| 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
Bruce W. Maki,
Editor
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.
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We began by digging a trench between the
house and the garage. |
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| The garage foundation was quite shallow.
The footing (visible just behind the shovel blade) was
only 24 inches below grade. |
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|
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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. |
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| 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. |
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|
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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. |
 |
|
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. |
|
 |
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. |
 |
|
 |
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. |
 |
|
 |
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. |
 |
|
 |
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. |
 |
|
 |
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. |
 |
|
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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. |
 |
|
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.
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|
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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. |
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|
 |
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. |
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|
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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. |
 |
|
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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. |
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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". |
 |
|
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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