How to cut drywall for access around a switch box already in the wall?

Question

I have a 1-gang metal box at the top of my basement stairs for the light switch. It is secured to a stud on its left side. The electrical panel is on the far side of the house on the basement.

Hence I have to run 14/2 cable 30ish feet horizontally along the basement ceiling and 4ish feet up inside the wall to the switch. Then I have to run more wire 4ish feet right back down and then to the receptacles for the lights in the basement.

As far as I can tell, the only way to be able to attach the new incoming and outgoing wires to the switch is to open up the drywall around the box so that I can have access to do things like fish wires up from the basement, attach things with proper cable clamps and wire nuts, wire the switch properly, and whatever else needs to happen.

I do not have an oscillating multitool yet, so I plan to use a manual drywall saw to cut as much hole as I need.

How big a hole around the box should I cut so that I can reach all the sides with room to work on splicing and screwing and whatever else?

Answer 1

1. Avoid cutting right near the box. It's much more difficult to patch that well and end up with a flat outcome. You can still install clamps by reaching.

2. If you're making a hole, make a hole. Give yourself lots of room, but still steer clear of other devices, corners, etc. Stay in the field. A 12" x 12" hole would be nice.

3. Plan for replacement. If you do this right, you can put your cutout right back in place with minimal backing fixes. Either cut between all backing and float scrap wood to reinstall, or cut over the center of backing such as studs so you can simply screw it back in. Which you prefer may depend on what saw you're using, etc.

You also asked how to repair the hole, but that's a bit much for one post. See the many existing answers on this site that cover that process.

Answer 2

A few random bits of advice that might help.

• It is possible to fish wires into boxes without cutting walls open. Possible, easy, or hard, depends a lot on the exact situation. If you are starting from an unfinished basement ceiling and only going up to the next floor, that's a great start. If the box has a side or bottom knockout with access to a stud bay that's another plus. You need to investigate.
• If you don't mind doing some drywall repair and painting, that makes fishing a LOT easier. My only advice is, don't use power tools to cut drywall in any room that isn't part of a major renovation. Drywall is very easy to cut with a hand saw, and cleaning up the mess from an oscillating saw is not easy at all.
• If you have to cut a box out of the wall, you can cut the hole to the size of an old-work 2-gang box (or 1 gang up from whatever you're doing) and just install a bigger box with no drywall repair. Aaaand if you're running new cable for a light switch, you will of course have a neutral there so for a staircase a good thing to put in the extra space is a Decora night light.

Answer 3

With regard to drywall patching, here's an approach that I have found is effective:

1. Cut a square/rectangular piece of drywall that is larger than the hole you want to patch.
2. Place the patch piece over the hole and trace around the patch with a pencil
3. Open the hole to match the traced line
4. Find pieces of scrap wood such as furring strips.
5. Attach the scraps around edge of the opening with drywall screws. Usually, two pieces that span the opening can be placed behind the hole and secured on two sides.
6. Place the patch in the opening
7. Add screws to the patch and secure it to the strips
8. Mud the (hopefully small) gaps around the patch and the (slightly buried) heads of the screws.

Answer 4

If you know for sure where to drill the base plate, do that, then you can push a pair of cables up into the wall. Have a helper push cables; with some maneuvering and pre-bending of the cables you might be able to catch them with a hooked tool (even another piece of wire) and guide them into the box, using that small space between the box and drywall.

If doing this with the wires doesn't work out, consider investing in a fish tape. Run the tape up the wall, snake it into the box, attach your cables, then with your helper pull the cables back down.

Looking at the photo, you may encounter another problem: the box may not be deep enough to hold all that stuff and the switch. Consider putting in a deeper box. In this case, cut away the old box and pull the exiting cables out, which will give you a big enough hole to get your hand in. Breaking out the old box isn't too difficult if it's an old Bakelite box; if it's plastic you'll need to nip away at it with cutters to free the wires, then pry it out. With the box out you now have enough room to get your hand on your new cables as your helper pushes them up the wall.

Install an old work box, which doesn't need to be attached to the stud but instead clamps onto the drywall. First, thread the cables into the box, then push box into the wall. Tighten the box screws, make up your connections and you're done.

If you don't mind patching drywall, cut away a piece about 12" high (4" above and below the box, plus 4" for the box) and width between the studs (16"). On the right side, cut to the center of the stud; on the left cut on the center except for the part next to the box.

This will give you full access to the box. If you find that you need to get a bigger box, you have more room to easily pop out the old one and install a new 'new work' (nailed to the stud) box.

To make the cuts use straight-edge and a utility knife first to score the drywall, then finish the cut with a small, thin blade saw. Do this carefully and save that piece; you're going to put it back later.

Fish your cables and if needed put in the bigger box (make sure you dry-fit with your removed piece.) Re-install the drywall with screws onto the studs, patch with compound and fiberglass tape and finish.

A tip: you can cover up less-than perfect drywall around a box by using a larger cover plate: either a "medium" or "jumbo".

Answer 5

With regard to drywall patching, here's an approach that I have found is effective:

1. find paint that matches your walls current paint job. Ideally the last person who painted the thing saved some, if not:

   • use a phone app to find a color match( home depot has one, pantone has one, valspar has one, sherwin-williams has one, amazon has one)
   • Or better yet just bring your patch piece to your local paint store.

2. Cut out your hole out carefully, the bit of drywall you just removed is your patch piece. (note its easier to fix a hole that is too big.. than one that was too small the first time you cut it).

3. Find 2-4 small pieces of scrap wood. Attach the scraps around edge of the hole you made.

4. put your patch piece into the hole, the wood strips prevent you from dropping the patch piece inside of the wall.

5. screw the patch in place with the screws.

6. lightly sand the area (So that mud will stick) + a bit around the spot you placed the patch piece.

7. then mud over the entire thing.

8. retexture.

9. repaint.