I’m in the process of redoing a bathroom and it has been stripped down to the studs and floor joists. Some of the joists had been notched on top and whatever the notches provided clearance for is no longer there.
I have sistered new joists where needed and was wondering if there is any advantage to filling in the notches?
The top of the joist is in compression when a force is applied and if the notch is filled in with a “dutchman” would that restore any strength?
I assume it will never be “good as new”, but if I glue and force fit in some patches will it help or is a waste of time? I was thinking it would transfer the compressive force along the top of the joist instead of an inch or so down. I was always under the impression that if you notch 2″ out of the top of a 10″ joist you now have the span capacity of an 8″ joist – is that true? And if so would filling the notch return it a 10″ capacity?
Thanks.
Replies
The top of the joist is in compression when a force is applied and if the notch is filled in with a "dutchman" would that restore any strength?
Not sure what this sentence means and I dont know what a "dutchman" is but I'll give you my $.02 anyway.
The code book says you can have a notch in your joist 1/3rd of the depth of the joist and still be ok AS LONG AS that notch is not in the middle 1/3rd of the joist.
So if you have 2x10 12' long. You can have a notch, or hole, 3" deep and still be good as long as that notch is in the first 4' or the last 4'.
If I had any real concerns about the joist not holding up over time I would rip a pece of OSB or plywood 9" and glue and nail it to the side of the joist.
Hope that helps.
A "dutchman" is a piece of wood cut to fit in an existing opening, ie filling a hinge mortise, or in this case a notch in the joist"Shawdow boxing the appoclipse and wandering the land"
Wier/Barlow
scabbing plywood alongside a notch means you are relying on the shear strength of the nails in wood to handle things. adding glue would help.to explain his statement on compression - when a joist defelcts down from vertical load, the fibres in the top of the joist are in compression laterally, the same way a post is when under load. The fibres in the bottom of the joist are under a tension - trying to stretch apart laterally as it deflects downwards. A notch there would be harder to deal with
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lateral is side to side
your talking long axis = longitudally?No Tag
Yeah - same thing - I'm taking my reference point from the house not the individual member when I say that.
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now I am with youNo Tag
Thanks.Nails have some serious sheer strength. It seems any time I involve an engineer in a situation like this their response is plywood, glue and nails. Always something ridiculous like 4 nails every 4" on center. This leads me to believe that plywood is the new duct tape.
Leaky furnace? Plywood it. Glue and nails
Sump pump stuck on? Plywood it.
4 nails every 4" into an old dry 10" joist?Seems like that could cause some splitting if not careful.There is such a thing as too many nails and too closely spaced. Around here, that tight of nailing pattern is called "fire proofing"DC
Thanks for the info. I did sister onto each affected joist using 3/4" plywood, glued, clamped and nailed. I used a bunch of nails (not 4" on center, though) and I assume that the glue - I used Titebond 2 - would do most of the work.
I did fill the notches with 2x material, glued (not nailed) in place. Of course, since the house is old, the existing joists were closer to true 2" thickness than my patches. I am sort of an overkill type of person so I figured it couldn't hurt.
I'll let you know if I end up with cracked tiles. Just kidding, the joist span is only 8ft and they are no more than 16" oc with some even closer than that. I also added some blocking where I felt it was needed so the joists shouldn't "roll" under deflection. I am probably using some 12" square floor tiles and don't want them to move.
Thanks.
Everybody, Hasn't anyone heard of Simpson SDS screws? They are mostly used in heavy duty hold downs. Their shear strength is considerably stronger than the loads subjected to the wood. Many codes accept them for joining two or more pieces of lumber together. I probably used a couple of thousand of them on my last big commercial remodel of a very old building. They go in very nicely with a cordless impact. Since you state that the span is only eight feet, you're probably just fine. With ceramic floor tile though, you want absolute rigidity. Just make sure that your floor substrate will not flex. Two layers glued and nailed with ring shank nails would be good. Stand in the middle of the floor and put your weight to work on the floor-you shouldn't feel almost any flexing.
'The code book says you can have a notch in your joist 1/3rd of the depth of the joist and still be ok AS LONG AS that notch is not in the middle 1/3rd of the joist.'
'So if you have 2x10 12' long. You can have a notch, or hole, 3" deep and still be good as long as that notch is in the first 4' or the last 4'.'
Not trying to be argumentative, but are you sure about notches? Drilling maybe, but notches???
I have always understood that the cutting of the top and bottom chord of any joist was verboten under penalty of Building inspector purgatory.
S Crough,Yes I am sure that notching is allowed. I've had to photocopy that page many times and give it to the plumber/HVAC and electician to justify my concerns.To clarify even further, if you have a notch that is ON THE END(the bearing portion) the notch can only be 1/4 of the depth of the joist.So in the case of a 2x10 floor joist, your notch could be just over 2" deep.
Do you have a code reference handy?
I have never had anyone with authority in this jurisdiction accept any notching. Engineers and all.
TJI's being illustrative of the point. Touch the top and bottom chord and it is yours to replace.
Cheers
TJIs have different structural characteristics than dimensional lumber.
In simple spans such as joists, the shear dominates the loading at the ends, and there is no moment at the ends. As you move out from the supports, the moment increases, and the shear become less of a concern.
When using dimensional lumber, the depth of memeber required to handle the moment at midspan, is usually greater than the actual depth of member required to carry the shear load at the ends. So, you can notch the member and still have sufficient strength to carry the load. In the mid span, becuase the moment is dominating, you drill holes at the center of the member. You need to size the hole so there is enough material left to resist the shear load, but you must leave the top and bottom intact to resist the moment.
If you look at flat bed semi trailers you will see that depth of the frame isn't very high at the tongue, or over the axles, where the load is shear, but is three or four times deeper at the middle of the trailer, where the moment is greatest.
This picture shows the shear (V), and moment (M) in a sumply loaded beam.
View Image
Thank you
That explanation and truck bed comparison is very instructive. Sort of an intuitive feel to it. Does this mean we could use elliptical joists? :)
I guess the general prohibition on notching stems from giving the plumber an inch and he takes most of the joist.
Probably still won't be setting them loose on the framing just the same.
I am a little smarter today.
Cheers
When using dimensional lumber, the depth of memeber required to handle the moment at midspan, is usually greater than the actual depth of member required to carry the shear load at the ends. So, you can notch the member and still have sufficient strength to carry the load. In the mid span, becuase the moment is dominating, you drill holes at the center of the member. You need to size the hole so there is enough material left to resist the shear load, but you must leave the top and bottom intact to resist the moment.
I think that's the clearest I have seen this topic explained, and I've tried to explain it myself many times.
Its Okay. Piffen posted a doc about notching in the boring holes thread.
Is every joist that has a notch been sistered?
And when you sistered... I assume you did a good job attaching sister joist to the old joist?
If so... I wonder if it would add any appreciable strength...
I'll let experts reply, but my guess would be "no".
Just want to be clear: When sistering a joist, isn't that basically like placing a newly supported joist next to the old one? Or is it simply attaching a new joist to the old one with nails / glue / whatever, without giving the new section end bearing?
I'm sure it could be both, and that somtimes you can't get to the bearing end and you're just trying to bridge a gap of weakness, but in all the joists i've sistered, I've made sure the new joist was bearing on the end -- in that case (and technically as long as the bridging was replaced), there would be no real reason to connect the 2 joists togehter...right?"It depends on the situation..."
"When sistering a joist, isn't that basically like placing a newly supported joist next to the old one?"
Only if it is supported at the same points as the original and is the same dimension. My understanding is that there can also be some issues of torque introduced in certain circumstances as when the load above is offset from the sistered element. Probably not too common though.
Joist patches are often just that -- patches to the damaged portion of the span, since it's often difficult to get a full joist reaching both supporting ends into an existing space. In those cases, you have to rely on the original joist for end support and the method of attachment becomes more important.
Mike HennessyPittsburgh, PA
I think you are correct with the definition for "sister". I think what I did is technically called "scabbing" since I just bridged the damaged area and did not go from support point to support point.
So how long is your scab/bridge?
They are anywhere from 3ft to 5ft long. The ones that I did are 3/4" ply glued and nailed on both sides and the previous plumber had done some with 2x material just nailed in place. Since there are pipes running through these I could not replace the 2x material so I just clamped them tight with my "Uncle Fester clamps" and added some more nails.
The floor structure seems pretty solid - I am 200+lbs and can walk on each joist assembly with any noticable deflection. I am adding 2 layers of plywood - glued and screwed so I assume that will help as well.
Seems like not quite enough in my experience with engineering types.
I would probably want a very serious opinion from an expert before I put anything over it. Just to sure and all. Hope and good wishes don't count for much when there is blame to apportion after the fact.
Cheers
You are correct in your analysis of the situation.
Yes filling the notch helps .
It would take more engineering knowledge than I have to say how much .
But It won't hurt that is for certain.
I have had to do it under engineers guidance to bring a notched joist up to an acceptable load bearing rating.
While you are right about the compressive force and also correct in that 2" out of 10" makes an 8 incher; I don't think that just filling the notch fixes it. A filler is still a break in the grain structure, similar to the way a big knot in a joist can weaken it.
You already sistered the joist so it should be good to go. The sister joist creates a sort of bridge for the forces to go through; sort of a new grain structure to re-direct the forces through. But then you must remember that the connection of the sister joist is then likely the weakest link.
If I run into a questionable situation like a big notch or rot and there is no good way to fully replace the joist, I use glue and nails or glue and through bolts if necessary.
I hope you are just over-thinking it, otherwise get an engineer.
DC
you are right. a tight fit into the notch will help resist the lateral compression there
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I don't know about strength for the joists, but one advantage of putting in dutchmen is that if you nail subfloor into that section, it won't tend to be pulled down and dip or anything like that.
CGI I have a correction.
While looking over the code book for our current project I came across the cutting, notching and drilling page dealing with joists. I was wrong when quoting from the code book.
I cant seem to find the scanned copy to post so I wil try to explain the best I can.
Floor joists-
If D= dimension of wood
No notches in middle 3rd
The notch can be on the top or bottom and only D/3 max width and D/6 max depth.
So a 2x10 floor joist can only have a 3"x1.5" notch in it.
Bearing ends-
The ends can be notched D/4 deep
Rafters or ceiling joists-
No notch in middle 3rd
Can be notched D/3 but can only be max D from support.
So a CJ can be notched 3" deep but only if the far end of the notch is 9 1/4" from the bearing point.
Holes can be drilled anywhere with a D/3 max and as long as you have 2" min from top and bottom of joist.
Hope this clarifies, sorry for the original misinformation.