Floor I joists

The only portion of the web that can cut to this diameter is in the center of the span, and that would be for one hole, not three. Hole charts provided by the manufacturer are quite specific on this. The three full diameter holes in each the TJI’s have gone far beyond the spec allowances. Followup contractors often do not understand TJI’s and often destroy them when installing their work. Other areas that lack detail are squash blocks in load paths, cut flanges and the improper mixing of TJI’s with dimensional lumber.

We can always agree to disagree, but I will go along with what Curtis Combs has just posted.
Manufacturers recommendations for cut-outs vary on the series of the TJI’s and should be followed to a Tee. Curtis is correct in saying that, virtually, a square hole could be created in fashions that would not impair the structual integrity of the joist. I have done it and seen it. Controled by the Manufacturers recommendations.

Thanks \

Marcel :slight_smile: :slight_smile: :slight_smile:

Hi Marcel,

Under the circumstances as provided by the pictures, and the various views expressed by others… I think this is one of those situations were it may behoove the inspector to advise the client of further need for professional assessment? My reasoning being that an inspector is not likely to know the manufacture, specifications, so forth and so on, while on site. If these are an engineered product, then only a engineer could render the ultimate decision?

Given from what I see those are probably 6" ducts, what size is the joist? Can the web be more than 8"? Doesn’t look that way from the photo.


Hi. Raymond;

I totally agree with you, this scenario is not for a regular Hi"s call.

Marcel :slight_smile: :slight_smile:

Use knockouts
Most I-joists are manufactured with prescored holes that can easily be knocked out with a hammer for the contractor’s convenience in installing plumbing or electrical lines.
Where possible, use knockouts instead of field-cut holes. In floors, framers should place I-joists so the knockouts are at the bottom of the joist, making it easier to install small plumbing lines or electrical wiring. For roofs, the knockouts should be positioned at the top of the joists allowing a flow of air through the system. Knockouts are not technically considered holes and they may be used anywhere on the joist web where they occur.
Precise web cuts.
Field-cut holes should be made with a sharp saw and centered near the middle of the web. As a rule of thumb, the maximum size hole that can be cut into an I-joist web should equal the clear distance between flanges of the I-joist minus 1/4 in. This allows for a minimum of 1/8 in. between the top or bottom of the hole and the adjacent I-joist flange.

Hole location
Holes should only be cut in accordance with the manufacturer’s recommendations. Maximum size holes can typically only be cut near the center of the joist span while only small holes may be cut near the joist bearing. For joists with one or more spans, use the longest span to determine hole location in either span.
Space multiple holes. Where more than one hole in a joist is necessary, the distance between the hole edges should exceed twice the diameter of the largest hole. Each hole must be sized and located in compliance with the manufacturer’s hole chart. Usually, a 1 1/2" hole can be cut anywhere in the web, provided it can be properly spaced from other holes.

Never cut, notch or otherwise modify the top or bottom flange of an I-joist. Cutting the flange will seriously affect the structural integrity of the I-joist. If an I-joist flange is inadvertently cut, contact the manufacturer for recommendations.
By following these product use recommendations and referring to hole charts and installation instructions from the manufacturer, many of the pitfalls to cutting and notching I-joists can be avoided.

I’m not aware of any requirement on limiting the number of holes in an I-Joist, and in fact the APA and I-Joist manufacturers have specific provisions for the spacing/clearances of multiple holes (see the APA guide I referenced, and the TrusJoist specs Raymond posted).

The only limitations usually are the holes must be a certain distance to the ends, must have adequate clearance between holes (typically 2 x diameter), and must have at least 1/8" clear to the top/bottom flanges to make sure they are not cut. Some indicated the holes look way to big as compared to the specs. But keep in mind the web depth (distance between flanges) is about 3" less than the overall joist depth referenced in the specs.

That may have to do with the span of the joists, which rubs me wrong a little … but maybe it’s an optical delusion looking at the pics.

Good call considering the floor was a little bouncy and the holes look marginal.

JMO & 2-nickels … :wink:


Those circles you added to the picture are not correct. The angle of the picture etc. does not allow this method of comparison.

The actual distance between the holes was easily estimated in person as considerably less than 2 x dia.

Hi. Bruce;

Just a short addendum to the subject:

Holes cut in the web area of a wood I-joist affect the
member’s shear capacity. Usually, the larger the hole, the
greater the reduction in shear capacity. For this reason,
holes are generally located in areas where shear stresses
are low. This explains why the largest holes are generally
permitted near mid-span of a member. The required spacing
between holes and from the end of the member is dependent
upon the specific materials and processes used
during manufacturing.
The allowable shear capacity of a wood I-joist at a
hole location is influenced by a number of variables. These
include: percentage of web removed; proximity to a vertical
joint between web segments, the strength of the web
to flange glue joint, flange stiffness, and the shear strength
of the web material. Since wood I-joists are manufactured
using different processes and materials, each producer
should be consulted for the proper web hole design.
The methodology used to analyze the application loads
is important in the evaluation of web holes. All load cases
that will develop the highest shear at the hole location
should be considered. Usually, for members resisting
simple uniform design loads, the loading condition that
develops the highest shear loads in the center area of a
joist span involves partial span loading.
Web holes do contribute somewhat to increased deflection.
The larger the hole the larger the contribution.
Provided there are not too many holes involved, the contribution
is negligible. In most cases, using a producer’s
recommended hole criteria and limiting the number of
holes to three or less per span, the additional deflection
does not warrant consideration.
panel type web, creating the potential for a mismatch in
height as sawn lumber shrinks to achieve equilibrium.
When conventional lumber is used in the vertical orientation,
shrinkage problems are not a problem because
changes in elongation due to moisture changes are minimal.
Hope this helps.
Marcel :slight_smile: :slight_smile: :slight_smile:

The hole on the right does not appear to be round. But this could be the result of the insulative sleeve.

Marcel you raise some interesting points. I still don’t think this I-joist is correct. It would be nice to have a definitive answer.

Hi. rwand;

To be more precise in an answer to this post would require alot more information that the picture this post started with.
In my experience as a Builder of many moons, I would reccommend that the depth of the I-joist be confirmed along with the series, distance in inches between the holes, diameter of the holes, location of the holes in the span of the I-joist, and the span of the joist itself, and also the loading design for it’s intended purpose. All of this factors in to make an educational response that would be accurate, including mine.

As you can see, there are a lot more factors than guessing as to whether or not it is adequate.
At the point where all the relative information has been gathered, contact a structural Engineer related to the Manufactured Product. That should answer all your questions.

Any relative questions or concerns to an Engineered Product, should be addressed to the Manufactures Engineering Department. They will have the correct answer to this Post,
and anything else, is guessing, including my statements, but I actually know where I am comming from. I talk alot off the cuff and probably should not. But, that’s alright. ha. ha.

Hope this helps this post question.

P.S. Raymond, you do have some good post and enjoy reading them. Take care.

Marcel :slight_smile: :slight_smile: :slight_smile:

Hi Marcel,

Absolutely, considering I am in over my head, and only guessing from a photo. But you are right, if in doubt, seek further advice.

How do you feel about the wiring being run through the same holes for the ducts? :wink:


Hi. Raymond;

The proper way would be for the Electrician to use the knockouts provided in the I-joist, and stay away from any other mechanical utilities. Some of the wiring seen in the photo’s that are blue indicates data wiring, and should not be installed or mingled with other utilities in the structure.

Hope this helps.


Just out of interest take a look at the poll results. 47 plus precent think 2-3-4 are the problem. Almost half of the respondents thought there was an issue? Would that mean 47 plus would advise the need for further evaluation? 27 percent said no problem followed by 10 percent who thought there were too many holes.

I wonder what the results would have been if there had not been so many choices.

Next time I will take some measurements and look for the series/type number of the installation.

I am sure 100 percent of one thing, cutouts exceed manuf. specs., the holes are too close together. It was easy to see in person, the picture is at an angle. None of these eng. I- joist allow less than 2 times the diameter between holes. I just reported the other possible problems to my client since it is wrong already.

I have found over the years that when people are given to many choices, the wrong answer or wrong item will be chosen, or in this case the answer that seems to not be wrong.

Give people two choices and the answer would be different.

Almost sounds like trying to get an answer of a Committee of 30 people on a Construction Site to make a dicission. Not going to happen, too many opinions, and we all know that we all have one those. A Committee of three, you have a better chance of getting your input in balance.

Marcel :slight_smile: :slight_smile: :slight_smile:

Good one Marcel. Just under 75% of those voting said something needed evaluation and agreed with Bruce.
I do not often see engineered joists as most of my HI’s are slab on grade. That being said I picked 2,3,4. After the lengthy discussion I would have advised the client to check the manufacturers design specifications and/or consult a Structural Engineer.

I agree with Bruce that the real issue seems to be the clearance between the holes, although it is close. Notice the marks on the first joist where the holes were laid out for cutting … looks like they missed a little on the right … :roll:

Something else rubs me the wrong way about the install … related to the I-Joist span, the pics which seem to show a sag in the middle (optical delusion?), and the reported springy feeling to the floor. This is typically not the result of web holes as the web in the span middle is just holding the flanges in place (doesn’t take much).

It’s possible that the sub-floor was not correctly attached to the I-Joists, which should have the sub-floor glued & screwed/nailed to the top flange to add strength (composite action). An indication of this would be a squeaky floor under the “240 lb load test” … :wink:

Let us know what the results of the follow up evaluation are.

The problem as I see it is the answers (2-3-4) are not the only concerns. The other i-joists also have improper cut outs?
I took the original photo and blew it up. Tell me what you see.


I was speaking to a manufacturer yesterday, hers what he said.
Nearest to the wall you are only allowed a 1/2" hole, but as you move further to the center, depending on the type of truss, there are cases wher you can cut out upt to two feet of the truss, and it will still be a sufficient structural member, capable of the support necessary.

From Tyrone;

there are cases wher you can cut out upt to two feet of the truss

Bingo: Tyrone.