See also Notching & Boring Studs
Tradespeople often need to cut notches or holes in floor and ceiling joists to run pipes, ductwork, or wires. Sometimes joists are notched at the end where they bear on a wall or sill. If the cut-outs are too large or in the wrong location, the joist can be weakened and unable to support the load it was designed for. These joists may need reinforcing to reduce bounciness, sagging, or excessive deflection in the floor or ceiling.
The illustration and table below shows where cuts are permitted and the maximum size allowed, based on D, the depth of the joist (top to bottom) in inches. For example, a hole should not be greater than 3 in. in diameter if the joist measures 9 in. deep, the approximate size of a 2×10 after normal shrinkage.
Click here to download a full notching and boring guide for joists and studs from the WWPA.
In general, never make notches in the middle third of the joist, where the bending forces are greatest. Other rules, in compliance with the International Residential Code (IRC R502.8 and R802.7) are:
- Don’t make any holes with a diameter greater than 1/3 the depth of a joist.
- No holes closer than 2 inches to the top or bottom edge.
- No holes closer than 2 inches to any other hole or notch.
- No notches in the middle 1/3 of the joist, but holes are permitted here.
- No notches deeper than 1/6 the joist depth.
- No end notches (where the joist is supported) greater than 1/4 the joist depth.
- The length of a notch should not exceed 1/3 the joist depth.
- Do not make square or rectangular cutouts. Also avoid square cuts in notches — angled cuts are better, as shown. Square cuts tend to start cracks.
- No notches are allowed in the top of a large beam (greater than 4 in. thick), except at the ends.
Read more on Fixing Bouncy & Sagging Floors
Read rules for Notching & Drilling Studs
ROBERT ARTIS says
Notching & Drilling Guide for Studs?
What size hole can I put in a 2×4 wall, starting on one end of the wall?
buildingadvisor says
The IRC rules for notching and boring stud is pretty straightforward, and summarized in the diagram below from The WWPA.
In loadbearing and exterior-wall studs:
• Notch depth can be up to 25% the width of the stud. No maximum notch length in specified.
• Hole diameter can be up to 40% the width of the stud and should be a minimum of 5/8 inch from the edge.
• You may drill holes up to 60% the stud width as long as the studs are doubled and you don’t drill through more than two doubled studs in succession
In non-loadbearing studs:
• Notch depth can be up to 40% the width of the stud
• Hole diameter can be up to 60% the width of the stud.
In all cases, holes and notches must not line up (horizontally) with any other holes, notches, or cuts in the stud.
When in doubt, it never hurts to nail a length of 1½ -inch-wide steel strapping (16 ga.) over the drilled or notched section of the stud for reinforcement. This is required for any top plate notched or drilled more than 50% of the its width.
You can find more detail at thi
Art Brad says
Hi, I’m renovating my basement, It helps me a lot, if I notch one joist thats seats above a wall. (The whole length is above the wall. Need a big noch to pas trough air intake) The joist are 2×8.
Im I allowed to?
buildingadvisor says
The rules described above, based on IRC 502.8, apply equally to “notches [and holes] in solid lumber joists, rafters and beams.” Rafter spans are measured horizontally, not along the length of the rafter — but the middle third is same measured either way.
Bob says
What Are Rules For Drilling & Notching Rafters?
My house has a hip roof and I am looking to finish the attic. Currently it is not vented and I am going to tear down the old insulation, install baffles and put up new insulation. My question is how large of a hole can I drill in the 2×6 jack joists so air can circulate up to the ridge? Thanks
buildingadvisor says
Boring and notching of rafters follow the same IRC rules provided for joists, as described in the article above. One difference with rafters is that no holes are allowed in the cantilevered rafter tails, but the tails can be notched along the bottom as long as 3-1/2 in. of wood remains.
In the language of the IRC (International Residential Code):
How much airflow you get through these holes in the jack rafters is another question. While the code does not specify the location of the air vents, it’s widely accepted that about half the ventilation area should consist of low intake vents and half high exhaust vents. Some experts like to see more low vents (60 to 66%) than high. If you have a horizontal section of ridge, use a high-capacity ridge vent. If the roof comes to a point or you have a very short ridge, you will need to add mushroom vents or other in-field vents to provide enough exhaust ventilation.
Another option is to use a product like the Shingle-Over Hip Ridge Vent, from ShingleVent or the Cobra Hip Vent from GAF. When installing these, follow the manufacturer’s instructions for cutting ventilation slots in the sheathing on either side of the hip rafter. No drilling of the jack rafters is needed but could be used to enhance the ventilation.
Darrell Smith says
Thanks for the great information! I’m finishing an existing storage area. If I notch a floor joist (within the guidelines) to ‘bury’ previously installed electric cables, does the code define how those notches should be covered, to avoid drilling or nailing into them if framing over top? I’ve used metal plates in the past, but not sure that’s up to code.
buildingadvisor says
Sounds like you’ve been doing the right thing all along, so you’re good to go. For wiring not in metal or non-metal conduit, The 2020 NEC states:
“Where there is no objection because of weakening the building structure, in both exposed and concealed locations, cables or raceways shall be permitted to be laid in notches in wood studs, joists, rafters, or other wood members where the cable or raceway at those points is protected against nails or screws by a steel plate at least 1.6 mm (1/16 in.) thick, and of appropriate length and width, installed to cover the area of the wiring. The steel plate shall be installed before the building finish is applied.”
Steve says
Maximum Length of Notch at Joist Ends?
I’m redoing an old farmhouse. I’m sistering and replacing about 16 joists, which are in bad shape since the back end of the house took on a lot of moisture.
The structural engineer left off the code information, but he said to notch the ends to fit the rim. The current joists from the 1800s are 2x7s. I can fit new pressure-treated 2x8s. According to this page and the engineer, I can notch the ends to fit the rim joist. The only thing I can’t verify is how long the notch can be if I notch the bottom end of the joist at the code depth. There is some space between the rim and the start of the foundation.
Thanks
buildingadvisor says
Good question. The building codes (IRC and regional codes) do not specifically address the maximum length of the notches at the ends of the joist. However, it’s clear that a very long notch will undermine the strength of the joist. But how long is too long?
The issue is addressed in the 1991 National Design Specification, which limits the length of the notch to 1/3 the depth of the joist. For a nominal 2×8 joist, that’s about 2-1/2 inches. That is probably a conservative number, but if you need to exceed it you may want to check with your engineer.
Also, please note that you can reduce the stress at the notch by cutting the vertical side of notch at about 45 degrees, as shown. Otherwise the corner of this and other square-cut notches are prone to cracking at the corner.
Rob Brassard says
Can I Notch & Drill Joists Under Ceramic Tile
Thanks for the info and graphic. I’m currently remodeling a floor and sistering 16′ 2×10’s to existing nominal 2×10’s across an open span. I’m adding 2×10 blocking in at least 2 rows. The new spacing will be a little less than 15″ OC. This floor will support a 3/4 OSB floor, ditra, and a tiled bathroom. How do these recommendations apply with the extra joists?
buildingadvisor says
Ceramic tile is an inflexible material that requires a very stiff subfloor to prevent cracking of the tile and grout.
To avoid problems, tile installations require a maximum deflection of L/360 in both directions: along the joists (a function mainly of joist depth) and between the joists (a function of the subflooring). Not sure what wood species you are using, but a typical #2 SPF 2×10, spaced 16 in., can span up to 15ft.- 5 in. at L/360. So doubling the joists will make an even stiffer floor.
With tile, the deflection the across the joists is often more of a problem than along the joists.
While the tile industry has not specifically endorsed OSB as an subflooring, it is widely used. They specifically recommend against bonding tile directly to the OSB, not a problem in your case. For tile, the plywood subflooring with 16-in on-center framing, should be minimum 5/8 in., or ¾ in. if it’s OSB. Upgrading 5/8-in. plywood to ¾ in. will stiffen the floor as much as 80%. Gluing and screwing the underlayment also helps stiffen the floor.
By sistering all the joists and adding solid blocking, you are further stiffening the floor. When you start cutting and notching, however, you begin the weaken the floor. I would still try to follow the notching and boring recommendations in the chart. Remember, these rules of thumb are were developed for standard house framing and finishes, not the special needs of ceramic tile.
If you need to go beyond what is allowed in the chart, you may need additional support – for example, by gluing and screwing plywood to the underside (and topside of the joists), creating a very stiff box beam. If you really want to push it to the limit, I’d suggest having an engineer take a look.
Read more on Ceramic Tile Flooring
Matthew H Krohn says
Can I Make A Shallow Notch Longer?
Can you go longer than recommended if the notch is shallower? I have a clearance issue and would like to cut a notch 13.5 in. long and 5/8 in. with an angled end in a 12 in. joist about 3 feet from the support. I have not been able to find anything about long, shallow notches.
buildingadvisor says
Rules of thumb like this tend to be conservative and assume a worst-case scenario, such as a notch in every joist. They also assume that the joist is maxed out in terms of span and load. For example, maybe the joist size could span from 10 to 14 feet and your span is only 11 ft. So the 5/8 in. notch still leaves you plenty of wood. You could check a span table to find out, or use an online span calculator.
I wouldn’t be overly concerned about a 5/8 in. notch in a 12 in. joist. But it’s not clear whether you are notching just one joist or many. Also, it’s not clear if you are notching in the outer third of the span as allowed. Also, how much stiffness you need depends on your finish flooring. I’d be more concerned with ceramic tile than with hardwood.
If you are just notching one or two joists, and want to add a little extra support, you can add solid bridging to the full joists on either side of the notched joist. The bridging can be staggered to allow end nailing with 16d nails – three in each end.
You can also strengthen a weakened joist by gluing and screwing the subflooring that crosses the notched joist. If accessible, you can add the plywood below the joists as well, forming a structural box beam.
If one or more joists are significantly undersized due to notching, you can strengthen them by sistering a joist or flitch beam (ry) alongside the notched joists. Depending on space and the support needed, you can use 2x lumber or thick plywood, or if necessary, even LVL or steel.
If you’re not sure, have a structural engineer take a look. Each situation is different and he should be able to quickly suggest a simple solution. With such a shallow notch, your biggest concern might be a soggy section of subflooring.
You can read more on these strengthening weak joists in my post on fixing bouncy floors
Austin Locklin says
Can You Drill 2×4 Joist?
I see it says “none” in your table, for the 2×4 row. Does this mean there should be no holes drilled in a 2×4 floor joist or ceiling rafter?
buildingadvisor says
Yes, the code does not allow drilled holes or notches in 2×4 joist or rafters. You rarely see 2×4 rafters or joists except in garages, sheds, or other outbuildings.
That said, you could probably get away with drilling a few small holes in the center of a 2×4 rafter/joist that is properly sized. A better approach, and one allowable by code, would be to run the wires or pipes on the underside of the 2x4s and then use furring, 2x3s, or similar to “fur down” the framing before installing the ceiling.
Where a wire passed over the framing, place a metal electrical box cover over the wire to protect it from nails, as required by code. It’s a good idea to do this for copper or plastic piping as well.
brandon says
Are Holes In Rafters Allowed?
I have 2×8 rafters for my ceiling. (roof) can i put holes in them to run electrical. Will be getting it inspected
Eddie Marano says
How Many Holes Can I Drill in a Floor Joist?
Hope everyone is safe and well.
Thanks for this! I do have a question that isn’t addressed by your article (though common sense might have the answer): how many holes can be bored into a 2×8″ joists side by side (with the 2″ space allotted) and I guess same question for notches.
The problem I have is that a cold air return from a bedroom goes nowhere because they cut the return one joist bay away from the return ducting going to the furnace and there is a joist blocking the path. Thanks
buildingadvisor says
The code places no specific limit on the number of holes you can drill in a joist, as long as you follow all the rules stated in the article above.
The minimum distance between holes, or between a hole and notch measured horizontally, is 2 in. A more conservative rule of thumb preferred by some builders is to use the maximum hole size (where it is greater than 2 in.) as the minimum distance between holes. For example, in a 2×10 joist, the minimum distance between holes or from a hole to a notch would be 3 in. In your 2×8 joists, the minimum distance between holes would be 2-3/8 in.
So in theory at least, you could drill holes from one end of a joist to the other, spaced apart by 2 in., although I wouldn’t recommend this. I’d also avoid drilling or notching close to a large knot. It’s important to follow the rules, but use common sense as well, as you suggest.