I'm fishing through exterior walls, between floors. I've already ran ethernet from the attic down into the second floor (top right picture) but I can't figure out how to fish it through the space between the second floor floor-joists (green box). See image below.

I'm working with a 3/4"-D 52" long augur bit, a Magnespot, and a Teslong TD500 borescope (no hook attachment though).

On the first floor, I've drilled through two top plates and have hit insulation (verified with borescope). I looked inside the walls at the bottom plate on the second floor but saw no holes so I'm guessing I've drilled into the cavity between floor joists.

I'm not a framing carpenter so the "conventional framing", shown below, is my best guess for how this house was framed (this house was built in 2000, Massachusetts). I've made sure there's no power around the work area and turn off the room's breaker when working.


And the outside of this exterior wall: ExteriorWall

And stud/joist locations from the first floor: StudJoist

I have three thoughts:

  1. Just install my security camera where the ethernet drop is now. Not a terrible spot and higher than I would like (it's about 25-30ft off the ground, above a garage). I was hoping to drop it into the dining room where it'd be just above the garage doors (11 ft off the ground) and have better visibility of the driveway (see faces instead of top of heads).

  2. Drill through the bottom plate on the 2nd floor, into the cavity. On the first floor, remove the crown molding and cut into the drywall in the ceiling, 4" away from the wall, to create a 6"x8" access hole. I've never cut into the ceiling but I can't imagine there'd be plywood backing up there. The access hole should allow me to reach inside the cavity above the double top plate, clear the insulation, and route the line.

  3. (This worked!). Drill through the bottom plate, run a string with a small magnet attached to the end through the hole into the cavity. From the 1st floor, stick a small diameter (so as to be flexible; 1/4") metal rod up to catch the magnet.

Option 2 doesn't sound too bad, provided patching the access hole in the ceiling is just as easy as patching drywall on a wall. Never done it before so I'm a bit hesitant.

  • Does the house have a basement? Is there an area where the chimney if framed?
    – Gil
    Feb 4, 2023 at 2:09
  • Gil - Yes we have a basement. We have a gas fireplace but it's on the opposite side of the house. I don't think there's ducting in this room and the room immediately below.
    – Minh Tran
    Feb 4, 2023 at 2:49
  • Re: #2, don’t remove the crown if possible. If the joists aren’t parallel to that wall, you can give yourself more room to tape and skim by pushing the hole further from the wall. If parallel, well, you are kinda stuck with a smallish hole, though it can be bigger in the direction the joists run. Feb 4, 2023 at 12:36
  • Why not just exit "where the CAT6 drop is now", run some exterior-rated CAT6 along the bottom of the siding panel to the corner, down the corner, and across the bottom of the siding panel to "where I would like CAT6 to exit?"
    – Huesmann
    Feb 6, 2023 at 15:43
  • 1
    @Huesmann That was a back-up option. Not as clean of a look but having a connection in the walls would allow me to run CAT6 into the dining room, in case I never need to put a switch/router down there (wifi extender/TV).
    – Minh Tran
    Feb 7, 2023 at 16:25

4 Answers 4


I like to call this "laparoscopic cabling." Just FYI, this location being an exterior wall makes it extra challenging!

Study the building a bit:

  • Figure out the height of your 2nd floor's floor joists. You can do this by measuring vertically between a pair of windows outside, then subtracting the height of the walls inside. Depending on the design of your stair case, it may be possible to measure indoors from 2nd floor to 1st floor, then subtract the height of the 1st floor ceilings.
  • Confirm that the walls in 2nd floor and 1st floor are the same thickness (is the casing on the sides of the window the same depth upstairs and downstairs?). If they're different you'll need to account for some offset.
  • Verify that your work on the two floors really is aligned. Measure from the adjacent exterior wall ("around the corner" from where you're working), add any offset if there's a difference in thickness of the wall framing.

Insert the glow rod from the first floor going upward. A sharp, stabbing motion should persuade the glow rod to penetrate through the insulation. Use your knowledge of the height of the floor joists overhead to measure as you do this and confirm that the glow rod went in far enough to reach the bottom side of the subfloor above. Secure the glow rod so that it gravity won't pull it down when you walk away. Tip: I always tie a loop in some mason's line and attach it lightly with tape to the end of the glow rod. That way, when I finally lay eyes on it with the borescope (to which I've attached a hook positioned in view of the camera), I can use the hook to grab the loop and pull the string through. The string is then used to pull the cable.

Go have a look into the joist space from upstairs with the borescope. If this were an interior location the insulation would be laying horizontally just above the ceiling, likely with some air space above it. Because this is an exterior wall the insulation you're hitting is probably installed vertically pressed up against the rim joist. Hopefully the tip of your glow rod will have exited the insulation and will be visible on the camera, but you may not be so lucky.

And.. hopefully that gets you through. If there's no sign of the glow rod, double- and triple-check your measurements to be sure your 1st floor and 2nd floor work is aligned.

Rim joist insulation could cause you a lot of grief. As an alternative to the glow rod, try some stiff wire. Steel, like a coat hanger, is better than copper because it's stiffer. Bend it into an arc. Orient it so that when the wire is inserted that through the hole at the top of the 1st floor wall and continued through the hole in the top plates, the tip of the arc will exit the rim joist insulation and be visible in the open joist cavity.

One parting idea: the upper room has carpet. Pull that back away from the wall in the corner where you're working and drill a hole through the subfloor a few inches in front of the wall. This gives you a new vantage point from which to view the joist space with your camera. That may help puzzle out the solution. When finished you can reattach the carpet, covering the hole without any need for repair.

And.. you're right. There can come a point at which you'll be faster to just cut a hole in the ceiling and repair it rather than continue the fight with the fishing.

Edit: and now, more thoughts..

You have vinyl siding?? Why didn't you say so?! :-) There are a hundred different ways to route and conceal UTP cable on or in a vinyl-sided wall. Admittedly, one should use outdoor-rated cable for this though. The trim that runs up each corner of the house has a nice big gap into which the cable may easily be pressed. A cable running horizontally beneath a lap line on the siding disappears fairly well; you could also run cable horizontally behind the siding almost as easily. The cable could emerge from attic to exterior, then surface route down to where you want the camera to be. You can even use a siding removal tool to "unlatch" one course of siding from the next, giving you access to route the cable behind the siding.. or to cut holes in the sheathing for easy and restoration-optional access into the wall cavities!

I might cut enlarge one of the drywall access holes to be about 24" tall and use a 36" drill bit. This gives room to drill through the first wall plate and then get the drill into the wall so there's no bend in the drill bit. You can then be more confident about drilling blind through the other wall plate with good placement and angle.

  • Thanks for the tips, Greg. From the outside, that exterior wall is completely flat: from the the basement/garage/ground-level all the way to the attic - no overhang or anything, about 35-40 ft tall (will upload a photo tomorrow). I'm fairly certain the walls are the same thickness (1/2" sheathing, 3.5" wall cavity, 1/2" drywall). Since the exterior wall is flat, there's probably no offset and it's just as the diagram in my OP depicts. Will verify.
    – Minh Tran
    Feb 4, 2023 at 4:16
  • Pulling back the carpet for the peephole is a great idea. I'll give that a shot if it comes to it.
    – Minh Tran
    Feb 4, 2023 at 4:37

Use a flexible and extremely long fish bit. Drill through both plates at once. Now tie the cable on to your bit, and pull it back through.

Aligning two separate holes is just too hard!

  • Yeah, you will frustrate yourself and spend an entire day trying to fish blindly through that. Buying a cheap fishing drill bit will be well worth it.
    – Evil Elf
    Feb 4, 2023 at 13:30
  • 1
    Cool trick that sometimes works with those long flexy bits: poke through a tennis ball to help the bit center itself (somewhat) on the plate. Feb 4, 2023 at 14:43
  • This idea is a contender but it's a bit risky since top plates, being 2x4s, are only 3.5" wide. The rim joists take up 1.5" so there's only 2" of plating left for drilling that'll get me into the walls. Angles are in my favor since the insulation will tend to push the bit against the rim joist, which is what I want guiding the bit anyway. As long as the bottom plate is aligned with the top plate, I should be able to drill through all plates.
    – Minh Tran
    Feb 4, 2023 at 14:56

I pulled the carpet up to reveal the subfloor and saw the first hole coming through the baseboard. Right behind the hole was the bottom plate. I'd missed it by about 3/4".


I couldn't use this hole but it did give me a chance to stick my borescope into the cavity to take a look. The framing was just as the the diagram in my OP depicted.

With a better idea of what was below, I drilled top-down through the bottom plate into the cavity. At this point, I didn't want to keep going and drill blind because I might hit the ceiling. The two holes that broke into the cavity weren't aligned (no surprise) but I had positioned them close enough together with the magnespot.

enter image description here

The holes were 3/4"-D. I duct-taped (3) 1/2"-D neodymium magnets to a stick (fiberglass driveway marker) and stuck it up the top-plate. I duct-taped (3) 1/2"-D magnets to a pigtail electrical cord that was semi-rigid and fed it down the bottom plates. The magnets were oriented so that when they attracted, the whole thing was in-line.

Being neodymium, the connection was decently strong. If the holes were smaller/angled (friction against the hole's walls) or the insulation thicker/deeper, I don't think the magnets would have held on. But it worked.


  • I have used magnets and/or steel bits on inside/outside of drywall to drag a pull string before. :)
    – Huesmann
    Feb 7, 2023 at 20:49

It appears going down through the basement might be the easiest route. I put about 30 CAT5 openings with several Cat5 and RG6 cables in my 1970s home about 15 years ago. It was a bit tricky but I could not go into the attic (handicap problem) so everything is in the basement. I would locate and cut a hole in the wall, conscious of where the studs were. I then I took a very small drill and drilled through the floor. I then pushed a stiff thin wire through the hole. In the basement this gave me a reference point to drill up. Most of the time I had to drill at an angle to come between the wall and the outside sheeting. When finished you had to know where to look to find the hole in the floor. The most used tool other then the drill was a piece of coat hanger wire.

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