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Guidelines for cutting notches or holes drilled in wood studs to pass wires or plumbing - (C) Carson Dunlop Associates at InspectApedia.com used with permissionCode for Holes or Notches in Joists, Studs, Rafters
Permissible hole size & location in wood framing

  • POST a QUESTION or COMMENT about permissible holes or openings cut into wood framing joist, studs, or rafters in residential construction

Where is it acceptable to cut holes or notches into wood framing members like joists or studs or rafters? Where can those cuts be located and where are they prohibited? How big or deep can we drill, saw, or notch a wood framing member?

This article answers those questions and includes citations to model and adopted building codes that guide builders in drilling or notching these wood framing members.

Page top illustration showing the basic rules for cutting holes in a load-bearing vs. non-load-bearing wood framed wall stud is provided courtesy of Carson Dunlop Associates, a Toronto home inspection, report writing, & education company.

This article series describes wood framing construction, inspection, troubleshooting & repair, including both dimensional lumber (2x's) and also engineered lumber and beams.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Cutting Holes in or Notching Joists, Rafters, Studs, or the Web of Wood I-Joists

Wood I Joist in floor or roofing © Daniel Friedman at InspectApedia.com

Here we discuss guidelines, codes, rules for notching or boring or sawing holes in wood joists.

Best construction practices plan pipe, wiring and duct runs to avoid notching or boring holes in wood framing, particularly in joists and rafters. Our photo shows how one builder did that, by routing ductwork either between or below these web trusses supporting a building floor.

But where such cuts can not be avoided, there are guidelines for the hole or notch location and its size.

If those hole or notch size and location guidelines can't be followed, typically additional framing or reinforcement will be required, ranging from something as simple as doubling a wall stud or ceiling or floor joist to more-complex framing and reinforcement workarounds.

Is It OK to Cut Holes in Floor Joists?

It is oK to cut a hole through the center of a floor joist, provided the hole diameter isn't too large for the depth of the framing member. We give specific hole size rules just below.

First two general rules

Holes or notches in wood framing have rules for size & location

Holes should be in the center of the wood framing member. Notches are allowed in the top or bottom edge of wood joists or rafters, but both of these types of cuts are limited by location in the member and by their size in diameter (for holes) or width and depth (for notches).

Use the actual, not nominal lumber dimensional depth or "D"

Watch out: the D or Depth of wood framing members like joists or rafters, as it should be used in these calculations of allowable hole diameter or notch dimensions, is the actual depth, not the nominal depth.

Example: a nominal 2x10 floor joist is actually 1 1/2 thick and 9 1/4" deep. So the "D" or "Depth" of this member is 9 1/4" (not 10").

As you'll read below, the maximum notch width in a floor joist is D / 3 so for a 2x10 that width is NOT 10/3 or 3.33" but rather it is 9.25 / 3 = 3.08" or as a practical matter, 3 inches, NOT 3 1/3 inches.

See details at DIMENSIONAL LUMBER SIZES

Hole Cutting Locations & Sizes in Wood Studs

In order to preserve the structural capacity of building framing, model codes such as the International Building Code IBC Section 2308 and the International Residential Code, Article R502.8 limit the size and location of holes cut in wood joists. Here is typical wording:

Guidelines for cutting notches or holes drilled in wood studs to pass wires or plumbing - (C) Carson Dunlop Associates at InspectApedia.com used with permission

As Carson Dunlop's illustration shows above, re-states this rule and illustrates it: when cutting or drilling holes in wood studs to pass wires or plumbing, the hole should be centered, and the remaining portion of the wood must be at least 2/3 of the stud depth. If openings larger than this must be cut, the stud will require reinforcement.

Holes Bored in Studs

Hole Cutting Locations & Sizes in Floor Joists & Flat Roof Rafters

Maximum hole size cut in a floor joist:

No structural member should be seriously weakened cutting or notching the member or by otherwise altering the framing member. The Carson Dunlop illustration shows that typical-allowed hole size in a load-bearing wall stud must leave 2/3 of the wood member's depth - or reinforce the member.

Holes Bored in Joists

Unusual Slots, cuts, holes, notches in joists or beams

Wood beam notched to fit abutting top plate of a steel Lally column (C) InspectApedia.com Kahn

Photo: a slot cut into a floor joist to clear the edge of a steel Lally column top plate tell us to be on the lookout for other strange, possibly improper cuts and notches in building framing in this home. Photo courtesy of home inspector DovBer Khan, cited below.

Mr. Kahn writes:

It appears that the beam was cut to support the columns, a construction detail that I've never seen before.

Nor have we.

Our opinion is that if this notch is in the left or right 1/3 of the beam it's probably oK, but as this is a non-standard beam or joist "hole" or slot, its analysis would require help from a licensed structural or civil engineer.

Minimum Hole Size in Studs or Joists

Notch Locations & Size Restrictions in Wood Joists & Flat Roof Rafters

Notches have similar restrictions as the round holes we illustrated just above, with some additional detail that we recap here.

Floor joist notching rules - cited & discussed at InspectApedia.com

In the illlustration above, and referring to the U.S. R502.1.11 [IRC 502.8] Cutting, Drilling and Notching, note that the maximum notch depth is D/6 for members that are less than 4" in nominal dimension.

The notch must be in the 1/3 of ends of the member not in its middle third, and

the maximum notch width is D/3.

Floor Joist Notch Rules

  1. No notches are permitted at all in the center third of a horizontal joist, because cuts there will significantly-weaken the framing member(s).
  2. Notches may be cut in the 1/3 of the horizontal joist length at either end (or both ends) provided that:
  3. The notch horizontal width W is no more than 1/3 of the depth D of the framing member and that:
  4. The notch vertical depth is no greater than 1/6 of the depth D of the framing member

Floor Joist End Notch Rules

  1. Notches cut into a floor joist at its top or bottom either to recess a sill plate above or part of a top plate above, can be no greater in depth than 1/4 the depth D of the framing member.

Ceiling Joists & Flat Roof Rafter Notch Rules

Rules for notches in ceiling joists & rafters - cited & discussed at InspectApedia.com

  1. No notches are permitted in the center third of a horizontal ceiling joist or roof rafter
  2. R 802.7.1 also gives the maximum allowed horizontal distance from a supporting wall or beam, typically 1/6 of the ceiling joist or flat roof rafter length.

End cuts are limited in the allowable depth to joist/rafter depth / 4 as illustrated below.

Rule for depth of allowable end cuts at ceiling joists & rafters - cited & discussed at Inspectapedia.com

Watch out: protection for pipes, wires, or other components routed through notches in some cases through holes in wood framing will usually require extra protection from penetration by nails or screws.

Our photos below show a nail stop plate and nail stops installed to protect condensate drain and refrigerant piping in a wood framed wall where the installer drilled holes through the wall studs to pass those lines.

Nail Stop Simpson Strong Tie NS2 16Ga © D Friedman at InspectApedia.com

See details at NAIL STOPS to PROTECT WIRES

Air conditioning drain line installation © D Friedman at InspectApedia.com

Hole Locations & Sizes in Engineered Wood Beams

Notches, cuts and holes in beams, bearers, joists and rafter members specified within this brochure may have penetrations and notches performed in accordance with AS1684.2, Clause 4.1.6 and the figure below from HySpan, cited below.

Hole location & size guide for cutting holes in engineered wood beams - hySpan cited & discussed at InspectApedia.com

OK to cut holes in the Web of I-Joists

Generally it is permitted to cut round holes in the center of the web of a wood I-joist, depending on the specific guidelines of the I-joist manufacturer.

You should never cut nor notch the top or bottom chord.

The rules for allowable hole size depend on the I-joist dimensions and also on where in the run of the wood I-joist the hole is to be cut. For example, no holes may be permitted near the ends of wood I-joists.

Watch Out: common construction defects involving wood I-Joists include improper size or placement of holes cut in the I-joist web to permit installation of wiring, plumbing, or ductwork.

Improper location or size of holes, notches, or even removal of the center web can cause substantial weakening of the structure and are violations of both the manufacturer's instructions and building codes.

See STRUCTURE, ROOF DEFECTS LIST for details.

Below our photos of I-joists used to support a building floor illustrate how the builder avoided most cuts in the i-joist webs: flex duct and plumbing were laid out to move between I-joists rather than through them, and where an HVAC duct trunk line had to run at right angles to the I-joists the builder suspended it below the I-joists.

This was a much better solution than we found at a different job where the builder removed entire sections of I-joist web to run large rectangular HVAC ducts!

Wood I Joist in floor or roofing © Daniel Friedman at InspectApedia.com

Research & References on Lumber Holes & Notching Codes & Rules

 

 

 


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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2017-03-23 - by (mod) - running air vent ducts requires really big holes cut into joists

James:

Yep as Bernie Campbalik used to say as he'd make a sucking noise thorough his teeth, "They had guys like that back then too."

The return air ducting is particularly critical in that if the air handler is return-air starved the whole system will always be under-performing and operating at unnecessarily-high cost.

Depending on where you live, yes it's common and was permitted to use the space between floor joists as a return air passage - I'd want to be sure that space was clean of insulation, mold, insect debris, etc.

But I'm a little worried about a 4-inch hole through a typical floor joist - even cutting it at the center where it's doing the least harm.

Though it's a different product the concepts are the same as we discuss at CUTTING HOLES in WOOD I-JOIST WEBS [you are on this pagfe] - it's surprising to us beginners that the location of the hole means everything.

On 2017-03-23 by James Thornton

A part of the cold air return has not worked for 60 years. The first Forced Air Furnace ducting install put in, cut off the use of two cold air return vents. One of these vents is the cold air return vent from the second floor, living space.

To use the vents and connect the resulting vent to the rest of the Furnace Cold Air Return would require, say a 4inch hole in the center of the floor joist.

Continued for two joists. I figure I could sister 2 by 4's on the top and bottom and each side of the of the joists, glue and screws, to regain rigidness in the floor joist.

Is this allowed, and advisable. I want to use the joists to become the new extension to the cold air return that I never had.

This Q&A were posted originally

at DUCT ROUTING & SUPPORT

 

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