How to drill plumbing holes for tji floor joists

Written by paul massey
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TJI floor joists are a manufactured "I" joist widely used in residential and light commercial construction as a pre-engineered replacement for common dimension lumber. Once the TJI floor joists have been installed, the plumbing supply and drain lines can be run within the joist space. Cutting the needed holes is a simple procedure.

Skill level:
Moderately Easy

Things you need

  • Tape measure
  • Compass
  • Electric drill
  • 3/8- or 1/2-inch wood bit
  • Jigsaw or reciprocating saw

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  1. 1

    Mark the centre point of the desired plumbing hole on the side surface of the TJI floor joist's vertical web. Refer to the manufacturer's specifications to ensure compliance with the structural limitations regarding cutting and penetration of the joists.

  2. 2

    Scribe the outside diameter of the hole using a compass. Measure the outside diameter of the plumbing piping and add approximately 3/8 inch to determine the diameter of the hole.

  3. 3

    Drill a 3/8- or 1/2-inch hole at opposing sides of the hole's diameter just inside the scribed line using an electric drill with a wood boring bit.

  4. 4

    Cut out the plumbing hole in the TJI floor joist using a jigsaw or reciprocating saw.

Tips and warnings

  • The flanged opening of an appropriately sized ABS fitting can also be used to scribe the outline of the hole diameter.
  • The manufacturer of TJI framing components recommends specific size and location limitations for drilling holes in TJI floor joists. These specifications should be consulted to ensure proper placement and minimal effect on the structural integrity of the joist.

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