Notching and Boring Limits in Wood Framing

Why this matters

A joist or stud that has been over-bored does not fail on the day. It deflects a little more under load, then a little more, and a year later the tile cracks, the door binds, or an inspector on a remodel finds a run of oversized holes with your shop's pipe in them. The limits are short, published, and the same in most of the country, and almost every structural callback from a trade that is not a framer comes from not knowing them.

This card owns those limits for sawn lumber: floor and ceiling joists, rafters, studs and top plates. It states them as the International Residential Code sets them in the 2021 edition, which is the edition most states have adopted or are moving to. The numbering moved between editions (the joist section was R502.8 for years, with the lumber rules in R502.8.1), so check your own jurisdiction's adopted edition and any local amendments before you rely on a section number. The numbers themselves have been stable for decades.

First, is it sawn lumber

Every limit on this card applies only to solid sawn lumber. I-joists, LVL, glulam, parallel-strand beams and trusses are excluded: the IRC (R502.8.2 in the 2021 edition) prohibits cuts, notches and holes in engineered wood products except where the manufacturer permits them or a registered design professional designs them. A sawn-lumber rule applied to an engineered member is not a conservative approximation, it is the wrong rule. See related: Engineered I-Joists and the Hole Chart, and LVL, Glulam and Beams You Never Drill Without Approval.

Field cue: sawn lumber has a grade stamp with a species and grade and is one solid piece through its depth. An I-joist has flanges and a thin web. LVL shows thin veneer layers on its edge. Glulam shows stacked laminations on its side. A truss is a triangle of members joined by metal plates.

Joists and rafters: what the beam is doing

A joist under load bends. The top edge is squeezed (compression), the bottom edge is stretched (tension), and the middle of the depth, the neutral axis, carries little bending stress but carries the shear that peaks near the supports. Bending stress is highest in the middle of the span. Those two facts are the entire logic of the limits:

• Notches remove wood from an edge, where bending stress lives, so they are kept small and kept out of the middle of the span, where bending is worst.
• Holes remove wood from the middle of the depth, where bending stress is low, so they are allowed to be larger, but they must stay off both edges.

The IRC limits for sawn joists, rafters, blocking and beams, as adopted:

The member depth is the actual dressed depth, not the nominal size: a 2x10 is 9-1/4 in, a 2x8 is 7-1/4 in, a 2x12 is 11-1/4 in. Using nominal depth inflates every allowance by about 8 to 10 percent, in the unsafe direction. The code also forbids notching the tension (bottom) side of members 4 in nominal or thicker except at the ends.

Here is what those rules leave on a 2x10 over a 12 ft span:

SIDE VIEW, 2x10 JOIST (9-1/4 in deep), 12 ft SPAN

   bearing                                  bearing
   v                                              v
   +----------------------------------------------+
   |  no hole within 2 in of the top edge         |
   |  holes OK     |  holes OK    |  holes OK     |
   |  notch OK     |  NO NOTCHES  |  notch OK     |
   |  no hole within 2 in of the bottom edge      |
   +----------------------------------------------+
   |<--- 4 ft ---->|<--- 4 ft --->|<--- 4 ft ---->|
      end third     middle third     end third

hole:  3 in dia max (1/3 of 9-1/4 = 3-1/16)
notch: 1-1/2 in deep max (1/6 of 9-1/4 is 1.54)
       3 in long max (1/3 of the depth)
end notch at the bearing: 2-1/4 in deep max (1/4)

The figures under the drawing are rounded down to the nearest practical fraction, which is the direction to round.

Rafters and ceiling joists carry the same rules in the roof framing chapter (R802.7.1 in the 2021 edition), with one practical difference: the bird's-mouth cut at the bearing is part of the rafter design. Do not deepen one to drop a rafter onto a new plate; a deeper seat cut is a design question, not a field fix.

Studs: bearing or not

Studs are columns, not beams. They carry load along their length, and what limits them is buckling. The IRC (R602.6 in the 2021 edition) sets two sets of numbers, and which applies depends on what the wall carries:

For every bored hole, the edge of the hole must stay at least 5/8 in from the edge of the stud, and the hole may not be in the same section of the stud as a notch. Width here is the stud's depth through the wall: 3-1/2 in for a 2x4, 5-1/2 in for a 2x6.

Every exterior wall counts as bearing for this table whether or not it carries a floor above, because it carries wind. If you cannot tell whether an interior wall is bearing, treat it as bearing. A wall that runs perpendicular to the joists above it, near mid-span, or that lines up with a beam or wall on the floor below, is very likely bearing.

Top plates: the 50 percent rule

The double top plate ties a wall together along its length and carries the joists or rafters above. Where piping or ductwork requires cutting, drilling or notching the top plate of an exterior wall or interior bearing wall by more than 50 percent of its width, the IRC (R602.6.1 in the 2021 edition) requires a galvanized steel strap across the opening: not less than 0.054 in thick (16 gauge) and 1-1/2 in wide, fastened to the plate on each side with not less than eight 10d nails, extending at least 6 in past the opening. The exception is where the whole side of the wall at the cut is covered by wood structural panel sheathing. See related: How to Drill a Top Plate and Restore It, which owns the strap installation.

A worked example: one bathroom, three framing calls

A plumber is roughing a new second-floor bath. The drain is 3 in PVC (outside diameter 3-1/2 in, so the hole needs to be about 3-3/4 in). The vent is 2 in PVC (outside diameter 2-3/8 in, hole about 2-1/2 in). The floor is 2x10 joists at 16 in on center on a 13 ft 6 in span, and the wet wall is an interior bearing wall.

Call one: the drain through the joists. The 3 in drain must run 6 ft perpendicular to the joists to reach the stack. A 2x10 allows a hole of 9-1/4 divided by 3, which is 3.08 in. The drain needs 3-3/4 in. That is 0.67 in over the limit, so no joist may be bored for this pipe anywhere along its length. The two options are routing the drain parallel to the joists inside one bay to a stack location on the same line, or dropping it below the joists inside a soffit in the ceiling below. The plumber moves the toilet 10 in so the drain runs parallel inside one bay, and no joist is cut. Had the floor been 2x12, the limit would be 11-1/4 divided by 3, or 3-3/4 in, exactly the hole needed, centered with 3-3/4 in of wood above and below, more than the 2 in edge rule. That is legal but leaves no room for a sloppy bit, and the drain has to slope at 1/4 in per foot, so the holes climb as they go and the edge rule has to hold at every joist, not just the first.

Call two: the vent through the wall plates and studs. The wet wall was framed in 2x4. A 2-1/2 in hole in a 3-1/2 in stud is 2.5 divided by 3.5, about 71 percent, which exceeds even the 60 percent limit for a doubled stud in a bearing wall. No stud in a 2x4 bearing wall can take this vent. The framer reframes the wet wall section in 2x6, where 2.5 divided by 5.5 is about 45 percent: over 40, under 60, so each stud the vent passes through is doubled, and no more than two successive doubled studs are bored. Centered, the hole leaves 1-1/2 in on each side, more than the 5/8 in edge distance.

Call three: the vent through the top plate. The vent exits the wall going up through the double top plate. A 2-1/2 in hole in a 5-1/2 in plate is about 45 percent, under 50, so no strap is required by the code. But the drain stack below, if it had gone up through the 2x4 section, would have taken 3-3/4 in out of 3-1/2 in of plate, which is the whole plate and more, and would need the strap on both sides of the opening.

And the protection the holes now need. Each hole lands at least 1-1/4 in from the stud face on both sides, which keeps the pipe clear of drywall screws; where a pipe in a hole or notch sits closer than that to the edge, the plumbing chapter (P2603.2.1 in the 2021 edition) requires a steel shield plate. See related: Nail Plates and Protecting What Runs Through Studs.

What changes the answer

A joist carrying more than its neighbors. A joist under a bearing wall above, under a tub, or doubled at an opening is already working harder than the table assumes. The table is a prescriptive limit for a typically loaded member, not a promise that every joist can lose that much wood. Leave the doubled and heavily loaded members alone and move the hole.

Damage or prior cuts. A joist already notched by an earlier trade, split, or with a large knot at the planned hole has less capacity than the rule assumes. The limits do not add up: a hole that is legal in a clean joist next to a notch that is legal on its own may be within 2 in of it, which the table forbids.

Anything over the line. Once a hole or notch you need exceeds the table, the answer is not a little reinforcement by eye. It is a different route, or a repair designed by an engineer, and the engineer needs the member size, span, spacing, what sits above, and the cut you want with its location measured from the bearing.

References

• International Residential Code, 2021 edition, R502.8 (floor framing drilling and notching), R602.6 and R602.6.1 (studs and top plates), R802.7.1 (roof framing), P2603.2.1 (pipe protection), as adopted by your jurisdiction
• See related: Before You Cut: The Four Things a Hole Can Break
• See related: How to Drill a Top Plate and Restore It
• See related: The Sagging Floor That Started With a Drain Line
• See related: The Structural Cut Approval SOP