How to Run Conduit Under a Slab

Written by don davis
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How to Run Conduit Under a Slab
Conduit should be routed under concrete slabs before pouring the concrete. (Polka Dot Images/Polka Dot/Getty Images)

A conduit is a metallic or nonmetallic pipe that insulates gas and electrical lines underground. It is theoretically possible to bore a hole through the substratum under an existing concrete slab but it would be cheaper to pour a whole new slab. It is also possible to dig a tunnel under slab and lay the conduit in that but it is impossible to properly backfill the tunnel. The correct way to lay conduit under a concrete slab is before the slab is there. The only feasible way to run conduit under an existing slab is to partially demolish the slab.

Skill level:
Moderately Challenging

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Things you need

  • Indelible marker
  • Steel measuring tape
  • Concrete saw
  • Sledge hammer or jack hammer
  • Hacksaw
  • 5/8-inch-diameter reinforcing bars
  • Bricks
  • Rebar wire
  • Rebar wire tool
  • Fresh concrete

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  1. 1

    Mark the route of your conduit on the concrete slab with an indelible marker.

  2. 2

    Measure 6 inches to the left and right of both ends of the marker line with a steel measuring tape.

  3. 3

    Connect the two marks to the left of your conduit route with the steel measuring tape. Using the measuring tape as a ruler, mark a straight line between the two marks with the indelible marker.

  4. 4

    Connect the two marks to the right of your conduit route with the steel tape and mark a straight line between those marks with the indelible marker.

  5. 5

    Saw through the concrete slab with a concrete saw using the indelible lines as a guide.

  6. 6

    Break all the concrete in the detached portion of the slab with a sledge hammer or a jack hammer. Remove and discard the concrete pieces.

  7. 7

    Saw any remaining steel reinforcing bars integral to the slab with a hacksaw to completely open a 1-foot-wide breech through the slab. Remove all reinforcing bars from the breach.

  8. 8

    Dig a 24-inch-deep trench through the length of the breach in the concrete slab using a shovel. Measure the depth of the trench with a steel measuring tape. National code requires conduit to be buried 18 inches to 24 inches deep. Conduits under roads, car parks and driveways should be buried 24 inches deep.

  9. 9

    Lay the conduit on the bottom of the trench. Backfill the trench with dirt using a shovel.

  10. 10

    Lay 5/8-inch-diameter reinforcing bars in the breech. Lay the reinforcing bars on top of bricks in the trench. If necessary, the bars should be shortened with a hacksaw so they do not extend closer than 4 inches from each end of the breach. If the breech is longer than 20 feet, overlap two or more reinforcing bars to span the length of the breech in the slab. Overlap reinforcing bars by at least 2 feet.

  11. 11

    Tie overlapping reinforcing bars together with rebar wire using a rebar wire tool. Refill the breech in the slab with fresh concrete and refinish the slab.

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