Under 2021 IRC Section R502.8.1, a notch in a solid sawn floor joist may not exceed one-sixth of the joist depth, and a bored hole may not exceed one-third of the depth. Engineered joists and trusses may not be notched or drilled at all unless the manufacturer or a registered design professional allows it.
Notching is cutting a rectangular piece out of the top or bottom edge of a framing member, usually to pass a pipe, duct, or wire or to seat the member on a support. Drilling (boring) is cutting a round hole through the member's depth. Both remove wood where the member carries bending and shear, so the 2021 International Residential Code (IRC) limits how much, how big, and where.
Key facts
- A notch in a sawn lumber joist, rafter, or beam may not exceed one-sixth of the member depth (2021 IRC Section R502.8.1).
- A notch may not be longer than one-third of the member depth and may not be in the middle one-third of the span (2021 IRC Section R502.8.1).
- A notch at the end of a member may not exceed one-fourth of the member depth (2021 IRC Section R502.8.1).
- A bored hole may not exceed one-third of the member depth and must stay at least 2 inches from the top, the bottom, and any other hole (2021 IRC Section R502.8.1).
- Notches and holes in trusses, structural composite lumber, glued-laminated members, cross-laminated timber, and I-joists are prohibited unless the manufacturer or a registered design professional permits them (2021 IRC Section R502.8.2).
- A stud in an exterior or bearing wall may be notched to 25 percent of its depth (2021 IRC Section R602.6).
How much can you notch a floor joist?
You can notch a sawn lumber floor joist to one-sixth of its depth, but only outside the middle third of the span, and the notch may not be longer than one-third of the depth. At the ends of the joist, a notch may go to one-fourth of the depth.
Bending stress in a joist is greatest toward midspan, where the top and bottom edges work hardest, which is why the middle third gets no notch at all. Section R502.8.1 adds that on members 4 inches or more in nominal thickness (beams, for example), the tension side may not be notched except at the ends.
Two practical consequences follow. First, a notch is a fraction of the actual depth, so measure the joist; the code gives no fixed inch value for notches in a floor joist. Second, a notch cut for a bearing seat at the end of a joist is a different case from a plumbing notch partway along it, and the limits differ.
How big a hole can you drill in a floor joist?
You can bore a hole up to one-third of the joist depth in diameter, as long as the edge of the hole is at least 2 inches from the top and bottom of the joist and at least 2 inches from any other hole.
Section R502.8.1 also keeps holes away from notches: where a member is notched, a hole may not be closer than 2 inches to the notch. The code does not restrict hole location along the span in the way it restricts notches, but the 2 inch edge distance means a shallow joist may not have room for a hole at all. Measure the real depth, apply the one-third limit, then check that the 2 inches above and below still fit. If they do not, the hole is not allowed in that member.
Drilling through floor joists for wiring, small pipes, and drain lines is the most common use. The code allows a larger fraction of the depth for a hole (one-third) than for a notch (one-sixth).
What are the limits by member type?
The limits differ for floor joists, rafters, ceiling joists, studs, and top plates because each member carries load differently.
2021 IRC Sections R502.8.1, R802.7.1, R602.6, and R602.6.1: cutting, notching, and boring limits for sawn lumber members.
| Member | Notch limit | Bored hole limit | Source |
|---|---|---|---|
| Floor joist, beam | One-sixth of depth, length not over one-third of depth, none in the middle third of span, one-fourth of depth at the ends | Diameter not over one-third of depth, 2 inches from top, bottom, other holes, and notches | R502.8.1 |
| Rafter, blocking | Same as floor joist, except cantilevered portions of rafters (see below) | Same as floor joist | R802.7.1 |
| Ceiling joist | Same as floor joist, plus taper cuts at the ends not over one-fourth of depth | Same as floor joist | R802.7.1, R802.7.1.2 |
| Stud, exterior wall or bearing partition | 25 percent of stud depth | 60 percent of stud depth, with doubled studs when over 40 percent | R602.6 |
| Stud, nonbearing partition | 40 percent of a single stud depth | 60 percent of stud depth | R602.6 |
| Top plate in exterior or bearing wall | Metal tie required if cut, drilled, or notched by more than 50 percent of the width | Same | R602.6.1 |
Notching rafters and ceiling joists
Section R802.7.1 sends cuts, notches, and holes in solid lumber rafters, ceiling joists, blocking, and beams to Section R502.8.1, so the floor joist limits apply to the roof too. Two exceptions are written into the roof section.
The first is cantilevered rafters. Under Section R802.7.1.1, a notch on the cantilevered portion of a rafter is permitted if the remaining dimension is not less than 3-1/2 inches and the cantilever does not exceed 24 inches. The second is the ceiling joist taper cut: Section R802.7.1.2 limits taper cuts at the ends of a ceiling joist to one-fourth of the member depth.
The most common rafter notch is the birdsmouth, covered with an example in the shed roof framing guide. For sizing the rafter before you cut, see the rafter span chart, and for ceiling joists see the ceiling joist span chart.
How much can you notch or drill a stud?
In an exterior wall or bearing partition, a stud may be notched to 25 percent of its depth. A stud in a nonbearing partition may be notched to 40 percent of a single stud depth (2021 IRC Section R602.6).
Bored holes follow different numbers. The diameter may not exceed 60 percent of the stud depth, the edge of the hole may not be less than 5/8 inch from the edge of the stud, and the hole may not be in the same section as a cut or notch. In exterior walls and bearing partitions, a hole over 40 percent of the depth means the stud must be doubled, and no more than two successive doubled studs may be bored this way. Figures R602.6(1) and R602.6(2) show the conditions; the figure dimensions are not reproduced here, so read them in the code. Stud shoes installed per the manufacturer's instructions are an approved exception.
For stud sizes and spacing, see stud spacing and wall framing basics.
Can you cut or drill a top plate?
Yes, but if piping or ductwork requires cutting, drilling, or notching the top plate of an exterior or interior load-bearing wall by more than 50 percent of its width, you must add a metal tie (2021 IRC Section R602.6.1).
The tie is galvanized steel, not less than 0.054 inch thick (16 gauge) and 1-1/2 inches wide. It is fastened across the plate on each side of the opening with not less than eight 10d nails (0.148 inch diameter, minimum length 1-1/2 inches) at each side, or an equivalent fastening. The tie must extend not less than 6 inches past the opening. The exception: no tie is needed where the entire side of the wall with the notch or cut is covered by wood structural panel sheathing.
Can you notch or drill I-joists, LVL, and trusses?
No, unless the manufacturer's recommendations allow it or a registered design professional has specifically designed for it. This is stated in 2021 IRC Section R502.8.2 for floors and Section R802.7.2 for roofs.
The ban covers trusses, structural composite lumber (such as LVL), structural glued-laminated members, cross-laminated timber, and I-joists. These products have engineered cross sections, such as thin webs, and their holes are limited by manufacturer charts, not by the one-third rule in the sawn lumber section. Do not apply the sawn lumber fractions to them. Use the manufacturer's hole chart and location limits, and call the engineer or supplier if your hole is not on the chart. For roof trusses, see roof truss types.
Do cuts in pressure-treated lumber need treating?
Yes. Field-cut ends, notches, and drilled holes in preservative-treated wood must be treated in the field in accordance with AWPA M4 (2021 IRC Section R317.1.1). The cut exposes untreated wood, so a notch or a bored hole in a treated joist or beam leaves a gap in the preservative envelope until it is treated.
What notching and drilling does not cover
The limits above are prescriptive rules for sawn lumber. They do not replace the following.
- Span and load. A joist that is notched or drilled within the limits still has to meet its span table. See the floor joist span table.
- Lateral support. Cutting a joist does not change the requirement for blocking or bridging. See joist blocking and bridging.
- Adopted code and amendments. The edition your jurisdiction has adopted, plus local amendments, governs. Check with the building department before you cut.
- Engineered products. Use the manufacturer's tables and instructions.
When a pipe or duct would need a notch or hole outside these limits, the usual answers are to move the run, drill smaller holes, use a deeper joist, or frame a soffit or chase. A framing plan that shows the mechanical runs before the joists are ordered avoids field cuts.
Summary
Sawn lumber floor joists, rafters, and beams may be notched to one-sixth of depth (one-fourth at the ends), never in the middle third of the span, and bored to one-third of depth with 2 inches clear at the top, bottom, and any other hole (2021 IRC Sections R502.8.1 and R802.7.1). Studs and top plates have their own percentage limits in Section R602.6 and R602.6.1. Engineered products may not be altered without the manufacturer or a registered design professional (R502.8.2, R802.7.2), and field cuts in treated wood must be treated (R317.1.1).
Framing Plan is a preliminary drawing aid that draws joist layouts, beams, and openings and exports PNG, PDF, and DXF. It does not check notch or hole limits, so verify cuts against the code and your local amendments. Open the framing studio to lay out the joists before you plan the pipe and duct runs.