Workshop Connectivity:

Laying Conduit Between
House And Garage

 
In This Article:

A trench is dug, holes are cut into the foundations, and PVC conduit is connected between two buildings.

Related Articles:
Skill Level: 2-3 (Basic to Intermediate) Time Taken: About 8 Hours

By , Editor

 

Introduction:

A couple of years ago we decided to break up the cracked concrete between the house and the garage and replace it with paving stones. I realized that I had an opportunity to improve the utility connections between the house and garage.

I had always wanted to install a big fat conduit between the house and garage, so I could run phone lines, speaker wires, and computer network cables into the workshop. I also wanted to run a compressed air line from the garage to the house, so I would always have a ready supply of compressed air for the various pneumatic nailers I use.

Since the garage had only one 20 Amp electrical circuit, I decided to run a large electrical conduit in the same trench, so I could eventually install a large sub-panel in the garage to feed numerous circuits.

We began by digging a trench between the house and the garage.

 

The garage foundation was quite shallow. The footing (visible just behind the shovel blade) was only 24 inches below grade. Conduit trench between house and garage.

 

The view from inside the garage. A few years earlier I had installed some OSB on the walls, but I had left one section removable because I anticipated making some changes to the wiring.

 

Once I determined the entry point for the 4 inch conduit, I drilled a ring of holes with a rotary hammer set in the hammer-drill mode.

This circle is about 6 inches in diameter, enough extra to give me some wiggle room.

Cutting large hole in concrete floor slab in garage.

 

Pointed tool for concrete demolition. Then I used this pointy-tipped concrete-breaking bit in the rotary hammer to break up the concrete.

Believe it or not, this pointed bit is much better at breaking up concrete than the chisel-shaped bit.

 

You just plunge the bit into the concrete and let the tool slowly force the bit inward.

Once I had broken through the slab, I continued to chip away at something underneath.

Breaking up concrete with rotary impact hammer.

 

No Rotary Hammer?

A rotary hammer is simply a hammer-drill that can be switched into different modes: Drill only, hammer only, and hammer while drilling.

Before I bought this Bosch rotary hammer (about $325 at Home Depot), I used a budget-priced hammer-drill to drill the holes, and a sledge hammer with a cold chisel to break up concrete. Usually the manual method takes longer, perhaps 2 or 3 times longer.

But don't be deceived into thinking that this light-duty rotary hammer will break up thick concrete slabs quickly and easily. This tool is often called a "chipping hammer" because it basically just removes small chips of concrete.

 

Hole in concrete floor slab for large conduit. I discovered that the concrete block wall was made of regular 8 inch blocks, and the 6 inch thick blocks were only used on the top row.

This actually made the job easier.

 

Outside:

I marked the location of the conduit opening and drilled a series of holes. This is the first row of blocks above the footing, so the hole can't be any lower.

Cutting through a concrete footing would be too much work, and just a bad idea. It would be easier to dig under a footing than to go through it, but the soil needs to be packed tightly when the excavation is filled in.

Multiple holes in cement block wall for conduit entrance.

 

Breaking concrete block with sledge hammer. I smacked the cement block with a sledge hammer and it broke easily.

 

I used the chisel tip to bust up the surrounding cement block and mortar. Hole in cement block foundation for 4 inch conduit.

 

I used a gardening tool to reach into the hole and pull out the dirt.

 

The completed hole in the garage foundation, seen from the outside. Hole in garage foundation wall.

 

Hole in garage floor for utility lines. Viewed from inside. This hole is big enough for a medium-sized dog to crawl through.

 

I placed a 4" PVC long-radius elbow in the hole, to check the fit.

No problem.

4-inch PVC elbow used for utility conduit to garage.

 

Stone rubble foundation in old house. We continued digging the trench until it reached the house, about 14 feet from the garage.

The house is old (built around 1907) and it has a stone rubble foundation.

 

Looking through the basement wall:

I chipped out some stones from the rubble foundation. It's difficult to make the desired shape of hole, and it's easy for the hole to become much bigger than needed. 

 

The view from inside the basement.

It's hard to tell what you're looking at. The wall had been painted white many years ago, so where the mortar has been chipped away the natural color of the rocks shows through.

The red arrow points to the spot where I've broken through to the outside.

This is directly beneath the basement stairs, so it's a good place to

 

I carefully enlarged the hole until it was big enough to accept the 4" pipe and the 2" electrical conduit. Hole chipped in stone foundation wall.

 

Caution:

This wall was about 20 to 22 inches thick. There was plenty of mortar at the inside and outside faces, but in the center of the wall there was very little mortar. I'm guessing the foundation was built this way.

I was apprehensive when I started making this hole in the stone foundation... I had visions of a major section of foundation wall crumbling before my eyes. Nothing bad happened.

For a small hole in a stone wall, the stones above the hole will push against each other and hold themselves in place. I understand that as a hole gets bigger, eventually the rocks above the hole won't have anything supporting them, which might cause the rocks to shift and possibly fall down. Some type of supporting structure would be needed if the stones appeared to be loose.

What I can't tell you is exactly what size of hole in a stone rubble foundation will collapse. This depends on the size of stone (bigger is better), the strength of the mortar (old mortar is quite weak), how tightly the stones are packed in (tighter is better), and even the shape of the stones (jagged is better than round and smooth). I made a hole about 12 inches in diameter and none of the other rocks became loose.

If you are going to cut a hole in a foundation, you work at your own risk. If you aren't sure of yourself, consult a professional.

 

 

Drilling hole in garage wall for 2-inch electrical conduit. Back at the garage:

I drilled a 2½" hole for the electrical conduit. The outside diameter of the 2" PVC electrical conduit is just less than 2½ inches.

 

I tested the fit of the 2" pull elbow. These things are huge, but you need the room for pulling large sizes of wire.

There is a short stub of 2" conduit temporarily stuck in the back side of the elbow.

The hub of the elbow (the female fitting that accepts the conduit) has an outer diameter much bigger than 2½ inches, so the hub won't fit into the hole I've drilled. That isn't a problem.

2-inch pull elbow for new electrical service to garage.

 

New electrical service conduit in trench. We connected the 2" conduit together with PVC cement.

As you can see, this trench is thigh-deep, about 24 to 28 inches deep. Local electrical codes will specify the minimum depth of a buried conduit, so contact your local building department.

 

Since the electrical conduit is governed my the building code, I wanted it to be deeper, so I laid it first.

That white pipe is a 4" light-duty drain pipe that we installed several years ago to divert rain water away from the house.

 

This drain pipe created some problems, because I had to make sure the new 4" pipe didn't collide with it.

If possible the conduits should be sloped to allow water to drain out. If the water puddles in the elbow it could freeze and break the pipe.

Mind you, PVC conduit is supposed to be water-tight, so water intrusion should never be a problem. Sometimes a conduit has to be U-shaped, such as when both ends use pull elbows above ground.

But given the choice, I'd make one end lower, so water could drain out. Just in case.

 

Note the long-radius type of elbow at the lower bend. Pushing cable through this type of elbow is fairly easy... it only creates a small amount of resistance.

There are probably rules that dictate the maximum number of these elbows you can use before you need to employ a pull elbow. With too many curves, you just can't push the wires through, or feed a fishtape through either.

Electrical conduit with pull elbow and long-radius elbow.

 

Partly-filled trench with electrical conduit and special utility conduit. After the electrical conduit was installed, I packed sand around it and created a smooth bed for the 4" PVC pipe.

 

To maintain the ideal level, I supported the other end on some wood blocks while I packed damp sand underneath the pipe. Supporting conduit while packing sand around pipe.

 

Pair of conduits entering garage. The ends of the conduits where they enter the garage.

At the other end, in the basement, we mixed up some mortar and replaced the rocks around the pipes.

I also mixed up some concrete and packed it around the white pipe, both where it broke through the floor and where it exited the wall underground. As I packed the concrete around the pipe outside, I back-filled with sand, which kept the concrete from sagging and falling out of place.

As I back-filled the trench, I tamped the sand with a tamper to make sure it wouldn't settle later.

Later, I added another pull elbow to the electrical conduit, and ran the conduit to a sub-panel.

Since there are no readily-available "junction boxes" for PVC plumbing pipe, I eventually made my own J-box from plywood.

I suppose I could have gone to an electrical supplier and bought some large conduit but I just wanted to use what was available at "Lowe's/Depot".

Conduit with concrete hole patched.

However, I ran into a problem with leaving this conduit open between the house and garage. Even though I stuffed some rags into the hole to prevent cold air from getting into the basement, something managed to crawl in.

 

 

Tools Used:

  • Shovels
  • Basic Carpentry Tools
  • Rotary Hammer
  • Heavy-Duty Drill
  • Hole Saw, 2½"
  • Masonry Tools

Materials Used:

  • PVC electrical conduit and fittings, 2"
  • PVC drain pipe and fittings, 4"
  • PVC cement, primer
  • Concrete bag mix
  • Mortar

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Copyright © 2006 HammerZone.com

Written January 31, 2006