how can a natural knot in a joist be a defect?

Why is this naturally-occuring knot (hole) in a 2x12 floor joist a major structural defect?
knot3.jpg
(my apologies for the image quality)

knot3.jpg

knot3.jpg

Because of the location its weakening the structure much like drilling a hole or notching a floor joist in the wrong place. Proper grading should identify this inferior/flawed lumber.

Heres a few that have failed:

JoistKnot2.jpg

Joist knot1.jpg

As Marcel said.

All lumber is graded, and the grade depends on many variables, such as the number, size, and locatioon of knots; type of cut, type of glue; interior or exterior use, etc.

That knothole would definitely be a structural defect; it should not have been used in that location.

The poor grades are less expensive than the good grades, and many a Weekend Warriior thinks that the lumber is cheaper simply because it has more knots. They don’t understand how knots affect the structural integrity of the lumber.

I can’t tell by looking at the photo if there is a problem? Is this mid-span or near the end of the joist?

Wherever it is, it appears to be too close to the tension area in the bottom of the joist. A hole like that needs to be in the center of the joist, at the neutral axis, in order not to affect the structural integrity of the joist. What may happen is that the joist may crack from the bottom up to the knot, and if it does, then it is effectively a 2x8 or less, not a 2x12, and can continue to fail in a couple of ways: it can crack al the way up, or it can deflect excessively.

I agree.

This will help some:

That was a good reference link Larry,

Thanks

Marcel :slight_smile: :smiley:

A tip of my hat back to you, Marcel, since you furnish so many good references yourself…thank you.:smiley:

Larry,

Great document. Thanks. I haven’t seen that one before.

I encourage you to now watch that document be put in action.](http://http://www.nachi.tv/ppv/5) If this doesn’t blow your socks off - tell me please.

http://www.nachi.tv/ppv/5

How about when found in purlin support?
There is almost 1" deflection on this roof.
Hasn’t failed YET (you’re eligible too)

Barry,

Paige goes over holes in studs (bearing and non-bearing).

** Q: You’re at an inspection, and a non-load-bearing 2x4 stud has a bored hole in it. Its diameter is 1 and 3/4". Is it a defect?**

http://www.nachi.tv/ppv/5

Barry,

if i’m not mistaken, you helped me with this video by answering some questions and providing some pics. Thanks.

You are given credit at the end of the video.
http://www.nachi.tv/ppv/5

Thanks.

Which way is the hole bored through 2x side or 4x side? :mrgreen:

I know the answer to this and my own purlin question, just another pic from last week, timely, imo.

I hope anything I sent was or will be of use. I may have to take the plunge just to find out the “real answer”

Defects in wood sometimes is more than merely a notch or a knot.

Depending on it’s location and use, lumber defects could be critical or have substantial effects on the structural capacities of the Members of the framing network.

Here are a few terms to remember.

Lumber Defects

Defects in lumber are faults which detract from its quality, either in appearance or utility.

Defining various defects is difficult.

**A light or small defect in one piece would often be a medium or large defect in another. **

**In better grades of lumber the defects are light, small or serious depending upon the size of the piece and the way they come in combination with other defects. **

Some common defects may be defined as follows:

A BARK POCKET is a patch of bark partially or wholly enclosed in wood.

A CHECK is a crack in the wood structure of a piece, usually running lengthwise.

A PECK consists of a channeled or pitted area or pocket. Wood tissues between pecky areas remain unaffected in appearance and strength. Peckiness occurs only while the tree is still alive.

DECAY is disintegration of wood fiber. It shows in various stages from barely perceptible to soft and very evident.

ROT and DOTE mean the same as decay.

HEART PITH is the spongy center of the tree which appears on the surface of a piece of lumber.

SHAKE is a crack between and parallel to the rings of annual growth. It produces a defect in the lumber noticeably different from heart pith.

**STAIN is a discoloration that penetrates the wood fiber. It can be any color other than the natural color of the piece in which it is found. **

**It is classed as light, medium or heavy and is generally blue or brown. **

Light stain is often barely perceptible. Think of the minerals that might be drawn into the tree from its water supply in an area where the soil has a heavy concentration of a dark mineral such as iron.

WORMHOLES are caused by insects and beetles. A PIN WORMHOLE is not over 1/4" in diameter. Wormholes bigger than 1/4" are classed as large.

**A KNOT in a piece of sawed lumber is a portion of a branch or limb of the tree. **

A BRANCH KNOT is one that has been sawed at an angle parallel, or nearly parallel to the direction of limb growth.

A SPIKE KNOT is a branch knot that runs to the edge of a piece of lumber, growing larger as it nears the edge.

**A PIN KNOT is one not over 1/2" in diameter. **

**A SMALL KNOT is one between 1/2" and 3/4" in diameter. **

**A MEDIUM KNOT is larger than 3/4" but not over 1 1/2" in diameter. **

**A RED KNOT results from live branch growth in the tree; it is firmly grown into the wood structure. **

**An *INTERGROWN KNOT *is partly or wholy grown together with the fiber of the surrounding wood. **

**A BLACK KNOT results from a dead branch which the wood growth of the tree has surrounded. **

*A*SOUND KNOT is free from decay.

**An UNSOUND KNOT has some decay; it may vary in degree from incipient (just the first traces) to pronounced. **

**An ENCASED or TIGHT knot is one so fixed by growth or position in the wood structure that it firmly retains its place in the piece. **

**A NON-FIRM KNOT, under ordinary conditions, will hold its place in a dry board. Under pressure it can be started but not easily pushed out of the piece. **

A LOOSE KNOT is one that cannot be relied upon to remain in place in the piece.

**PITCH is an accumulation of resinous material. It may be light, medium or heavy, as shown by its color and consistency. **

MASSED PITCH is a clearly defined accumulation of solid pitch.

A PITCH POCKET is a well defined opening in the wood fiber which holds, or has held, pitch.

**A VERY SMALL PITCH POCKET is one not over 1/8" in width and not over 4" in length, or not more than 1/4" in width nor over 2" in length. **

**A MEDIUM PITCH POCKET is one not wider than 1/8" nor longer than 8", or not over 3/8" in width nor over 4" in length. **

In a LARGE PITCH POCKET the width or length exceeds the maximum for a medium pitch pocket.

WANE is the presence of bark or absence of wood on corners of a piece of lumber.

WARP is any variation from a true or plane surface including crook, bow, cup, twist, or any combination of these.

***BOW *and CROOK are similar. Both are deviations from a straight line drawn from one end of the piece of lumber to the other. **
If you were to place a slender board on its thin edge and draw the corners back toward you, this would give you an idea of BOW.
By placing the thin board on its flat side and bending the corners toward you, you get the effect of CROOK.

http://www.bordenanderickson.com/twists.jpg

MANUFACTURING IMPERFECTIONS are those defects that develop during the processing of lumber.

**A ROLLER CHECK is caused when a piece of cupped lumber is flattened as it passes between the planer rollers. **

**TORN GRAIN is a roughened area. **
**This sometimes happens during the surfacing of lumber when the machine tears out bits of wood. **

**A SKIP is an area that the planer failed to surface. In a SLIGHT SKIP the area was not surfaced smooth. **

In a HEAVY SKIP the planer knife did not touch the area at all. A MACHINE BURN is a darkening of the wood due to sticking and overheating of the knives.

**Hope this helps some. **

**Marcel :slight_smile: :smiley: **

Here’s a nice simple “cheat sheet”](http://www.ci.lompoc.ca.us/departments/fire/handouts/cutnotc2.pdf) for those that do Phase inspections

Marcel,

small knot1.jpg

check1.jpg
Paige demonstrates according to the previous definitions… a “sound pin knot” located near a “check.”

:slight_smile: thanks for the definitions - i wish i had them before shooting http://www.nachi.tv/ppv/5

May I ask for your input on the next nachi.tv video? We are shooting a master plumber with 2 hot water tanks on Thursday.

actually i took the liberty to make the knots in the video look bad with a drill bit. :wink:

awesome.

the min. edge distance on that cheat sheet changes when a nm cable passes through

miss paige demonstrating

nm cable hole.jpg

Around here it’s get’er done as I’m sure it is in the rest of the world.

Thats why they created these http://www.strongtie.com/ftp/fliers/F-REPRPROTECT07.pdf

I see these used as much for poor installation (repair) than materials protection as intended.