The short answer: in a load-bearing wall you can notch a stud up to 25% of its depth and bore a hole up to 40%, leaving at least 5/8 inch of wood at the edge and never a hole and a notch in the same spot. In a sawn floor joist, holes max out at one third of the depth and stay 2 inches clear of the edges. Engineered lumber plays by the manufacturer's chart instead — and I-joist flanges never get cut, period.
Why this comes up every September
This is the stretch where buildings get dried in and the mechanical trades stack up behind our crews. Plumbers, electricians, and HVAC installers all show up at once, all looking for a path through the frame, all under the same freeze-up deadline. That's when somebody puts a 3-inch hole through the bottom of a rim joist on a Friday afternoon and nobody says a word until the framing inspection fails.
Studs: the numbers we work to
- Bearing and exterior walls: notch up to 25% of the stud depth, bore up to 40%.
- Non-bearing interior walls: notch up to 40%, bore up to 60%.
- Doubled studs: 60% on the bore is allowed, but not through more than two studs in a row.
- Edge distance: at least 5/8 inch of solid wood between the hole and the face of the stud.
- Never stack them: a bored hole in the same section as a notch turns a stud into a hinge.
On a 2x4 that's roughly a 7/8-inch hole in a bearing wall and an inch and a quarter in a partition — which is exactly why a 3-inch drain does not belong in a 2x4 bearing wall. If the plans put a soil stack in an exterior wall, that wall gets framed 2x6 or the plumbing moves. Catch it at plan review and it costs nothing. Catch it during rough-in and it's a change order.
Top plates get their own rule
Cut or bore more than 50% of the width of a double top plate in a bearing or exterior wall and that plate needs a metal tie strap across the cut — 16 gauge, an inch and a half wide, nailed off on both sides. The top plate is a tension tie holding the building together as a unit. A duct chase punched through it with no strap is a real structural defect, and it's one of the most common things we find.
Floor joists: holes, notches, and the middle third
- Holes: one third of the joist depth max, 2 inches minimum from the top and bottom edges and from any other hole or notch.
- Top or bottom notches: no deeper than one sixth of the depth, no longer than one third, never in the middle third of the span.
- End notches over a bearing point: one quarter of the depth max.
A joist carries bending in its top and bottom fibers and shear near its ends. A hole near mid-span, centered in the depth, does the least damage. A notch on the bottom edge at mid-span does the most — that's where the wood works hardest in tension, and a notch there is a crack looking for a place to start.
Engineered lumber: throw the rules of thumb out
I-joists, LVL, LSL, and glulam do not follow the sawn-lumber numbers. Every manufacturer publishes a hole chart tied to depth, span, and location, and that chart is the only authority.
- I-joist flanges never get cut, drilled, or notched. Not a little. The flanges are the entire load path.
- Web holes go where the chart allows; most I-joists ship with perforated knockouts already located for wire and small pipe.
- LVL and LSL headers and beams get nothing drilled through them without the engineer signing off.
- No member of a truss gets cut for any reason without a repair detail from the truss engineer.
We cover the tradeoffs in engineered lumber vs. dimensional. The field version: if it has a sticker on it, look up the chart before you pick up a hole saw.
How to keep this from becoming a fight
- Frame the chases in. Tell us where the big pipe runs and we build a 2x6 wet wall, a furred chase, or a dropped soffit before anybody drills.
- Walk the frame with the mechanical foremen before rough-in, plan in hand, marking the runs that will be tight.
- Set backing while the walls are open — the same pass we describe in our blocking and backing guide.
- Protect what's drilled. Steel nail plates anywhere pipe or wire runs within an inch and a quarter of the face.
- Photograph overcuts the day you find them, not at the framing inspection.
What happens when it's already cut
Most overcuts are repairable. Sistering a notched joist, strapping a hacked plate, doubling a compromised stud, or in bad cases a flitch plate — normal repairs with normal details. What they are not is a field decision. If the member is engineered or carrying a point load, the repair comes from the engineer of record in writing, and the inspector sees the same paper. We'd rather never get there: frame the chases, walk the rough-in, and the drill never has to go somewhere it shouldn't.
Got a frame with mechanical rough-in stacking up behind it this fall? Send us the plans and we'll coordinate the chases before the first hole gets drilled.