I am running CAT6a wire around my house and I was wondering what the maximum hole size I can drill to run cable across the joists in my basement to various rooms. I should measure but the joists are 2 x 8's I believe.

  • I assume you are talking about conventional dimensional lumber, not engineered beams, such as LVL or I-joists?
    – bib
    Jan 28, 2016 at 13:27
  • yes. They appear to be conventional lumber.
    – salisboss
    Jan 28, 2016 at 13:30

1 Answer 1


According to International Residential Code, the maximum diameter of a bored hole in sawn lumber is 1/3 the depth of the board.

See this answer for more details.

A 2x8 joist has a depth 7¼", so maximum hole diameter would be 2 13/32" (7.25" / 3 = 2.41667").

  • +1 was busy trying to copy illustrations from the res code when I saw your answer. I should have expected that you had us covered.
    – bib
    Jan 28, 2016 at 13:41

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