How to drill a hole through the side of a floor joist

Updated February 21, 2017

Routing electrical cables through floor joists has advantages if a ceiling is planned for a basement or if a subfloor will be laid. Because of the length of a standard drill fitted with a bit, a straight hole cannot be drilled through the joist. Pulling electrical cables will be more difficult and also increase the chance of damage to the cable because of the angled nature of the holes. When drilling holes into the floor joists for the cables, it's best to use a right-angled drill. With the proper tools, you can do the job quickly and accurately.

Anchor the lead end of a chalk line with a tack on the first floor joist if more than one joist is to be drilled. Stretch the line across all subsequent joists.

Pull and release the line to mark the joists. The chalk line provides a visual reference to align each hole with the other.

Remove the chalk line and tack.

Measure 2 inches from the chalk mark toward the centre of the joist. Mark the point with a pencil.

Place a right angle drill fitted with a 1/2-inch brad-point drill bit directly on the 2-inch mark.

Press the point into the wood and hold the drill with both hands so that the bit is at a right angle to the joist.

Drill the hole through the floor joist.


Wear safety glasses. If a larger hole is required, 1-inch auger bits make a smooth hole that makes it easier to pull larger cables or bundles.


Do not drill through laminated wood beams. Cables can be routed over them, but not through them. Check with your local building inspector regarding laminated support beams. Drill floor joist holes away from load-bearing support ends three times the height of the joist. A 12-inch floor joist would require drilling a hole 36 inches from the support point. This distance is only for each hole near a support end.

Things You'll Need

  • Chalk line
  • Tack
  • Measuring tape
  • Pencil
  • Right-angled drill
  • 1/2-inch brad-point wood bit
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About the Author

Max Stout began writing in 2000 and started focusing primarily on non-fiction articles in 2008. Now retired, Stout writes technical articles with a focus on home improvement and maintenance. Previously, he has worked in the vocational trades such as automotive, home construction, residential plumbing and electric, and industrial wire and cable. Max also earned a degree of biblical metaphysician from Trinity Seminars Ministry Academy.