How to Feed Cable Through Insulated Walls

It's not as hard as you think. Here are a few handy techniques.

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By Grayson Evans
October 29, 2008
Many installers seem to have a real fear of insulated walls. Fear not.

Drilling up or down and fishing cable through insulated walls is an inconvenience, but nothing more.

Sure, there are certain techniques you can't use through insulation, but there are always work-arounds.

What Are Insulated Walls?


What exactly are insulated walls? They:
  • are mainly wall cavities filled with fiberglass batt insulation
  • were used in nearly all homes starting in the early 1960s, usually in outside walls or in walls that divided "conditioned space" from unconditioned space
  • are almost always associated with applications where in Sheetrock is used as the interior wall covering
Older homes tend to have either no insulation or to have been retrofitted with something like blown-in fiber.

This stuff is usually no problem; it just makes a mess when you make a decent-sized opening in the wall. You will often find it has all settled to the bottom of the wall.

Some newer homes have expanded foam in the walls. This is not impossible to deal with, but difficult.

Where to Drill


Regardless of whether you're drilling up or down in an insulated wall -- from an opening in the wall or into the wall cavity from above (through top plate) or from below (through sole plate) -- the place you want to aim for with the bit is in the corner of the wall cavity.

If you're drilling up from an opening you've made for an outlet or speaker in the Sheetrock:
  1. push the bit through the insulation, using short jabs, at an upward angle, toward either back corner
  2. if there is paper, foil or plastic on your side, just cut through it
  3. when the bit hits the back corner, walk the bit into and up the corner by giving the drill short bursts (forward or reverse, whichever works better)
If you can keep the drill in the corner, you'll have no trouble with the insulation.

If you're drilling down into a basement or crawl space from an outlet opening near the floor, use your drill guide to keep the bit in front of the insulation and aim it into one of the front corners.

If you're drilling into the wall cavity from above or below:
  1. try to make the hole near one of the corners. Sometimes the best corner to use depends on the insulation
  2. if there is no foil or paper backing, it doesn't matter much
  3. if the insulation has a foil or paper backing, then it may have been installed by stapling the paper/foil to the inside of the studs (see here).
This creates a nice open space on either stud near the Sheetrock. Try to make your hole here (use a spring steel "feeler bit" to locate the exact spot).

If the insulation was stapled to the outside of the studs, then there is usually a nice open space in the center of the wall cavity. This makes fishing the cable up/down much easier.

3 Cable Fishing Techniques


Once you've drilled the holes, fishing is actually easy. There are a few ways to do it.

Technique #1
If you are fishing the cable up or down from an opening in the Sheetrock, then you want to follow the same path you made when you drilled:
  1. Use a fiberglass rod with a bull-nose end. If you're fishing a small cable (like a security cable), you can attach the cable to the end of the rod by threading one of the wires in the cable through the hole in the bull-nose. If you need to fish a larger cable or bundle (or if your buddy is going to feed the cable to you from above or below), thread a pull-cord through the bull-nose.
  2. Push the rod to the same corner you used with the drill bit. The rod will follow the corner and pass through the hole the bit made. Your buddy attaches the cable to the pull-cord and you pull it back down with the cable.
  3. If you are feeding the cable up or down into the wall cavity from an attic or crawl space, attach the cable to a fiberglass rod and get the rod into a corner -- preferably a corner on the same side as the opening to which you're trying to fish. Again, this can be made easier by fishing down a pull cord and then retrieving the cord out from the opening.
  4. Attach the cable to the pull cord in the attic/crawl space, and pull the cable out with the cord.
Technique #2
  1. Attach a ball-chain to the end of a rod using a screw-on attachment. You can use several feet of ball-chain. Measure how much you need to feed the rod up or down the wall so that the chain will be located to the left or right of the opening you made in the Sheetrock.
  2. Feed the rod down the corner. Now you can use a magnetic retriever tool (going in sideways from the hole to the place where the chain will be located). If you feel around, you'll hit it.
  3. Slowly pull the retriever out with the chain attached. Keep the magnetic retriever against the inside of the Sheetrock.
Technique #3
There's another interesting way to fish a cable into the cavity from above/below that involves using strong magnets.

BES Manufacturing's "Wire Python" is a good example.

The tool consists of two parts: a "paddle" magnet and a "wire leader" magnet. These magnets are so strong that they will easily grab each other and let go through the Sheetrock.
  1. Attach the cable you want to pull on the "wire leader." This has a hook for the wire with a strong magnet attached. You can push the wire leader with the cable attached toward the Sheetrock (or the side with the opening).
  2. Hold the paddle magnet against the wall and move it around a little until it latches onto the leader magnet.
  3. Then, using short pulling motions, pull the leader magnet right through the insulation to the opening.
Grayson Evans is the founder of The Training Dept. He can be contacted via e-mail at .(JavaScript must be enabled to view this email address).


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