Trusses wrong pitch… gonna change ’em
We set a roof truss package this morning, and when the owner came home he pointed out that they were the wrong pitch–his error, and his architect’s.
They span about 16′, all 2x4s, have a king post in the middle, and are 7/12 pitch. The correct pitch is 8/12. According to my CM calculator, we could rip wedges out of 2×8, amend those to the top chords, and have just about the right thing.
The architect is adamant that this is a fine thing to do, and I probably believe him. He also says the BI will pass this and I believe that too.
The two methods that have been discussed are to either use Simpson ‘ripper’ clips (RC1.56) to piggyback the big wedges on top of the trusses, or use splice plates (maybe TP57s) to do so. I suppose another option would simply be to sister onto the sides of the top chords.
Naturally, I ain’t happy about this. We closed down early today, lacking a way to proceed. The trusses are perfectly set and I’m not taking them down, and I’m not sticking the owner with his mistake on my project.
Anyone done this, and how?
Replies
I'm not sticking the owner with his mistake on my project.
I hope you're going to charge him for the time & material to make the change.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
No question about that. There have been some other design shortcomings on this one that have led to changes midstream. Makes it a little uncomfortable, but I have to eat every day, not just on the days when the designer does a good job.
I'd be inclined to go with the RC's but I'd also have the calc's done on the required nailing pattern for ordinary sheathing and then add sufficient number of straps between the rips and the trusses to transfer the uplift loads to the trusses where they would have been in the first place. RC's would be more for alignment than secure attachment.
You'll also need to rethink blocking between the trusses and the new heights caused by the piggybacks as well as the outlookers if you have them.
Our BI would require new stamped drawings and calcs on file.
The architect endorsed either of the ideas I mentioned and said that he would file a letter with the BI so stating. He's not an engineer but he is licensed and is an old-timer here, so I think that will fly.
I'm considering having the owner sign a C/O agreeing that we are to proceed based on the architect's statements and that I am not liable if the BI later asks for more work, or more documentation.
Considering that it only takes a couple hours to set trusses, if that, I'd take them down and start over. I think I'd be way ahead time wise and not have to worry about the lateral forces put on a scabbed piece. You'll have to re-cut all the tails, too. Of course, you are only talking a total difference in height of 8". Anyone with some common sense would leave it alone, otherwise I'd tell them to call when the new trusses showed up.
Beat it to fit / Paint it to match
I've never used a truss company that had quicker than a 2 week turn-around time. Since this is a addition, I don't know if he has part of the old structure "opened up" but if so, I would guess that it would "heavily weight" decision too.
David,
By the time you do all this extra work, can't you just stick frame it with rafters along side of the trusses or just get rid of the trusses? It's only a 16' span. Does this have to be a 8/12 pitch because your matching the existing house planing into an existing roof and matching fascia lines and overhangs? The change for a stick frame can be signed off from the same Architect who designed it and screwed up on them.
Joe, I thought about just going with sticks but honestly I can get back on track quicker just modifying the trusses. In the morning we'll rip some 2x8s into those shims and get them on there. 13 - 2x8 x 12' ripped diagonally and some time attaching them... we'll be starting to sheathe in a couple of hours. Also, a lot less lumber than if I trash the trusses and start will all new. Got to get out of there and on to about 11 other jobs!
I would sister them with 2x6's or 2x8's. The time spent ripping if far greater than the time spent nailing.
In any event, I would let the truss company dictate the repair, not the architect.
Also, since the homeower would pay for the materials and repair time, I'd run the options by him and let him decide, if there was any substantial time difference.
blue
I'm with blue, sister them this happened to us last summer, we sistered both sides. I wouldn't want my roof sitting on shims. Or tear it all off and rafter it sell the trusses to someone for a garage 16' may be an easy sell to someone.You're entitled to sh!t.---Tony Soprano
I'm with the others who say get the buy-in from the truss company. Weather you sister or add wedges you are adding weight to the structure (be it minimal) and you are going to be using the trusses in a manner in which they were not designed for.
David,By the time you rip 13- 2x8's on an angle and nail them in and then using some kind of simpson strap you can do like I said in my first post and nail along side of them just making a plumbcut on each end and you'll be done ten times faster then what your saying and be ready to sheath in one hour instead of a couple hours. Yes, you'll use a little more material but who gives a crap, the homeowner will have to pay for that and your time is cut in half.Joe Carola
I'm with Blue - Adding something to the side seems a lot easier than ripping and adding to the top. It allows more flexability if on of the rips or one or the top chords aren't perfectly straight. If you need something for the BI, the truss company may be able to provide it. Couldn't hurt to ask.
Q: If seagull fly over the sea, what flies over the bay? A: Bagels
I'm persuaded that sistering would be faster by a bit, but I'm not obliged to be extra-fast on this. What concerns me is that near the ridge I would have almost no connection between the truss and the sistered 2x8 (if I use 2x8 for this) because the added rise I need is about 7-1/2". So, a 2x8 goes from fully sistered to the truss at the heel, to not at all at the ridge. Since shear has to be transferred from the 2x8 to the truss, I'm not sure how that would be made to fly. It seems more likely that a shim on top of the truss could be backed up by engineering, even if they make us nail on a shidload of tie plate. If the truss company or the BI somehow does not like the sistering, then we gotta 'nother problem.
I suppose I should say that I'm predisposed to the shims because it was an engineered detail for a flat roof I once did. We framed the ceiling with TJIs and then added the roof slope on top with ripper clips and 2x shims.
You guys are probably right, I'm probably less right. Perhaps what I'm going to do this morning is ask the lumberyard to get me a few words of wisdom from the truss company. It would not surprise me if they have a semi-canned answer for this one, already xeroxed and ready to fax out.
Every time I run into something like this, my tendency is to work like hell and "fix" it so I can get back "on track" as you said. What I end up doing then is rushing into a solution that I might not have used if I had given myself time to think a bit, to consider various solutions. Not good.
I recommend waitng until you are SURE you see the best "fix", David. Better to lose a few days now than build something questionable with your name on it, regardless of who signed off on it. You are trying to build YOUR name, right? YOUR reputation. Tipi, Tipi, Tipi!
http://www.asmallwoodworkingcompany.com
"...I'm not obliged to be extra-fast on this."
So you're just half-fast ???
Sorry (-:
"Since shear has to be transferred from the 2x8 to the truss, I'm not sure how that would be made to fly."
Technically, you're correct - The top chord is in compression and must be continually sheathed. But since these trusses are so small I doubt it will be that big of a deal.
"...I'm predisposed to the shims because it was an engineered detail for a flat roof I once did. We framed the ceiling with TJIs and then added the roof slope on top with ripper clips and 2x shims."
In that case, the I-joists should have been sheathed to restrain their top flanges. If that wasn't done, I'd say the detail is wrong and probably wouldn't pass with the manufacturer of the I-joists.
"What I'm going to do this morning is ask the lumberyard to get me a few words of wisdom from the truss company. It would not surprise me if they have a semi-canned answer for this one, already xeroxed and ready to fax out."
I've never seen a "canned" solution to this. But I'm sure they'll come up with something. It may take a couple of days, depending on how busy their engineers are.
If you use something like 2X6 nailers, the top chord sheathing could easily be replaced with some purlins that they can specify. And it might only take a couple of them.
Would ya let us know what endds up happening? It might help someone else on this board, and I may learn a new trick.
What makes you think you can just walk in there and take whatever you want?
They're called boobs, Ed. [Albert Finneyand Julia Roberts in "Erin Brockovich"]
I've definitely decided not to 'fix' anything until someone in authority OKs it.
I made a sketch showing the rip method and the sister method and I'm going to drop it off at the lumberyard in a few minutes. We have other framing to do that will take half a day. If the truss company gives a verbal indication of how to proceed, we'll go ahead. I'd say it's 75% that I can get something from them this morning, to be followed up in writing.
If they can't do that, my structural engineer can, and I'll call him at lunch. He usually does small stuff over the phone and then sends me the paperwork.
When I said I don't have to be super-fast, I mean that I don't care if the client pays me for a quick, easy, very affordable solution, or a semi-quick, easy, less-affordable solution. We're talking a few hours either way. This situation ain't on me. I am providing framing labor only, no materials, no consulting, just show up and start cutting the lumber that the owner ordered. This is very different from my usual. Normally the whole thing would be my responsibility and I would have spent several hours on site and at my desk troubleshooting the job before day 1.
The silly thing is, the note on the plans is "New roof to match existing house, 7:12 pitch". Normally I find it annoying when the designer says "Verify in Field" but in this case I wish he had, because I would have checked that for the owner before he ordered these damn things.
DAVID,
EXCELENT CHOICE TO SLOW DOWN AND FIND THE RIGHT SOLUTION... NOT EASY TO DO.
IN MY HUMBLE OPINION, I LIKE THE WEDGES FOR THE SIMPLE FACT THE WEIGHT IS BEING TRANSFERED DIRECTLY TO THE TRUSS AND HAVING TO GO THROUGH THE NAILS. WOULD YOU CONSIDER ONLY NAILING HEADERS TO THE KING AND SKIP THE JACK?? I KNOW THIS ISN'T A PERFECT COMPARISON BUT HELPS ILLUSTRATE MY THOUGHT PROCESS. OVER TIME FASTENERS CORRODE, THEN WHAT.
GOOD LUCK!!
The main advantage of the wedge is that there's basically no way it can fail "downward", so long as it's adequately strapped for uplift (*). The other approaches CAN fail, though one can argue about how likely failure would be, and what form it would take. And they have similar uplift dangers to the wedge. Even as an engineer I favor schemes that can't fail over ones that an engineer assures you won't fail.
(*) Actually, there is another failure mode besides uplift. That would be the trusses racking. But the same thing could occur with a scab, though not as easily. For any of the solutions it's probably wise to install diagonal bridging of the trusses, even if not required by code or engineering specs.
If ignorance is bliss why aren't more people
happy?
Being as you're an injunear - I'm curious what you think about how engineers sometimes come up with wildly different theories and solutions to stuff...
Q: What do you get when you cross Viagra with Rogaine?
A: Don King.
If you're an engineer you don't think, you just plug-n-chug.
If ignorance is bliss why aren't more people
happy?
"The main advantage of the wedge is that there's basically no way it can fail "downward", so long as it's adequately strapped for uplift (*). The other approaches CAN fail, though one can argue about how likely failure would be, and what form it would take."I suggested nailing rafters along side the trusses and nailing them into the trusses. With that said there would be a plumbcut at the top and a birdsmouth at the bottom sitting on the top plate. He said that the top of the new rafters would stick up 7-1/2" above the trusses and I said to put a ridge in there.So what that really is, is just stick framing new rafters along side the new trusses with a ridge. So why would those rafters fail? You keep the trusses in there for the ceiling and sheath the new rafters. You can brace the trusses up and not even nail the new rafters to the trusses and there's no wait on the trusses at all.Joe Carola
Yeah, that would work, so long as you were careful to install the new members precisely as if they were stick-framed. But even a stick-frame roof can fail, if not properly constrained against thrust at the plate. The main danger here would be a tendency to believe that standard stick-framing practices did not need to be followed.
If ignorance is bliss why aren't more people
happy?
Boss has said it many time...ITS ONLY A 16' SPAN!
We are talking about 2x 12 rafters, with full bearing on the plate and fully bearing on the top and IT'S ONLY A 16' SPAN!
If you look in the dictionary for the definition of overbuild and overkill, you would see that "solution". Frankly, I'm amazed that the engineer managed to warn about sideways torque with a straight face. I know I would have busted a laugh at him, till if figured out he was serious. Once I knew he was serious, I'd mark his name in my little black book of people I'd never seek information from again!
It's only a 16' span!!!!! The freaking rafter is 9' 7". You could park an elephant up there and if the 2x12 failed, the underlying trusses would snag him!
I would take the truss companie suggestion and run it by the homeowner and get the go ahead for the repair. I'd never even mention that wacko engineer's "fears".
blue
ps It's only a 16' span!
"Yeah, that would work, so long as you were careful to install the new members precisely as if they were stick-framed. But even a stick-frame roof can fail, if not properly constrained against thrust at the plate. The main danger here would be a tendency to believe that standard stick-framing practices did not need to be followed."Dan,That's just all common sense.His trusses are in already. His Engineer or whoever is coming up with the solutions are looking way to far into this and making it a big deal for nothing.The span is only 16' which has been mentioned and slipping rafters in along side the trusses and stick framing would work and no one would have to worry what side pressure on the trusses or top pressure if you ripped 2x's and nailed them on top with all these simpson ties. These little rafters could be done in no time and not have anything to do with the trusses.Joe Carola
Just FYI - Using all caps is like shouting, and is considered to be rude.
Finding an honest politician is a difficult thing to do. Not nearly as difficult, however, as finding a black man with a toupee.
On that I-joist + shim roof there was a lot of blocking between the I's, and a lot of ripper clips. Fully engineered and inspected job about 500 yards from the Hayward fault.
A semi-humorous and semi-related story comes to mind. A builder I know who's a class-A jerk orders trusses for a house. (No real blueprint - Just a half-a$$ed sketch) Trusses end up being taller than he wants. So he figures he's gonna change the pitch of them. He cuts all the webs out of them with a chainsaw, then stand the bunk of trusses upright. (He has a forklift) He picks up a bunk of plywood and sets it on the peak of the trusses to push them down and make the pitch lower. He ended up with a pile of scrap lumber, which he pushed together and burned. GC proclaims he ain't gonna pay for the trusses, since they were defective. The truss comany and the lumberyard he bought them from refuse to back down. GC ends up paying for another set of trusses so he could finish the house..Nothing remotely to do with your situation - I just thought of it this morning...Sometimes jerks reap what they sow. (-:
Pretzel makers are a twisted bunch.
I dropped my sketch off at the lumberyard this AM. I deal directly with the owner, and he called the truss company while I was standing there. They are working on it and hopefully we'll hear shortly. Astonishing as it is, this was a new one to the lumberyard owner... he'd never had this problem before. I can only assume this means other people just use what they get, right or wrong, or do field mods.
FWIW, the addition has its gable next to the larger, taller gable on the house. The difference between 7:12 and 8:12 is really visually annoying. It would have been better if the ones we got were 5:12 or something, a big difference instead of a small one. The small one looks like the mistake that it is. Oh yeah, the property has a studio behind the addition that's also 8:12.
I haven't done much framing but that's one thing that I learned right off when we did our covered deck. We figured it was a 4:12 pitch, but it was really 4.25:12, and we only discovered this after cutting about half the rafters for the deck. Already had the ridge beam up too.Would have looked like carp if we left it, since were were tucking the deck roof right under the house gable end. So we added a 2x to the ridge beam and cut new rafters.I learned on that project to always measure. Never assume that things are standard dimensions, level, plumb, or othewise consistent.
If ignorance is bliss why aren't more people
happy?
Boss, that might be the greatest truss story ever told!
Thanks for the laugh! I can just picture thiat a hole out there...Some guys are so stupid...
blue
"What concerns me is that near the ridge I would have almost no connection between the truss and the sistered 2x8 (if I use 2x8 for this) because the added rise I need is about 7-1/2"."Why can't you just stick a 2x8 ridge in there then? Cut the ratfters back 3/4" at the top plumbcut on each side and slide a full length ridge in there.Joe Carola
What concerns me is that near the ridge I would have almost no connection between the truss and the sistered 2x8 (if I use 2x8 for this) because the added rise I need is about 7-1/2".
You've probably solved it by now, but was wondering . . . couldn't a 2 x 4 follow the original 7:12 angle on the 2 x 8 (until it reached the top plane) and then the 2 x 8 would cross over the truss and scab to it? The 2 x 4 might need some ripping at some point, but the crossover doesn't need to be pretty.
Ripping a 2 x 8 along its length leaves little material at one end for connections and an opportunity for splitting/breaking.
Ah, well. One of those things.
Why can't you use a 2x8 ridge at the top for the sistered joists?
That's a brilliant suggestion Arrowpov. That's what I'd do if I was worried about the top section of the sistered members.
I myself wouldn't worry one iota on a 16' span.
Also, if the engineer did spec a ridge beam, I'd probably put in a dropped 2x6 to allow for a ridge vent.
blue
OK... two engineered solutions emerged today.
Truss company's solution is to sister 2x12 onto one side of each top chord. Level cut at the top plate, plumb cut at the ridge, no ridge board shown. Nail 10d at 6" O.C.
Local SE's solution is to rip the 2x8s and attach them to the top of the trusses with Simpson RC clips at 24" O.C. except at the very bottom. 1x8 ridge board also. He frowned on the idea of sistering 2x12s, not liking the idea of the side load that creates (that's not engineer speak I just wrote there, it's a layman's summation of what I think I heard him saying).
David,My late and unprofessional opinion would be to rip and lay on top, like you wanted to do.Sistering would appear to me (whether right or wrong) sloppy.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Whichever solution you go with..... make the owner happy (he's paying).... cover your exprenses..... and get that written engineering "stamp" of approval for the structural change.
I don't see the problem with the 2x12 sistered to the side. It will be bearing on the top plate, and against the ridge board. The nails into the truss will keep it from flopping over, and you could run blocking if needed. Heck, if a 2x12 won't carry the roof load for a 16' span ...
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
What ridge board?
If ignorance is bliss why aren't more people
happy?
the one FE is gonna stop in and install....Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!<!----><!---->
Forget the primal scream, just ROAR!!!
What ridge board?
Oops.
Hey ... at least I didn't say ridge beam.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Edited 3/23/2006 8:56 am ET by FastEddie
Don't need a ridge board with the trusses there. Just butt the rafter ends at the ridge.SamT
Maybe you should just take down the trusses and stick frame the roof. Sounds like that's almost what they want you to do.Beat it to fit / Paint it to match
Not gonna happen, give it a rest.
David, if you're going with the method of building up the top of the trusses, maybe consider getting the truss co. to sign off on that.
I'm just imagining a situation where for some totally unrelated reason the roof goes down, Owner/Ins. co. starts looking for folks to tag, and as quick as you can say "unapproved field mod to trusses," the truss co is looking to point all fingers at you and cut and run. You could then point to the engineer, but by that point it's getting messy.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
The engineer's sign-off is what it's going to be based on. As far as I'm concerned, that's enough. If this were anything complicated or remotely risky I would just have the trusses replaced entirely, not modify them. There's absolutely no safety issue in my mind, just the issues of cost/speed/lumber waste.
When you started this thread, did you think it would get this much attention ??? Hard to say what's gonna create a ruckus around here...I don't buy the idea that nailing something alongside a truss will create a side load. But it's a line I've heard before.If you ned to lean on them, it may help to remind them that this is ONLY a 16' truss. It would be pretty hard to screw up something that small. Thanks for keeping us updated.
One of the greatest labour-saving inventions of today is tomorrow. [Vincent T. Foss]
I don't know if I think it's a big deal either, but the local engineer, who I think is very sharp, scowled at the idea. And sistering does put all the load off to one side of the truss.
Who cares! I have a stamped letter telling me what to do and as far as I'm concerned I can hang my hat on it. For good measure the architect is running it past the BI this morning.
I don't buy the side loading thing at all - Mainly because of the roof sheathing. The plywood forms a diaphram, which will hold the scab in a plumb position. Half the wieght from the scab would bear on the seat cut at the wall anyway. The scab would end up working more like a rafter than anything. And like I've said a couple of time already - It's only a 16' truss for God's sake. I think he's being overly picky.
If a pig loses its voice, is it disgruntled?
I think the truss engineer distinguished himself by coming up with such an overkill solution. Dealing with engineers is amusing anyway. They often have such different ideas about what to do. Maybe I'm guilty of calling the guy that I know will give me a solution I like.
It is funny sometimes how they come up with such wildly different ideas sometimes. But it can also be terribly annoying. (As you're finding out)It always seems worse when trusses are involved. I can see them getting worked up over a 60' scissor truss, or something else really big. But this is too small a truss to get worked up over. The forces are miniscule.I don't blame you for calling the guy you wanted to. We all have our favorite subs and such. No harm in that.I doubt the engineer from the truss place was really trying to overkill the thing. He was just using the lumber size that would allow for nailing along the entire top chord. Personally, I like that solution better than the one that you like. But I obviously am not the one doing the repair.
Men don't care what's on TV. They only care what ELSE is on TV. [Jerry Seinfeld]
think i'd rip my 2x8's as planned... and i'd rip some 7/16 osb 11" wide to match i'd use the osb on both sides maybe 1/4" shy of full coverage and nail it off on both sides with 2" ringshank nails... i think this would go pretty fast.... i might even use liquid nails on the 2x mating surfaces... just cause
p
Question:
Why isn't leaving the 7/12 pitch an option?
If it's an issue with the truss being to flat for the span, then I don't see how sistering 2x8's or splicing on wedges is going to fix that issue (although sistering seems better than the wedges, since the 2x8's would add some stifness to the rafter).
If it's simply an aesthetics issue, then do whatever you need to make the change - reminding the owner that he's paying for it.
Regardless, any modifications to an engineered product need to be approved by the truss company.
My idea for a fix is attached.
I presumed a 12" soffit overhang, and used a wedge sleeper ripped from 2x10 material, one 2x10 board required per truss.
In between acting as ties and top chord blocking, are members that fall on the plywood layout lines, and the ridge. They go between and are toenailed into both the sleeper and the truss chords. As you can see, the lowest is a 2x6, then go up through a 2x8 to a 2x12 at the ridge.
This should yield all the tying and tipover resistance you need.
Good luck, and tell us of the outcome.
Good Grief...I can't believe I wasted 5 minutes reading this...
Rip the wedges, nail/screw at the thin end, simpson clips at the fat, construction adhesive in the joint, sign off from the Archi. & the BI.....cheap, fast, & good-all three, when usualy you only get two......Puhleease......
I agree, but your frustration is an indication that you will not be a long time BT addict. Things get rehashed here ad infinitum, that's part of the fun.
Yeah, there's certainly no harm in trying to come up with different ways to approach this problem. Even though, in this particular case, it probably doesn't make much difference which approach one uses, someone may get a few ideas that will come in handy later. No harm in a little intellectual exercise -- too many mental "spare tires" around here anyway.
If ignorance is bliss why aren't more people
happy?
I come & go...just thought this post was as bad as some of the political shoving matches.....the smaller the stakes, the bigger the argument, sometimes...