The plumber needs to run a 2-inch drain through a row of 2x10 floor joists.

Drilling Rules for 2" Drain Through 2x10 Joists (IRC):

1. Location: - Within 2" of joist edge = no drilling allowed. - 2"–1/3 joist depth from edge = max hole size = 1/3 joist depth. - Beyond 1/3 depth = max hole = 4" (but check local codes).

1. Hole Size: - Max diameter: 1/3 of joist depth = 3.06" (for 2x10 = 9.25" actual depth). - 2" drain pipe requires a 2.5" hole (pipe + 0.5" clearance). This is within the 3.06" limit.

1. Spacing: - Min. 2" between holes in the same joist. - Min. 2" from top/bottom of joist to hole edge.

1. Notching (if drilling isn’t possible): - Max notch: 1/4 joist depth (2.31") at edge. - Not allowed in tension zone (bottom of joist).

Key Code Reference: IRC R502.8 (Residential Wood Deck Construction Guide) and R802.7 (Floor Joist Rules) govern drilling/notching. Always verify with local AHJ—some jurisdictions adopt stricter standards.

Recommendation: Drill 3.06" max holes centered in joists, maintaining 2" clearances. If space is tight, consider steel plates or engineered lumber alternatives. When in doubt, consult a structural engineer.

IRC R502.8 (2021/2024) governs notching and boring in sawn lumber joists.

For a 2×10 (actual depth 9¼"):

• Max Hole Diameter: 3⅛" (⅓ joist depth = 3.08", rounded to nearest ⅛").
• Location: Hole centerline must be ≥ 2" from top and bottom edges.
• Clear Zone: You may drill anywhere along the span except the middle ⅓ of the span (where bending stress is highest).
• Spacing: Edge of hole must be ≥ 2" from edge of any notch or other hole.

For your 2" drain (2⅜" OD pipe):

• You need a 2½" to 2¾" hole for clearance/fire caulk.
• This is allowed (2¾" < 3⅛" max).

Critical Checks:

1. Span Location: Verify holes are in the outer ⅓ of the span (near bearing walls/beams), not the center third.
2. Vertical Placement: Center hole 4⅝" to 5⅝" from top (or bottom) of joist. This keeps 2" clearance to both faces.
3. Existing Damage: No notches in the middle third (R502.8.1). No holes in notches.
4. Engineered Joists (I-joists/LVL): Different rules. Follow manufacturer’s hole chart exactly—usually larger holes allowed only in specific zones. Do not guess.

If the plumber wants to notch instead: Max notch depth = ⅙ depth (1⅝") at ends only; no notches in middle third. A 2" pipe won't fit in a legal notch.

Bottom line: Drill 2¾" holes in the outer third of the span, centered vertically. Fire-block penetrations per R302.11. If joists are engineered or span > code tables, stop—call an engineer.