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Running Wires in an Existing Home

  This guide explains how to fish wires through walls on an existing home - after the drywall is installed. You may also want to read some of our other guides for more information. The Wiring Panel makes the case for terminating all wires to a central location instead of running wires room to room. The Types of Wires page explains the different types of wires you may be using. The Finishing Guide explains how to terminate the wires (put on the end connectors) after you run them to the outlet. The Parts Guide lists what you need to do the project. Minimally, you will need a fish tape, electrical tape, a drywall saw, and a stud finder. You may also need a hammer & chisel if you will be notching studs or joists.

Planning your wiring run

  First you will need to decide on the start and end location for your wire and then determine the path that the wire will take. It is important to consider the wire path before cutting any holes. Some flexibility in the outlet location could make a difficult wire run much easier. Some things to consider when running the wire:

  • Use a stud finder to determine the exact locations of studs in the wall. Studs are 1 1/2" wide and will usually be 16" or 24" apart (except need windows, doorways, and other walls). Make sure you don't cut your hole right over a stud.
  • Determine what is on the other side of the wall. You may need to do some creative measuring to find the same spot on both walls. Sometimes it is easier to count studs on each wall instead, knowing that they are either 16" or 24" apart. Outlets will not fit back-to-back in the same wall. A medicine cabined could interfere with an in-wall speaker. Duct work can interfere with everything.
  • Next determine what is inside the wall. If this is an exterior wall, then it will be filled with insulation. This doesn't mean you can't use it but it makes fishing wires more difficult. You should also go into the basement or attic to see what pipes and wires go through that wall. You don't want to cut holes for a speaker only to find water pipes for the upstairs bathroom running through that wall. Also, outlet locations should give you a good idea of where the wires are. The power outlet will be mounted to a stud, and the power wire will be run either up or down from that stud. Any cable, internet... wires should be run at least 12" away from a power wire. When your wires need to cross an electrical cable, it should do so at a 90 degree angle.
  • Another problem is fire stops running horizontally between two studs. These boards could prevent you from running a wire down that wall. Builders will also sometimes use horizontal 2x4's on either side of a door to prevent the wall from shaking when the door is slammed shut. The best way to locate a fire stop is to use a stud finder up and down the wall where you will be running the wire, especially if this wall is right next to a door.
  • For wires that are run inside walls you should purchase fire resistant wire that is rated for runs through multiple floors. For wires run near the flue you may want to purchases purchase rated wires.
  • Do not cut the wire from the spool until you are done the wire run. If you cut the wire and then run it you will almost always cut it too short. It is best to not cut until you are done (or at least partially done) and then you should add a couple of feet to your estimate.
  • Finally, be sure to read through this entire guide before you start cutting. The Structured Wiring page also has lots of helpful tips on identifying wires, pipes and ducts with pictures of what they look like before the drywall is installed. You may also want to find a home under construction in your neighborhood to walk through to familiarize yourself with what the walls look like on the inside.

  Now that you understand what is in the wall, determine if your chosen outlet/speaker location is best. Would moving the outlet on the other side of a stud in either direction cause more or less problems? Are there so many problems that the wire cannot be run? There are alternatives for very difficult installations. Acoustic Research makes a flat speaker wire that sticks to your wall that you can paint over. If necessary, you could run the wires tucked under the baseboard around the outside of the room.

Cutting the holes for outlets

  At this point you think you know what is behind the wall, but you can never be sure. That is why I don't like using any power tools to cut through the drywall. Instead I use a utility knife / razor blade with the depth of the blade set to the thickness of the drywall. For an outlet I first make a 1" x 1" hole in the center of the box using a utility knife. This hole is big enough that I can see and feel around for any wires or pipes but small enough that it is easily patched in case I have made a mistake. Once I verify that there is nothing wrong, I trace out the electrical box and then cut the rest of the hole using a sheetrock keyhole saw or a utility knife. I also like using a utility knife to cut drywall on external walls. That way it does not cut through the paper barrier of the insulation.
Old Work Electrical Box with tabs
  When tracing out the electrical box, don't include the tabs on the top or the bottom. Remember to pull the wires through the box before putting the box in the hole. Then tighten the screws on the front of the box to open the tabs/flaps and pull them toward the drywall. This is what it should look like from behind the wall when you are done.

Back of Old Work Electrical Box with tabs

Drilling to access the wall from above or below

  If you have access to your basement/crawl space and attic, you should be able to run wires without having to cut & patch any drywall. On the second floor run wires down the wall from the attic. On the first floor run wires up the wall from the basement. When necessary, use existing ducts or pipe runs to get wires from the attic into the basement. This will all be covered in detail below.
Fishing a wire from second floor to first floor through the attic and basement

Red: Wire from the attic to the basement near the flue
Blue: Wire from the attic to the basement using a second floor HVAC return
Green: Wire from the attic to a second floor outlet
Purple: Wire from the basement to a first floor outlet


  For a first floor installation you will be drilling up through the floorboard and then sole plate. From down in the basement the bottom of the floorboards don't give a good indication where the walls are. Measuring is almost impossible. Remember that 2" off in either direction and you are drilling through your rug. A good way of marking where to drill the hole for your wire is to first drill a small pilot hole from the first floor into the basement. Right under the outlet where you want the hole for your wire, drill a small hole under the baseboard moulding at the joint of the wall and the floor. Then push a thin wire (or a coat hanger wire) through this hole and then find this wire coming through the ceiling in the basement. This wire should come out right under the drywall. The studs are 3 1/2" wide so move 1 1/2" - 2" in towards the wall to get the center of the stud. Again, remember to look before you drill this pilot hole. You should have a rough idea where the drill bit will come through the floor. Make sure there are no wires or pipes in that area in the basement. Also don't unnecessarily push the drill bit all of the way through the floor. The floor will only be 3/4" thick at most.

  Second floor installations are easier because you will be able to see the double top plate from the attic. Be sure you drill straight down through these boards. I've actually run into triple top plates (5 1/2" total thickness), and a small angle on the drill can cause you to come out through your ceiling or wall instead of being between the studs. Note: Always wear a face mask when around fiberglass insulation in the attic.

  Sometimes drilling from above or below is not an option. Maybe you don't have a basement or an attic. There are flexible drill bits that are designed for this very purpose. These bits can be up to 6 feet long and can be used to drill through several studs or joists at a time. Cut the hole for the outlet and then stick the flexible drill bit through the hole to drill up or down or sideways through the studs. Note that determining what is inside the wall is even more important when using one of these long flexible bits. If you drill through 3 studs at a time without being able to see what is between them, you could easily drill through a pipe, electrical wire or ductwork. Look for vents, outlets, sinks... above and below where you are drilling (on all floors) to determine if something might be in that wall.

Flexible Drill Bit


Fishing the wires through walls

  Now you should be ready to fish the wire. This is usually a 2 person task. From the basement or attic, push the wire fish tape through the hole you have drilled. Have someone at the other end reach through the hole in the drywall, grab the fish tape and pull it through with about a foot sticking out of the hole. Then attach your wire to the fish tape and pull it back through.
Connecting wire to fish tape

  To correctly tape a wire you should first strip off the insulation. Then wrap the wire around the hook on the fish tape as shown above. Finally, tape everything using electrical tape. Make sure there are no bulges in the wire that will cause it to get stuck when pulling it through. Be sure that the the wire is taped on tight or it may come lose in the wall and you will have to start over. Most wires (especially coaxial cable) shouldn't be bent at extreme angles. After pulling the wire through cut off the bent portion of the wire and throw it away.

Running wires from the attic to the basement

  Now that you have run wires from your outlet to the basement or the attic, you may need to run the wire from the attic to the basement. Ideally, your house included a future tube which is a PVC pipe running from the basement to the attic specifically for this purpose. If not, then you will need to find an existing pipe or duct that already runs the full height of the house so you can run your wire in the same area. This could be the flue for the furnace / hot water heater, a radon tube, a water pipe, a heating duct / return, or a fireplace chimney. Do not cut into the flue or the radon tube because this could release harmful chemicals into your home. Also, the flue and chimney will get very hot and could set your wires on fire. This guide will cover two different methods: running the wire near the flue (red wire in above example) and running the wire in a second floor HVAC return (blue wire in above example).

  If you must run wires near the flue, maintain a minimum 1" distance from the flue at all times and use plenum fire resistant wire. For a chimney flue, the wire should be 12" from the flue. From the attic, lower the fish tape all the way to the basement, connect your wire, and then pull it back through. Secure the wires tight using wire staples at both the bottom and top of the run to make sure that the wire doesn't bow in the middle and get close to the flue. Sometimes there is a horizontal square piece of sheet metal mounted to the floor boards to hold the flue in place. If you must drill through this, be sure it is at least 1" from the flue itself. The sharp edges from this hole could cut the wire over time, so use a grommet to protect the wire. You could also cut the edges of the hole with tin snips and bend back the rough edges. Consult your local building codes for more information about running wires near a flue. Building codes vary between different cities and counties. Improper wiring could cause you to fail a home inspection and prevent you from selling your home.

  Running the wires through a HVAC return is more difficult but it is also safer. First, find a return on the second floor on an internal wall that runs the full height of the house. Basically, this means finding a vent (like the one below on the left) where you know there is a wall on the first floor directly under the one on the second floor. Remove the screws and take the grill off the wall. With a flashlight and a mirror look down the wall to make sure there is a clear path all of the way to the basement. Builders will use the space between the studs and the drywall to form the return duct, so no sheet metal is required for the return until you get to the basement. The next step is to find the bottom of this duct in the basement. It will most likely be covered by a piece of sheet metal nailed to two joists as seen in the picture below on the right. Pry the sheet metal off using either a claw hammer to remove the nails or a flat head screwdriver to pry the sheet metal. There is no need to remove it entirely. Just enough to run a wire through it. Once again, shine the flash light through the return on the second floor and make sure you can see it in the basement to verify that it is the correct duct. Now that you know the duct will work, drill a hole through the double top plate into the attic. I prefer to stick the drill into the vent and drill up into the attic instead of drilling down from the attic. Just don't drop the drill. Before drilling, go into the attic and find the top plate 2x4 that is right above the vent and make sure there are no wires running directly above it that might get cut by the drill. Now you are ready to run the wires. You may be able to let gravity do the work and just push the wires down from the second floor vent and then push the other end through the hole into the attic. If that doesn't work, use the fish tape. When you are done running the wires, nail the wire to one of the studs so that it isn't visible through the grill on the return.

Return grill in wall     Return duct in basement

Fishing wires through the ceiling

  If you need to run the wire to a first floor ceiling (for a ceiling speaker), then you are going to have to cut and patch some drywall. How much drywall you need to cut is based on how well you select the wire path. Using a stud finder, determine which way the joists run the ceiling. You want to run your wire with the joist (green wire below) instead of against the joist (red wire below).

Fishing Wire To First Floor Ceiling

  You will first need to drill a hole from the basement through the sole plate into the area between the studs, as if you were wiring a first floor outlet. Make sure you have a drill bit large enough for all of the wires that you are going to run. Usually a 1" bit will let you run several coaxial and cat 5 wires. You will then need to cut and remove an L shaped piece of drywall above that hole where the wall meets the ceiling. When cutting the drywall try to cut it out all in one piece and do as little damage as possible. Reusing the cutout section will make patching the drywall easier. Using a hammer and chisel, notch a path in the top plate of the wall so that a wire can be run from the wall to the ceiling. Then fish your wire from the basement to the top of the wall and pull it through into the room.

Fishing Wire To First Floor Ceiling

  If your joists are not running the right way, then try running the wire in a different wall instead. If you must run your wire against the joists then you can either use a long flexible drill bit, or you can cut out a section of ceiling drywall at each joist and notch it with a hammer and chisel to make room for the wire. By code you cannot notch any joist 2"x6" or smaller. Above than, you cannot notch more than 1/6th of its height. In reality, you shouldn't need to notch more than 1/2" anyway.

  After notching a stud or joist, cover the notch with metal plate so that you can't later accidentally drill or nail through it. Then repair the drywall above the plate using the same piece of drywall that you cut out and some spackle.

  The last step is to cut the hole for the speaker. Use a stud finder on the ceiling to locate the joists. Ceiling joists can be 12" apart or even closer. Sometimes there is barely enough room for a speaker between the joists. For speakers, I prefer to first cut a small pilot hole (just like the outlets) in case the hole is in a bad location. Using that small hole, verify that there are no ducts or water pipes in the ceiling that would prevent you from mounting a speaker and make sure the joists are really where you believe they are. Then trace out the speaker hole using the template provided with the speaker and cut out the ceiling drywall with a utility knife or a sheetrock keyhole saw. Use your wire fish to get the speaker wire to the hole for the speaker and then attach the speaker wires by following the directions that came with the speaker.

  To use the flexible drill bit, first cut the hole for the speaker and then push the drill bit through that hole and drill through the joists from the speaker hole to the wall. If the bit is not long enough, you may also need to drill from the wall back toward the speaker. The more joists that you drill through the more difficult it will be to fish the wire later. You will be drilling between joists without knowing what is there, so determine if there are any walls (with electrical outlets, ducts...) or any bathrooms above this area on the second floor. If there is any chance that there might be any plumbing, electrical wire, or ductwork between the hidden joists, then it is probably safer to cut the drywall and notch the joists instead.

  You should also check out our page on running the wires on a new home, which has lots of real photos of what you may find in your walls.

Finishing up and other notes

  
Insulate the electrical boxInsulated Electrical BoxAfter the electrical box is installed and all of the wires are pulled through, use some expanding foam to fill the holes in the electrical box to insulate it..
Wire Staple With Zip TieWire Staple with Zip TieAny time you are attaching a wire to a stud or joist, use both a wire staple and a zip tie. Nail the staple into the wood and then use the zip tie to attach the wire to the staple. That way the sharp staple can't damage the wire.
Engineered JoistEngineered I JoistSometimes these engineered joists are used instead of 2x10's or 2x12's. These joists are stiffer and quieter than conventional lumber. Engineered joists CANNOT be notched. Instead you must drill holes through the middle of the joist. Some have pre-made punch outs so that you don't have to drill. if you do drill your own hole, make sure it is at least 6" away from the end of the joist.
Engineered HeaderLaminated Veneer Lumber - Engineered Beam or HeaderOversized engineered beams are rarely used in homes except when special conditions require it. Some types of these beams can be drilled through and some cannot. The safest bet is to never notch or drill through a LVL Engineered Beam.
Aluminum FramingAluminum FramingAluminum studs should not be notched or drilled through. Instead use the pre cut holes in the studs to run your wires. The premade holes shouldn't have any sharp edges. If the edges are sharp and there is no grommet covering the opening, then you will have to get your own or run your wire inside metal conduit.
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