screw would end up bonded.

On the detail drawing, I was specifically asking about the step lights and the 1/4" furring; or a link to the step light itself, along with a description of where its face ends up relative to the face of the siding, might suffice.

Cheers, Wayne

 

[Rossn]

Yes, with that style of box it would be desirable to locate and install the electrical boxes before (or as) siding, Not clear on why that would be a problem. Internal mounting screws in a non-metallic box are only allowed if the box is designed to keep the wiring away from the screws (typically the screw locations are recessed).

For one, lots of balls in the air right now! Regardless, siding is already up in the locations that would take sconces, and so it's too late for that approach. When I talked with a master electrician at his light shop, he suggested just using the pancakes, and at that point I stopped worrying about finding optimal placement (there are some complexities with shining into eyes as people walk up steps, below), but he was probably unaware of the rain screen.

I agree, I doubt the inspector will give me too hard of a time about that. Most of the exterior light fixtures I have seen are mounted like garbage, and unstable, so I think they may give some leeway on screwing through the back of the box.

Edit: Nope, don't have a drawing of the 1/4" section with step light... something I'll have to improvise and figure how to mount a metal exterior box flush with the siding, while penetrating somewhat into the foam layer.

 

[wwhitney]

Maybe my interpretation is too strict and you could argue it's a damp location.

As a practical matter, if you just have a single NM cable (12/2 or 14/2) stubbed out at each location, and there is some volume in the canopy of the light fixture, you could use a PVC 4" round pancake box that is 5/8" deep, and just silicone any unused holes. It has a recessed boss for a mounting screw in the back, so you should be able to just hole saw a 4" hole in your siding. And mount it over a 4" disc of material to bring the face flush with your siding, if that's what you need.

https://www.homedepot.com/p/Carlon-...Ceiling-Fan-Box-Case-of-18-B708-SHK/202199751

Cheers, Wayne

 

[Rossn]

Thanks - I had seen those. I can't figure out why they don't make a plastic remodel pancake box that is water tight... seems like those would see a lot of use. I do think the inspector would consider those damp, not wet. There is a 30" overhang above these areas, and no opening in the siding except the top 3/16". When I asked about soffit lights, they called it damp. Beneath a window, I can see being called wet.

2017 NEC 314.23(B)(1) leads me to believe screwing through the back of a grounded metal box and sealing the screw is acceptable. It also sounds like screwing through a metal box is less suspect than through a PVC/Plastic box (not allowed), due to the screw inherently being grounded with a metal box. (314.43)

314.23(B)(1)