Wiring an Existing Home — Structured Home Wirings

Wiring an Existing Home - Structured Home Wirings

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.

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.

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.

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 2×4 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.

Fishing wires through the ceiling

Wiring an Existing Home - Structured Home Wirings

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).

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.

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


Leave a Reply