I just had siding replaced and I have several exterior lights that need to be put up. The old lights had no junction box, there was just a hole cut into the siding and plywood for the electrical, and the lights were mounted directly to the siding.

When they re-did the siding, they put in these vinyl blocks, so at least there is a solid surface to mount against.

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Problem is there is still no junction box to screw the fixture into.

Can I just screw directly into the vinyl block with wood screws? I don't see any other options, since I can't remove the block (it's nailed in underneath the siding).

  • Is there any slack in the cable? Can you get some of the outer sheath to the exterior?
    – bib
    Commented Feb 5, 2017 at 15:37
  • Not really much slack. There are two lights hanging on the garage and I have easy access to them from the outside, but there's one that's next to my front door and I have no easy access to the interior wall.
    – Brian
    Commented Feb 5, 2017 at 15:58
  • Not sure what you mean about getting some of the outer sheath to the exterior. You mean the sheathing around the cables?
    – Brian
    Commented Feb 5, 2017 at 15:58
  • You could attach a steel 'pancake box' to the vinyl with multiple screws and attach the fixture to that. Technically you are supposed to have the sheath of the cable inside the pancake box, but it isn't a perfect world. Alternatively, you could cut a 3 inch or 3.5 inch diameter hole (or whatever dia the round box requires) in the vinyl and insert a box that grips the vinyl. This might allow you to bring the cable into the box. Is there wood sheathing under the vinyl (OSB or plywood) or is there a stud to attach the box to? There are specialty boxes. Do you have a ground wire? Commented Feb 5, 2017 at 16:05
  • Okay. I'll go to home depot and look for a pancake box that I can insert into the block. I checked and, at least for the two outside the garage, I have plenty of slack I can pull through to get to the sheathing. There is plywood, then foam insulation, then the vinyl block. Yes I have a ground wire, it's just hidden inside that hole.
    – Brian
    Commented Feb 5, 2017 at 16:08

1 Answer 1


I realize this is a little late, but for those reading this for answers:

Make a 4” round hole in the center. The existing hole in the siding box is around 1-1/8”, so if you have a 1-1/8” hole saw, Nest it in the 4” to stabilize. If you want to save money and not buy a hole saw, trace your octagon box (keep reading) and use tin snips to cut out the hole.

Get yourself an octagon box that has a depth close to, but less than the depth of the siding box. Install an NM clamp (plastic or metal, plastic will work better). Space the box off the back of the box so it is flush to the front, screw it down, and install the light.

Tip: Screws can be your spacer. Make a triangle out of three screws that prevent the box from setting too far back. The secure the box with 2 screws.

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