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Notching and boring joists: what it means on an inspection

Rafter Tie editorial teamUpdated 3 min read

Notching and boring are cuts in a joist for pipes, wires and ducts. The rules for sawn lumber control where along the span a notch may go, limit notch depth to a fraction of the joist depth and limit hole size and position. Engineered joists and trusses follow their own rules and are not cut in the field.

A floor joist seen from the side with the parts near the supports and the mid-span marked, small notches near a support, a round hole at mid-span, and labels naming the limits on notch depth, end notches, and hole size and edge distance
The limits are named, not given; read the values for sawn joists in your edition.
Use this diagram

How to check a cut in a joist

  1. Identify the member. Solid sawn lumber follows the code's notching rules. An I-joist or other engineered joist follows the manufacturer's instructions, which usually allow holes only in the web in set locations and forbid cutting the flanges. A truss is never cut without engineering approval.
  2. Find where the cut sits along the span. Bending stress is greatest near mid-span, so the code keeps notches on the top or bottom edge out of the middle part of the span. Read the exact zone in your edition.
  3. Measure notch depth. The code limits a notch on the top or bottom edge to a fraction of the joist depth, and sets a separate limit for a notch at the end where the joist bears. Check the depth and length limits in your edition.
  4. Measure holes. The code limits a bored hole to a fraction of the joist depth and sets a minimum distance from the top and bottom edges.
  5. Count the cuts. The limits apply to each cut and to the combination. Several holes close together, or a notch and a hole in the same spot, weaken the member more than either alone.

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Common mix-ups

  • Notch versus bore. A notch removes material from an edge. A bored hole removes material from inside the member. The limits differ.
  • Floor joists versus studs. Wall studs have their own limits in the wall framing section of Chapter 6. Do not carry joist numbers over to studs.
  • Edge distance is from the edge of the hole. The minimum distance is measured to the edge of the hole, not to its center.
  • Plumbing convenience is not a code basis. A cut that is easier for the trades does not make it allowed.

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Joist cuts on the B1

These cuts are part of floor construction, 14% of the B1, and the numbers are the kind that tests turn into a measurement question. The sawn-lumber limits are in Chapter 5, where cutting and boring of joists is covered; the limits are named above but not given, so read them in your edition and tab the section so you can find it in under a minute.

Practice it

Build the habit of finding the section fast with the code navigation drill. Then read band joist, the member at the edge of the floor that also takes trade cuts, and bearing wall versus non-bearing wall, which affects stud cuts in walls. The IRC terms glossary has the rest.

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