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I want to mount a porch light on my outdoor shed/office. I recently had an electrician place interior wiring however I elected to do the fixtures myself.

Uh oh.

Here's what the back of the porch light area looks like (on the inside of the shed):

back interior

Here's what the front looks like:

front exterior

Here's a picture of the light I want to put on the outside:

beacon light

The wall is a solid piece of wood about 1.5 inches thick so I don't think there's room to add a fixture bracket.

So... I'm stumped. How should I attach the light?

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  • I may be missing something (like, say, IQ), but I can't figure out Your problem. You got wires in place, You got a hole. Are dimensions a problem? Or, maybe, You are in doubt about the mounting? I guess I need more info. Without dimensions and other details I'm blind here. – Marek Oleszczuk Jul 30 '15 at 6:39
  • Historically when I've mounted light fixtures in the past, there's been a metal box in the wall that I've attached to. In this case, the box doesn't exist. So my question was regard specifically how to attach the fixture to the wall in the absence of that, given the fact that I can't bury a metal box in the wall. – Mike B Jul 30 '15 at 13:44
  • Ok then, so fixtures, by default, got something to fix them by to the surface. Be it metal 'casings' or just a sheet of metal. If Your fixture is missing that, so tha't the problem. Well, I guess that folks just made correct answers anyway. – Marek Oleszczuk Jul 31 '15 at 6:29
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A pretty common approach is to build a small platform for the lamp to sit on, something like this

extlamp

This has the advantage of giving you more depth to mount a receptacle box. You can use 3/4 inch material (nominally 1x ) or larger, such as 5/4 stock. You can then cut a hole, using a hole saw through the new block and the siding underneath giving you enough depth for a much deeper box, like this one

plastic round box

It also has the advantage of making it easier to get the base of the lamp vertical.

After the box is set, I would caulk the entry point of the wire and around the box itself. After the lamp is mounted, unless the fixture has its own gasket, caulk around the top, sides and all but a small section of the bottom (a weep hole just incase any moisture gets in.)

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  • Have you ever looked inside one of those "platforms"? I'd be surprised if there was a box in there, unless the box was built into the wall (like it's supposed to be). – Tester101 Jul 30 '15 at 17:48
  • @Tester101 I had them build the platform and cut the hole. I put the box in before I wired up the fixture. – bib Jul 30 '15 at 18:13
  • Then your case is unique. Most of those things are put on the the siding company, and are purely cosmetic. – Tester101 Jul 30 '15 at 19:05
  • @Tester101 Cedar clapboard, a cedar block, serious craftsman carpenters (and a builder who is a personal friend) working to match the existing 1869 (with a 1905 reno) farmhouse. They done good. – bib Jul 30 '15 at 20:51
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I would opt to use a 1/2 pancake box 4" in diameter. The NEC code does not permit the canopy or empty space of a fixture to substitute for cubic wire space for wires larger than #16 gauge. And a 4" pancake boxes cubic space legally can only hold one 14/2.

pancake box

Since you already have the wire conduit on the inside of the house I would also consider using something like this box to mount the fixture to. round weather proof box

After reading a lot of the great comments I wanted to update my answer with some new advice. 1/2" Round Extension Ring

Because a 4" pancake box is limited on the cubic depth you would need a round extension. 1/2" will add an additional 3.3 cubic inches. A 3/4 extension would add an additional 5.0 cubic inches One 12/2 would require 6.75 cubic inches so a 1/2" extension would suffice.

Installing the pancake box and the 1/2" plaster ring would require 1" of depth so that leaves you only 1/2" of wood to mount the box to. Using three or four weather rated 1/4" wood screws would secure the box without penetrating the interior side.

As a side thought maybe you could only recessed the pancake box 1/2" and leave the plaster ring concealed behind the light box. From the picture it appears to have enough room to conceal the extension ring.

Keep in mind you will probably need to rotate the box so the mounting bracket that comes with the light will not interfere with the box or the extension rings screw holes.

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  • is that box rated for wet or damp locations? – Tester101 Jul 30 '15 at 13:41
  • Thanks. I'm pretty sure that the wire is 12 gauge (but will confirm). Does that mean that I probably can't use the pancake box? – Mike B Jul 30 '15 at 13:47
  • You may not be able to make your connections in that box, even if you were using #14.. See Example No.5 in this article. – Tester101 Jul 30 '15 at 13:59
  • #12 wire negates this whole argument, but for clarity's sake, the Example No.5 @Tester101 provided assumes a factory installed internal cable clamp. Otherwise, the 7 cu. in. capacity would squeak by, although I personally have a strong dislike for pancake boxes. – mjohns Jul 30 '15 at 19:17
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    A sharp chisel. – Kris Jul 31 '15 at 14:17
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Not sure if it's the "approved" method, but I've seen it quite a few times (mostly for fixtures on the front of a garage). The fixture wires are fed through the hole into the box inside, where the electrical connections are made by approved means. Then the fixture is simply mounted directly to the wall, typically with a gasket between the fixture base and the wall (should be included with the fixture).

You might use a bit of duct seal or similar, to seal the hole where the wires pass through. The gasket should keep weather out, but the duct seal will help keep the bugs out.

The "proper" method, with a normal wall, is to build an appropriately sized box into the wall.

Cross-section of wall

Then weather seal the fixture to the box.

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  • Thank you but to reiterate, I don't have cavity space in the wall for the box. That's what I'm struggling with. – Mike B Jul 31 '15 at 6:33
  • @MikeB What's the problem with passing the fixture wires through the hole, and making the connections in the box on the interior wall? – Tester101 Jul 31 '15 at 10:36

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