Installing vinyl siding around an obstruction. Siding Alterations:

Installing A Vinyl Siding J-Block
For An Outdoor Electrical Outlet

In This Article:

One panel of vinyl siding is lifted up, some nails are removed from the siding panel below, and a notch is cut in each piece of siding. A J-block is nailed to the wall and the siding is re-fastened.

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Skill Level: 3 (Intermediate) Time Taken: About An Hour

By , Editor


In the old days, whenever vinyl siding was installed around any type of obstruction (such as a light fixture, a dryer vent, or an electrical outlet) a "frame" of J-channel was placed around the object to conceal the cut edges of the siding. But this practice is tedious when there are lots of light fixtures or outlets to work around.

After many years of making vinyl siding, the manufacturers got wise and started selling a special component called a J-block that simplifies siding installation around common obstructions.

Vinyl siding J-Block for an outdoor outlet box. This is a basic J-block that I bought from Menard's for about $6.

Unfortunately, Menard's didn't stock this item in the green color of the siding. Since this was going on the back of the shed, I didn't care about the color not matching.


This J-block is a two-part unit. The top piece just pulls off.


Single-gang outdoor electrical junction box. This is a basic outdoor electrical box.


This junction box is supposed to be mounted using these two metal tabs that screw into the back. Mounting tabs for outdoor junction box.



With the mounting tabs, the box wouldn't fit inside the J-block.


So I drilled four holes in the back of the outdoor electrical box. These holes were just big enough to handle the mounting screws I planned on using. Drilling holes in back of outdoor electrical box.


Closer view.


Then I screwed a 3/8" cable clamp to the hole in the back side of the box.

When the clamp is fastened over the electrical cable, the screws will stick out pretty far. The red circle represents the large hole I will need to drill in the wall for this clamp to sit inside.

Cable clamp in back surface of outdoor electrical box.


I realized that the clamp would not fit inside the small hole that is pre-punched in the J-block, so I marked a larger hole to cut.


I cut out the hole with tin snips and end nippers.


This is the intended location of the electrical box.


Lifting Up The Vinyl Siding:

I slipped the vinyl siding removal tool (also called a J-hook) under the bottom lip of the siding panel and pulled the tool downward to release the siding.

Removing vinyl siding with siding removal J-tool.


Once the siding was lifted away at the end, I moved the tool to the right and pulled away the siding all the way to the far end.


On The Siding Panel Below:

I removed some of the nails so I could reach behind the siding.

I laid out a notch that was about ¼" bigger than the J-block. Then I used aviation snips to cut the notch in the siding.


I cut a similar notch in the upper panel of siding, but the vinyl cracked when I was cutting it. That's typical of vinyl siding... it cracks when the temperature is a little cool.


Cut out ready for the J-block.

With one-piece J-blocks, this project is much easier if the outlet straddles the joint between two siding panels.

Since my J-block has a detachable face, I could have easily put the cut-out in the middle of the siding panel. However, cutting the hole would have been trickier.


I slipped the back part of the J-block into the notch and drove two nails at the top.


I pulled the siding away from the wall and drove two more nails down low.


Then I nailed the lower piece of siding in place.


I re-attached the upper piece of siding using the siding J-tool seen earlier.


I set the electrical box in place and drilled a small hole through the cable clamp.

The purpose of this hole is simply to mark the center of the larger hole.


Then I used a 1½" spade bit to drill a large hole in the OSB wall sheathing.


I set the box in place to make sure the cable clamp would fit inside the hole.

No problem.


I threaded a piece of 12-2G cable through the hole and into the box. Then I tightened the cable clamp to hold the cable securely.

Before fastening the box to the wall, I ran a bead of caulk around the back of the box. This should keep water from getting inside the wall.


I set the box in place and drove 4 short wood screws through the holes that I drilled earlier.


I slipped the outer part of the J-block over the electrical box and snapped it onto the back part..


The project after the J-block was assembled.


Then I fastened this large cover onto the electrical box. This cover is approved for wet weather use while a power cord is plugged in to the outlet.

Older outdoor box covers were never meant to be used with a cord plugged in while it's raining.


More Info:

Tools Used:

  • Basic Carpentry Tools
  • Vinyl Siding Removal Tool
  • Cordless Drill/Driver
  • Small Drill Bit
  • Cordless Impact Driver
  • Electric Drill
  • Spade Bit, 1½"
  • Caulk Gun

Materials Used:

  • Vinyl Siding J-Block, 2-Part
  • Roofing Nails, 1¼"
  • Outdoor Electrical Box
  • Wood Screws, 3/4"
  • Caulk
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Written January 10, 2008