Electrical question - how to add a switch to a exterior wall box

[Mason]

I want to add another switch to a box on an insulated exterior wall. Is there any way to add another box beside the existing one? I would prefer to not just have another box in the wall a few inches away from the existing one. I have done this with an interior wall but never an exterior one.

I have considered cutting the Sheetrock and removing the existing one and installing a double gang box with the vapor barrier seal around it but that seems like overkill.

[John Mihich]

There are dual switches out there. They take up the same space as an outlet. I have used them a few times. Of course if you are already using them then I think if you want to add another switch I would do this. Cut out the existing box - you're lucky if the box is plastic. Enlarge the opening to accommodate the larger box. Buy a retro fit box and wings (can't remember the name). The wings will help hold the new box in the hole. Or buy a box that has clamps on the side that get tight when you tighten the screw - similar to butterfly drywall anchors. There are other boxes but those are the two I have used the most.

[crokett™]

the retro fit box is sold as an 'old work' box in Lowes or HD. I've done what you are proposing. You can get the old box out and cut the hole larger to accomodate an old work double gang box. Having the dual-switch fixture in the single gang box would be easier.

[Mason]

Unfortunately I can't do the double switch in a single gang box. I have a special dimmer I need to install. I looked at the clamp on boxes but haven't seen one that is designed for an exterior wall. I think my best bet is to cut the Sheetrock around the existing box, remove it and install a double gang one.

[Mr_Mike]

Post a pic so we can see the wall. Exterior siding type can make a difference in how you finish it off. For me, that would be stucco, and if your careful, no wall repairs necessary.

You can do this without cutting the inside drywall. It just takes a little imagination.

First remove the existing box:

Using your replacement box, make the size of the new hole and cut out the siding/underlayment/whatever to expose the wall innards. I'd use a vibrating multi-tool. Mine is HF, and works fine. If possible, verify wire location so you don't damage it.

If the box is plastic, use a sawzall against the stud and cut the top and bottom nail. Slip the blade between the box and stud at the center and slide up or down until you find the nail. Use a fine tooth metal cutting blade, not a wood blade. Be very careful not to over cut and nick the wire, which should be nailed to the stud nearby. I presume a metal box is similar, but its been a while since I've come across one.

Replacement: Use a NEW work box. Cut off the nailing ears. (You already have a sawzall and a multi-tool, right?) Drill two mounting holes on the stud side and predrill for drywall screws. Put box in hole and screw into stud. The holes should be far enough in the box to hit the stud, but not so far as to make a bad angle for screwing. If you can get a ratchet and bit in there to get the screw in straighter, that is preferred, but screwing in at a bit of an angle is fine. With a double box, the angle isn't bad. Single boxes are a tad more problematic.

If the box is too floppy on the unsupported side, you can add a battleship, but I"ve only needed to do that once or twice. (point in fact, you could use a eared metal box and battleships and not touch the stud too)

Place electrical tape over the screw heads. Install your stuff. Its probably advisable to pull the wires into the box in advance too.

I've done this many times. It works well.

My bigger concern is how are you going to run the wiring? I'll leave that alone for now as well as how you fix the siding, whatever that is.

[Mason]

I'm sorry I wasn't clear in my posting.
This is the inside of an exterior wall. Not the exterior side. The box that is in there is a single gang that has a seal for the vapor barrier. I want to make sure it is sealed when I add onto it so I don't get any air intrusion. In Minnesota that can be a big deal!. I could use your method to cut out the old box but it has a seal around it that will make that difficult. My house is only 4 years old.

I have access to the wall from the basement. I plan on drilling through the plate and pulling the wires up. I know it's not easy with the insulation. I will then spray foam the hole.

[Mr_Mike]

I doubt one box makes a big difference. I'd seriously consider just a foam gasket under the faceplate.

They do make vapor barrier hats that go behind boxes. Perhaps that would work.

You can also fold up some sheet poly and staple it in place. Perfection is likely not required.

Since its on the interior surface, a typical old work box can be used.

Never done a electrical box with a vapor barrier flange. Sounds interesting.

[TDKPE]

LIL

Around here, expanding foam is sprayed into all the cable entries in the box, to seal them after cable is pulled. Old work box could use a thin caulk ring around the perimeter. Between those two things, the box should be sealed from the wall cavity.

[Mason]

Mr_Mike said:

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Never done a electrical box with a vapor barrier flange. Sounds interesting.

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Probably not a lot of need in southern CA!

[JIMB49]

well i did fin a short instruction on how the way it should be done the link <a href="followshttps://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=2&amp;cad=rja&amp;uact=8&amp;ved=0ahUKEwi91qnM7dDNAhWFKGMKHcY9BAMQFghUMAE&amp;url=http%3A%2F%2Fwww.lessco-airtight.com%2Finstallation-instructions%2F&amp;usg=AFQjCNGnaU0QqKgwuA3nAsgUVWiz4odhow" >followshttps://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=2&amp;cad=rja&amp;uact=8&amp;ved=0ahUKEwi91qnM7dDNAhWFKGMKHcY9BAMQFghUMAE&amp;url=http%3A%2F%2Fwww.lessco-airtight.com%2Finstallation-instructions%2F&amp;usg=AFQjCNGnaU0QqKgwuA3nAsgUVWiz4odhow</a>