BH or anyone – do what degree are cuts into the top of the top chord of a truss (as often happens when the roofer is cutting the openings for the through roof vent) practically acceptable?
See attachement
_______________________
10 …. I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have–Jesus Christ.
1 Corinthians 3:10-11
From building boxes and fitting face frames to installing doors and drawers, these techniques could be used for lots of cabinet projects.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial NowGet instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Saw the title of the thread - Went and took a couple of valium before reading it..................(-:
The technical answer is that every cut, notch, or hole drilled in a truss member has to be reviewed by an engineer. But in many cases that's overkill.
I'd temper it with a little common sense. If the cut you showed is on a 24' truss on a garage, I wouldn't worry about it. But if it's on a 40' scissor truss that's pretty well maxed out........That's a different story.
I would also be concerned about cuts in girder trusses of ANY size. (Trusses that have other trusses/beams hanging off of them) The lumber can easily be maxed out in these.
If the cut happens to be over a big knot or split it also might be a cause for concern.
If it's a new house, someone from the truss company will most likely come out and look at it for nothing. In an older one you just gotta find a really good looking truss guy like me to look at it.
The lottery:
Where millions of stupid people make one stupid person look smart.
Cuts in the lower tension chords would get my hackles up more than in the top compression chords. ...that's not a mistake, it's rustic
Bungalow - that's what I was thinking, but I suspect that the various force resolutions are a bit more complex in a truss than people like me understand!
BH - I wish I'd had my camera when I inspectred a garage wiith a gambrel rooff where all of the internal truss strusts had been cut out!_______________________
10 .... I have laid the foundation like an expert builder. Now others are building on it. But whoever is building on this foundation must be very careful.
11 For no one can lay any other foundation than the one we already have--Jesus Christ.
1 Corinthians 3:10-11
I wish I'd had my camera when I inspectred a garage wiith a gambrel rooff where all of the internal truss strusts had been cut out!
See! it was still standing wasn't it??!!
go ahead cut away!!!
WIMPS!!!Mr T
Do not try this at home!
I am an Experienced Professional!
Boss,
Since we're talking trusses here. I have a question for you. In my relatively recently built garage, the soffits overhang 3' in the area over the garage door. The only thing supporting the roof load there is 3 plus feet of 2X4 (see pics). is that sufficient?
Jon
Not to step on the Boss's toes, but it looks like those trusses were designed to be supported 3' in from the end to allow for the large overhangs. Notice there is a vertical member at the wall line. This is important, and I know Boss Hog has posted about this before. The truss information must be clear as to what is the actual clear span length and support locations. Also, I hope no one thinks they can nail a vertical onto a truss and call it a support point. The entire truss geometry is unique to the span length, overall length, rise and spacing.
I have run into "experienced" structural engineers that lacked the understanding of how simple a truss really is. ...that's not a mistake, it's rustic
I don't doubt it's O.K. - But it depends on the loading requirements in your area, lumber grade and species, etc.
Actually, I'm surprised they switched chord sizes near the end of the truss like they did. Most attic trusses I've seen keep the same top chord chord size all the way up. That's not necessarilly wrong - Just different.
The thing that struck me was the hole in the floor that just barely shows in "truss3.jpg". Is that a stairway? Are the trusses doubled around it, or did they cut some of the trusses for it?
Looks like you need to move some of the clutter from down below up to the attic.....................(-:Coward, n.: One who in a perilous emergency thinks with his legs. [Ambrose Bierce]
"Looks like you need to move some of the clutter from down below up to the attic."
Boss,
Just some stuff from the garden shed in there temporarily, as the shed is 200' in the corner of the property and tools have been used daily.
"The thing that struck me was the hole in the floor that just barely shows in "truss3.jpg". Is that a stairway? Are the trusses doubled around it, or did they cut some of the trusses for it?"
No stairway yet. I'm planning on putting in an electrically powered elevated platform. To answer your question, Yes a truss was cut. Look at the pic. The tension load is transferred to the adjacent doubled floor rafters (as well as the adjacent trusses through the 3/4 decking which was nailed, screwed and bonded with aircraft structural wood epoxy prior to cutting the hole.
Jon
What you did is exactly what I've been preaching against all these years here.
By cutting that truss, you've effectively adderd 50% more load to the adjacent trusses. They weren't designed for that.
Doesn't matter what type of glue you used.........Last week I stated this woman was the ugliest woman I had ever seen. I have since been visited by her sister and now wish to withdraw that statement. [Mark Twain]
"By cutting that truss, you've effectively adderd 50% more load to the adjacent trusses."
Boss,
Where did I add the load? Before and after measurements indicate absolutely no deflection in any direction. The cut floor joist was replaced by 2 2X10"s which rest on the top plates of the walls and were sistered to the adjacent trusses. They are now taking the extension and downward load of the cut one. The area around the hole has less up and down deflection than the rest of the floor. What am I missing?
Jon
Without seeing your situation first hand, I doubt anyone could tell you where you did or did not transfer load. The thing with trusses is that they are a manufactured product that is warrantied by their manufacturer. You can chop them up until Hell freezes over but without the okay of the engineer that designed them you will find your self up a creek without a boat or paddle if there is ever a problem. I have seen a couple of catastrophic failures of trusses both times it involved homeowners who cut them for whole house fans and the stairway to heaven in the attic. One of the homeowners told me that he had cut the bottom cords of two trusses over a year before the failure and thought his repair had been adequate. He did end up suing the truss company, but the lawyer representing the truss company gave him a real education in liability. It seems simple enough to me as a framing contractor always looking to avoid liability issues that when ever we have a question regarding modifying a truss we get with the guy that made them and ask him.
"The thing with trusses is...... You can chop them up until Hell freezes over but without the okay of the engineer that designed them you will find your self up a creek without a boat or paddle if there is ever a problem".
That's why I posted my initial question. When the trusses where delivered, they came with an envelope that had print-outs (drawings) of the trusses. In one corner it stated that they were computer generated, and they should be reviewed by an engineer prior to installation. When I questioned the builder about the three plus foot cantilevering, he told me not to worry, the software calculates everything just right.
Jon
Ah, nothing like a computer program in one hand and a Sawzall in the other.
Your roof is designed for a maximum occurence of wind, snow, live, or a combination. the codes have become more prescriptive over the years, but there is a hurricance Andrew or Loma-Prieta earthquake preceding each major code change. Your house may never experience the maximum design load, which is good because I hear 500-year storms suck to have a BBQ in. ...that's not a mistake, it's rustic
"Ah, nothing like a computer program in one hand and a Sawzall in the other."
Jeff,
Funny you say those two things in one sentence. We have just about the best CAD/CAM/CAE software on the planet at work and also do prototyping for MKE Tool, makers of the SawzAll. There is a new one coming out soon. Many a remodeler or plumber will appreciate it. Can't say any more.
Jon
Hey Jon,
Here in my little slice of California, our trusses come with those sheets also, but the over all design is wet signed by a engineer. The great majority of my work is for builders, and not homeowners. Regardless, I am not afraid to pick up the phone and ask questions, and I have learned a lot from various truss engineers and manufacturers. A three foot cantilever would have received my full attention. I would have called the truss manufacturer for some clarification and reassurance despite what the builder said. That is because it doesn't matter what the builder says, he did not design the trusses.
I am not condemning anything that you have done, I am only passing on a little bit of what I have learned in 26 years of framing buildings. Please get your modifications checked out for a little peace of mind and to ease Boss Hog's ulcer. As a footnote, Boss Hog's advice and tips usually parallel what I run into out in the field. In my opinion he knows where of he speaks. I will now leave the soapbox. Good luck.
Each truss is designed to carry 2' of load. (Assuming they're 2' O.C.)
Cut the bottom chord out of one truss, and the adjacent trusses have to take half the load of that one.
The fact that they have no noticeable deflection yet isn't significant. That can easily change over time, as the trusses take on and lose live loads.
I did a thread a wile back called Cutting trusses for skylights which covers a lot of this in more detail.I have this nagging fear that everyone is out to make me paranoid
I have this nagging fear that everyone is out to make me paranoid
Kinda appropriate to another cut truss story, don't ya think?
Never be afraid to try something new. Remember, amateurs built the ark, Professionals built the Titanic.
"Each truss is designed to carry 2' of load. (Assuming they're 2' O.C.)
Cut the bottom chord out of one truss, and the adjacent trusses have to take half the load of that one."
Boss,
I understand that. By sistering equal length 2X10's, plus bonding the the floor, as well as adding doubled 2X10's across the opening, didn't I take care of that issue? (I did read your thread, the bonding IMO took care of the extention issue)
One interesting comment. When I cut the truss, (after all the reinforcing) the gap from the saw cut, nor the height of anything moved. Not even .002".
I have the ability to do finite element analysis at work. If I have the time, I think I may model up the before and after and see what changed.
Jon
Jon
Edited 6/26/2003 11:03:10 PM ET by WorkshopJon
John -
First off, I wanted to say I'm not trying to bust your chops here or make you look bad - I just don't agree with your conclusions.
Sistering equal lengths of 2X10 to the bottom chord probably didn't do much of anything. The bottom chord isn't what supports the rest of the truss - It's a complex system of forces in the chords and webs.
I don't meant that you should rush out and hire an engineer and spend a bunch of money analyzing the problem. (Although that's the technically correct response)
I just feel that cutting the bottom chord of attic trusses (or ANY trusses) is a bad idea in general, and shouldn't be done.
BTW - The pictures you showed are a 3' overhang, not cantilever. It's an overhang if the top chord is the only thing that sticks out past the plate. It's a cantilever if the bottom chord extends out past the plate and meets the top chord away from the wall.
Again, not trying to bust yer chops - Just wanna get the right info out there. I can do pictures if the difference between the 2 isn't clear.Q: Why do brides wear white?A: Because it's nice if the dishwasher matches the stove and refrigerator.
Boss,
"I'm not trying to bust your chops here"
I didn't think you were, that's just how forums work.
Kinda' hard for me to debate trusses with the forum expert, however, but I'm still going to try somewhat.
"Sistering equal lengths of 2X10 to the bottom chord probably didn't do much of anything."
Actually, didn't it at minimum add to the extension strength of the bottom cord?
"I just feel that cutting the bottom chord of attic trusses (or ANY trusses) is a bad idea in general..."
I agree with you on that, just sometimes you have no choice. Best one can do is minimize and/or spread the loads.
Is what I did as good as not having done it at all?
Of course not, but I needed a way to get up to the attic. Based on my education in physics, I still feel that the way I triangulated everything is sufficient for the loads that that floor and roof will see. It has already been sujected to 60 plus mph winds. This all was done over a year ago, and there is no evidence at all of any thing moving, pulling apart or bending. (see additional pics)
FYI, I would never do that to a 2X4 truss, nor cut a truss for a skylite. I still maintain that by bonding the entire floor with an adhesive designed for wood aircraft wing spars (which are a form of truss), as well as doubling up on the 2X10's, and adding doubled 2X10's to connect the cut truss to the sistered truss rafters, I sufficiently spread and redirected the loads around the hole.
The only thing I can think of that I can do in addition is make large angle irons (U's) with a web to go in all the corners, but there is no empirical evidence to suggest that is needed.
Should I notice any changes, Then I'll worry. Like I said before, I have all the before measurements, so that won't be a problem.
Jon
Edited 6/28/2003 6:42:25 AM ET by WorkshopJon
Boss,
I finally got around to CAD modeling my trusses and the changes I made. Then running a finite element analysis on everything. One word... EEEECK. I'm going to quote myself
"I still feel that the way I triangulated everything is sufficient for the loads that that floor and roof will see.....there is no evidence at all of any thing moving, pulling apart or bending."
And retract that statement.
You weren't kidding when you said "It's a complex system of forces in the chords and webs."
What has now become obvious is that I shifted a point load from under the knee wall to the area adjacent to the hole as well as a bunch of other stuff. Also, the floor joists are not just in extension, but compression also, and it is non-linear. And a bunch of more minor loads have moved.
Interestingly, under light loads, the FEA predicts the the floor will be more ridged (after my modifications, which it is), but under heavier loads (when the trusses start to work) the area around the hole flexes more.
Did come up with a fix though. (one of the neat things about the software ( http://www.eds.com/products/plm/unigraphics_nx/ if you're curious) is I can easily model in and remove stuff, basically doing "what if" analysis. The fix that I came up with is that I need to sheath the knee walls and sheath the area underneath the cut truss (spanning it from wall to wall and across to the adjacent trusses) effectively boxing the floor and directing the forces from the cut truss into the reinforced ones. It still won't be as strong under certain conditions, but will definitely be better.
Thanks for your words of caution,
Jon
As long as ya already hacked it up, why not go ahead and put double joist hangers in each corner of the hole and a single hanger on each of those cut bottom chords that butt up to the double. Use min 10p nails too except for the attachment to the cut chord which will be joist hanger nails.
Matt
workshop...
takes a big cyber man to admit he was wrong.. good move...
as boss has been 'splaining , lo these many years..
everything in a truss system is interdependent.. if i have trusses 2' OC.. and want to add a 3' hole.. i tell my truss designer to figure it in the original plan.. invariably, they will double the trusses on each side of the hole.. but whatever they do.. i will have a stamped design and layout .. one copy to the building inspector and one copy in the customers's permanent file...
my heirs can trash the files... but you never know when the next homeowner will take issue with our work...Mike Smith Rhode Island : Design / Build / Repair / Restore
you are a big man Jon.
Using finite element analysis on a roof truss is ridiculous overkill. Simple residential roof trusses can be solved by hand.
...that's not a mistake, it's rustic
Edited 7/1/2003 12:04:24 AM ET by Bungalow Jeff
"Simple residential roof trusses can be solved by hand."
Not really. The old pin joint ananysis they teach in engineering school is being phased out. I suspect within 5 years or so it won't be allowed anymore.
Edit: Forgot to add that these were attic trusses too, so calcing them by hand would be qite difficult, and the pin joint model doesn't apply.
If you choose not to decide, you still have made a choice.
Edited 7/1/2003 6:59:10 AM ET by Boss Hog
"Using finite element analysis on a roof truss is ridiculous overkill. Simple residential roof trusses can be solved by hand."
Jeff,
Maybe, (though not according to The Boss) but I have virtually unlimited access to a lot of tools the average Joe does not. Besides, it was a learning experience and didn't cost me anything other than my time.
Jon
You know, I thought about Boss' comment, and he is absolutely right. Pre-fab trusses are like any other assembly catalog item and it's only natural to cut the cost of thousands of trusses by using finite element to get the most out of a 2x4 chord truss before moving up in size.
...that's not a mistake, it's rustic
I don't really know much about the program you're using, so it's hard to second guess the results you're coming up with. Sheathing the kneewalls sounds interesting. But I'm not exactly sure what it would or wouldn't do.
I do agree with DIRISHINME about the hangers, though.
You know, I admitted that I was wrong on this forum once, (and ONLY once) and no one said a word. You did it, and a bunch of people pat you on the back. Maybe they just weren't surprised that I was wrong ???...............(-:Many things are worth dying for, but none worth killing for.
Boss,
One thing I never mentioned in this thread is what lead to me doing what I did (cutting the truss) in the first place.
Where I live, you really don't need much in the way of any kind of plans to build an outbuilding. Adding the attic trusses were a last minute verbal over the phone with my GC. I was not around when the building was framed and sheathed and just assumed he would frame out a passage to get up to the attic.
When I caught up with him after the roof was on, he ASKED ME how I planned on getting up there...I thought that he would have planned for that...Given all the delays (months) just to get him going, I just shrugged it off. Obviously there was some poor communication at both ends.
While I had always heard it was a bad idea to cut a truss, in our litigious society, we are warned about stuff all the time. How many people heed the warnings on the back of of a piece of sandpaper to wear proper protective gear before using it?
I thought my framing was sufficient, but obviusly it wasn't. So I learned a few things. That's what you all are here for. BTW, this all happened before my Breaktime days.
Jon
Well, I don't take it TOO seriously when people cut trusses - Don't need to get an ulcer. And if you did it pre-Breaktime that counts for a lot.......(-:
I'm not surprised that your GC didn't think about how to get up into the attic. I've warned guys repeatedly to think about it ahead of time, and they'll still say: "We'll figure it out later".
I understand the fact that we're warned about stuff all the time. It's hard to know sometimes which warnings are legitimate and which ones are just to cover someone's butt.
To the regulars here I probably sound like a broken record, talking about trusses and floor vibration all the time. (And bringing up the "spec house from hell" thread) But I always try to get out the facts as I see them - Might keep someone from making a mistake that just happens to read the thread.
And again, please understand I wasn't trying to pick on you or make you look bad. I was trying to stick to my guns and yet be civil about it. Hoppefully I've done that. Not only am I redundant and superfluous, but I also tend to use more words than necessary
you haven't really mentioned that house from hell in a while, I trust you are still stuck with it?
Never be afraid to try something new. Remember, amateurs built the ark, Professionals built the Titanic.
Yes, we're definitely stuck with the "spec house from hell". We're on our 3rd realtor trying to sell it, and as of yet haven't even had a single offer on the house through them. Not even a lowball one.
We've talked about moving into it (again), but haven't reached an agreement on it. DW isn't really for it, and the payments/taxes will be hard to swing. But I don't think it's going to sell. The local economy is getting worse - The school system laid off 35 teachers & other staff.
So if it's gonna be a boat anchor around our necks, I figure we ought to be able to enjoy the dumb thing while we're losing our #### on it. Life is playing a violin solo in public and learning the instrument as one goes on.
I don't agree with anything you did to the trusses. In my area the inspectors would have failed this in a heart beet. And the engineering fees and repair cost alone would be more than what it would have been have girder trusses added to cary the extra load. But if you think this is fine go with it, but I stongly sugest you put some hangers on your intersections.
I don't think I'd worry about that one.
This one on the other hand.
Homeowner cut the webs out of a 3 ply girder. and the top chords out of three attic trusses. The cables are the goofy repair his bridge engineer buddy came up with (they weren't even tight).
The second pic the next post shows the beam we installed along with a few other items my engineer came up with.
Tom
Edited 6/26/2003 2:04:19 PM ET by Tommy B.
beam.Tom
What's wrong with that repair ???
Looks fine to me..................(-:We're kind of like the Simpsons on crack. [Axel Rose]
Tommy, of course the cables weren't tight....that proves that he didn't do anything wrong by cutting the trusses, obviously they were over-built to begin with.
BTW, you......really.......need.......to......download.........Irfanview........and........learn........how........to....
.........use.........it........on.........your.........pictures........!Do it right, or do it twice.
What's irfanview?
I'll download it when you stop writing three feet wide:)
I got a cable connection so they download quick enough for me. I can't relate to you poor dial up folk.Tom
Try a search here for irfanview, if that doesn't work, do a web search. It's a neat program that converts any file format to something else, but more importantly it will reduce the size of the jpg pics down to under 100k with essentially no loss of quality, especially for viewing on your pc. makes them load way faster.Do it right, or do it twice.
As a sales rep for one of the largest truss companies in the us I can tell you we do not like to see any cuts made to any part of a truss unless it is a gable truss. But their is not stadard on how much can be cut, due to different stress points on the truss. I can say I have had up to 3/4 of a inch cut at a tapper up a top cord due to a truss not plaining with another truss. The best answer is to try to find the truss company who mfg your trusses and have the sales rep check it out. If you are unable to find this information, I would sister a 2x6 spf to both sides of the truss from the peek to the heel of the truss to be safe. If you can't do both sides I would do a 2x6 yp #2 or better.
Which truss company do you work for?
I used to work for Shelter Systems in a previous life...Happiness, n.: An agreeable sensation arising from contemplating the misery of another.
I work for Stark Truss Co Inc
Hate to tell you, but I've never heard of your company. Where is the company located?
I work for Rehkemper, in south central Illinois.
Glad to have another truss guy hanging around. They always pick on me here when I tell 'em not to build their own trusses.................(-:In our civilization, and under our republican form of government, intelligence is so highly honored that it is rewarded by exemption from the cares of office.
Well we have 5 in ohio 1in indiana 2 in Kansas 1 in Kentucky 1 in Missouri 2 in Florida 2 in South Carolina and 2 in Texas and more comming. I have heard of you you are one of my compettors.
A competitor, huh ??? Guess I'm gonna have to watch what I say around here now....................(-:
You must work in the Missouri plant, then and sell in the St. Louis market?
I work in their sattelite plant at Litchfield, Illinois. We ship about 5 houses a day to the tract builders in the St. Louis market. Don't know how many the main plant ships.
I'm a truss designer, not a salesman. I mainly do roof truss layout and design for custom homes in an area from Springfield, Illinois down towards Alton.
Like I said, I'm glad to have another truss guy on the board. Hope you'll hang around and post often.In the land of the blind, the one-eyed man is king.
Cool.. Truss wars.
Now pass the plywood scabs and drywall screws... Got some trusses to build.
don't forget the wood glue.
Thanks for the reminder... School Time Elmers' white it is....
I hope that's a joke about drywall screws. They should never be used for building trusses or for repairs. The have no structural strength at all.
It was sort of an inside joke. I have a strong disdain for their use in any application other than hanging drywall. I've chided people so often about it that my reputaion precedes me with some of these jokesters making statements like, "Watch out for Piffin when you say that"
Glad to seed another pro here! Especially one who knows how to be young!
We like to spice our boring tech talk with a little humour here..
Excellence is its own reward!
Hey b... you truss guys are all ways on top of things but "they have no structural strength at all " that you used in reference to Piffin screws ....I mean dry wall screws means what? I've always wondered what the shear strength is or some rating for holding power , seriously you got any info.
Drywall screws are stronger than drywall -- but not by much. Making them any stronger than they have to be would be a waste of money, and multiply that by the number of drywall screws in the world -- it would add up to a lot.
-- J.S.
Didn't find much out there on shear strength, here is one mfgs ratings, for what they're worth:
http://www.intercorpusa.com/test.htm
Well thanks for having me
Most of my work is in the St. Carles and St. louis counties. I do work for alot of the track builders in the area. I also do some work in the Ill area also.