*
I’ve heard people talk about truss uplift with some vague reference to how drywall should or shouldn’t be attached to truss chords near interior walls. Anybody had any experience with this or is it myth? Please educate. Aaron
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Fine Homebuilding's editorial director has some fun news to share.
Featured Video
Highlights
"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.
Replies
*
Aaron,
It's no myth. I found out the hard way in 1988. The trusses in a home I built started rising in the middle, and where they ran over interior walls the ceiling corner joint split cleanly anywhere there was wallpaper(from where the tape was scored by the knife) and the rooms that didn't have wallpaper the corner tape was stretched and/or torn. In some areas the gap was as much as 3/4".
Imagine my surprise when the truss mfr. sent me a letter explaining "CPS"- ceiling partition separation. They aknowlege that it exists, they don't have a clear explanation why it occurs on some jobs and not others, but most of all they don't cover it in their warranty. Up until then I never heard of it.
Their only recomendation was to use drywall clips on the ceiling boards to make sure the drywall is attached to the top plate, and use no glue or fasteners within 18" of the interior walls, so that when the ceiling corner stays down with the wall plate, and the board goes up with the truss, there is at least an 18" transition for the drywall to bend, and not break. At the time, I asked a LOT of drywall subs about it, and none were aware of this requirement.
Needless to say, all of my jobs since then have included this detail. The phenomena is so strong, I am told, that if you attach the truss to the wall, it will lift the wall from the floor- that's why they don't recommend that approach.
This is just one reason why I am always recommending to contractors to pay attention to the fine print in product warranties, sooner or later you will get bitten.(Are you listening aj? ; } )
Hope this helps, John
*it has to do with the bottom os the chord being buried in the insulation.. and the top of teh truss being out in free air...they are apparently subjected to different moisture levels... and this is the favorite explanation for the occurence..
*There's quite a bit about truss uplift in the archives. try typing "truss uplift in the search function, and you should get plenty of info. Also - there is some info (and a couple of pictures) on Trussnet Look for the "Partition Separation" button near the bottom of the page. If you still don't find what you want, post back and I'll try to answer your questions as best as I can.
*Ron. those blinking pics of truss failure are too cool..we had a guy put up a whole roof for a motel in Newport, the whole thing collapsed... so they saved what they could and redid the roof... and it collapsed again... don't know what that guy was selling , but he sure could sell...he just went from one disaster to another.. still out there.. and according to those pics.. he has lots of company...
*Is it standard practice to fix your plasterboard directly to the underside of the truss chords??That has ben outlawed here for a long time as poor building practice. We have to batten (fir?)out the chords first then fix the board to that. It also eliminates the separation you are talking about here.
*Mike - unfortunately, truss collapses are all too common. I've personally been involved in one where 9 guys went down with a set of trusses. That subject has also been covered in the archives to some degree. You might try searching on "bracing" if you're so inclined.
*Mark... yes it is standard practise to fasten board directly to the bottom of the trusses.....except in a large part of New England....here, the common practise, except in tract housing and some of the "value engineered" houses, is to fur (i always want to say "firr" but the building dictionaries say "fur" is the accepted) the trusses and rafters down with 1x3 furring @ 16" OC...i think it makes a better ceiling and it certainly facilitates wiring, and is an easier "target" for the rockers..interesting that it would become code in your jurisdiction... do they have a line of reasoning for that ?and also interesting that you say it MAY prevcent the effects of truss-uplift... i've always furred my ceilings , wether rafters , joists, or trusses.. and i've never experienced truss-uplift... i wonder if there IS a relationship....Ron, do the truss mfrs. have any insight into this?... as far as furring the ceiling helping to prevent "truss-uplift" and also how it may or may not strengthen the roof assembly?as far as bracing goes... we've had this discussion before.. all our trusses are pre-engineered and the bldg. inspectors want to see the P.E. stamp on the truss plan, submitted with the original plans,.. and the bracing is always reviewed and is part of the inspection....at least it is in the 4 or 5 towns we work in ... and they all go to the same state bldg. comissioner school, so i know that is where this point is comming from...
*This months' issue of Walls & Ceiling Magazine has an article by Joe Lstiburek that addresses wood movement, truss uplift & drywall attachment. His explanations is same as Mike Smith's above. Good article, excerpted from his book "Builders guide to cold climates." Joe H
*Mike,I think it originated with the problem of nail popping in ceilings ( though everyones screws here now. Plus firring out gives a much neater ceiling plane and finish for the board. However as a bonus the code now accepts the battens as replacement binders for bracing, ( there is no doubt in my mind that it presents a much more rigid ceiling plane area.).We too have to present all the truss doc. at frame inspection.
*Mike - I don't know why furring the bottom chord of the truss would affect truss uplift any. The truss will still move, and the drywall with it. The only way I can see it making a difference is if the furring strips weren't really close to the walls, and some "flex" was allowed in the drywall. I doubt it would strengthen the roof assembly any, as the bottom chords are basically in tension the vast majority of the time.
*Ron, As a P.E. you may know better..my understanding is it helps create a ceiling diaphragm. As for uplift, we run our battens right through intersecting walls ( ribbon plate on externals to jack up the height) then pin our top plates to the battens. we never have trouble with movement, and we always use plaster cornice so if there was movement it would crack there first. ( it doesn;t crack)
*I thought I would add that the ceiling partition separation I described above is seasonal. It goes up when the heating season goes full swing, and goes back down in the spring. And this cycle continues after 12 years. The attic is well ventilated, and the insulation is blown fiberglass, R38. Furring the ceiling would have made no difference, unless the furring was somehow attached to the walls, rather than the trusses, at the partitions.Also, I was told by the truss mfr. this occurs in only a small percentage of cases. There is no "common denominator" to predict what jobs it will occur on. Lumber salesmen are very aware of it, but I have talked to a number of builders who have never experienced this and have taken no precautions to prevent it.John
*JRS - I believe all truss uplift is seasonal. I've never heard of any that was otherwise. I've heard that 75% of uplift cases only happen once, and they never do it again. But that doesn't bear out with my own experience.The only common denominator I've seen in uplift cases is lack of ventilation.
*Hi guys.I thought I'd share something with you regarding a solution for truss uplift. We would put 2x4x16'next to the trusses and nail the ends only. We would do this for the trusses over partition walls,hallways etc.The trusses weren't nailed to the plates allowing them to move accordingly, but the 2x4's were nailed to the plates.The strapping was then nailed to the 2x4's only.This allowed the drywall on the ceiling to remain bonded with the walls. Hope this makes sense.Harley
*Harley.. i think i see what you were doin.. but those sliding clips that Simpson sells do the same thing...what's the benny?.. so you get a ceiling corner?help me out here..Al e. Newman
*Ron,The sight you sent us to gives five reasons for partition separation, only one of which is seasonal.Here they are: 1)Building settlement(improper or inadequate footers)2)Inconsistant framing practices3)Moisture effects of the platform and wall construction(I took this to mean using framing with a very high moisture content that eventually dries out)4)Deflection of the floor5)Truss arching(bingo-I think that this is what we all are talking about) They state that only 20% of all partition separation is caused by this!The two largest truss mfrs. in my area have told me that there are no common denominators, and that partition separation affects about 2% of all truss jobs, industry wide. Back when I first contacted the truss rep about this job, I asked him if it was a one time occurance, and he told me to expect it to go up and down every year. Unfortunately, he was right.John
*Mark & Ron... we do the same thing.. we furr as soon as the ceiling /roof is up... BEFORE we build partitions.. so there may be just enough flexure in the ceiling diaphram so the "truss uplift " is not noticed...GeneL does the same thing basically with his sheetrock..... he runs all his sheetrock BEFORE he builds partitions.. he doesn't furr (at least i don't think he furrs his ceilings) so maybe this flexure helps prevent the effects of "truss uplift" there also...never seen it on any of our jobs.. and we've always used a lot of insulation, and a lot of scissors truss, etc....keep our fingers crossed too
*JRS - You're right, of course, about what they say at Trussnet about the "5 causes". I don't know what their research is based on, but I don't think those 5 reasons are all that accurate. I think that whomever wrote that was a "spin doctor" for the truss industry trying to deflect criticism away from the truss uplift problem. I guess I would say if you have cracks all year, it's not truss uplift - If you only have it during heating season, it is. The 2% rule of thumb you mentioned sounds reasonable. It doesn't seem to happen all the time. But, as I said yesterday, every case of truss uplift I went out to look at had bad ventilation or no ventilation at all. I don't claim to be an expert on the subject - that's just been my experience. I think I relayed a couple of those stories - they may be somewhere in the archives.
*Joe Hennessey. I was about to post when I sawe your post. For those who don't subscribe to Walls & Ceilings, the article by Lstiburek can be gotten on the net at http://www.wconline.com. The title of the article is "The Big Chill." GeneL.
*Mike, The strapping I'm referring to your guys furring.Where I am in Atlantic Canada,a lot of guys don't use those drywall hangers.They don't like them. Here's a dumb question.What's that ceiling corner your asking about? Thanks, Harley