drywall and trusses - what variation is acceptable?

[jpcjguy]

Hi all,

So I am nearing the insulation and drywall stage of my detached. I have 4/12 inside pitch scissor trusses over the lift bay. They are 19.25" on center.
I was noticing the good amount of sway there is in the bottom cord of the truss. I can move them back and forth pretty easily. I can run 2x4s across them perpendicular on bottom cord to make them more rigid, but then it makes insulation more of a pain. Plan is to staple kraft faced R38 or R49 between the trusses.
On another note, when I held my 4' level across the bottom of some of the trusses they were not all flush. One or two was 1/2 - 3/4" lower than the others. What is the acceptable level of variation? I don't want to hire a drywall crew and have them install it and have it be all wavy - and then give them the excuse that the framing was off, so it is not their fault.

 

[readhead]

The truss plan will show all of the bracing including the rat runs, or what ever they may be called where you are, on the bottom cords to stabilize and maintain the spacing. They need to be installed. As far as the out of plane problem you can strap and shim the whole lid or sister the bottom cords with 2x4. I would opt for the latter.

 

[Bogie1632]

Is it acceptable to you is the real question. You don't want it wavy so shim them. I try to stay under 1/4" myself. Lots of ways to do that but they do sell shimming material just for this or you can run some strips from a 2x4 out on a table saw yourself and staple/tack up. Sistering is fine too but always seems to me to be a waste of materials. Since your ceilings are pretty high your not likley to notice that amount of variation and once the board is up you shouldn't get any deflection like your getting now when you push or pull on the bottom cords. If your going for a finished look use paper tape on the joints, not the mesh. Paper is much stronger.

Good luck.

V/R
Bogie

 

[spudley]

As others said, I'd shim using Bogies plan. But I'd also have a talk with the contractor or truss mfg, that is if the trusses were designed for bottom chord weight, which should be listed on the truss plan as dead load bottom chord.

 

[ssdave]

Brace the trusses per the truss manufacturers recommendations. That will keep the spacing uniform.

Then, just sheetrock it. You're overthinking this. That variance will not be seen in a high, scissor truss ceiling. That's within normal manufacturing tolerance.

 

[Bigblockyeti]

3/4" variation on the bottom of a truss sounds like a truss problem and would be completely unacceptable. At this point returning it (them) for properly manufactured trusses that have passed some symbalence of QC is too late. I would certainly contact the truss manufacturer and see what they recommend then invite them to pay for what has to be done due to the lack of quality in their product. If you drywell right over the trusses as is, it will look terrible.

 

[karoc]

1/2 or 3/4 I don't think your going to see if from 12' or 14' away. Over time the wood is going to move,but I would at least put some straping to at least get them all space apart correctly so that when you do sheetrock all will be on correct center to center. Heck your slab or maybe the framers are off little. No worries go for it
Guessing these trusses are not home made but engineered.

 

[jpcjguy]

Thanks for the feedback everyone. I have not String lined it yet but will - what I saw was a sample when I was doing the finish framing on the end wall. They were engineered trusses that were delivered.

 

[MushCreek]

My trusses for my house were that bad. I shimmed the entire ceiling, which was a lot of work, but my ceilings are perfect. If my shop were drywalled, I'd do the same thing, but I'm an OCD retired tool maker. There should be braces for the lower chord. It will be on the drawings from the truss plant. They NEED to be there; they're part of the structure. If you strap them with 2X4's and fasten them well, that should be plenty of bracing, and you can do the strapping after you put up the insulation.

 

[NUTTSGT]

No bracing on the bottom chord of the trusses ?

I'd guess those two trusses out of whack got turned around end for end when they were put up.

 

[CraigStu]

I'd be concerned w/ weight if you sister a bunch of 2x4s up there so I'd shim.

 

[sierradmax]

You should have a booklet on the truss design that shows lateral bracing. Also, that 2nd scissor truss inboard from the end wall looks as if it's not sitting on the wall, which could be the reason why your bottom cords aren't even. Run ferring strips and shim with plywood. Use screws in lieu of nails to attach ferring.

 

[3pedal]

I would have the truss manufacturer come take a look. Occasionally framers will put a truss in backward or something else can happen damaging the truss. They should be able to verify if there is an issue. If there is, they can work with their engineering team to repair the truss in place many times, instead of tearing it out.

The lateral movement of the bottom cord is interesting. The truss plan will show if there is supposed to have lateral bracing. Sometimes you do, sometimes you don't.

 

[DTE]

I have always stripped builds with 1 x 4 boards 16 in oc. Little more cost but better results.

 

[tros]

I did not see any bracing from the end wall back out 4 trusses on either side . This will help with the end wall moving we did that in ours now the wall is stiffer .When we drywalled it got really stiff hope this helps you out

 

[csp]

At this point returning it (them) for properly manufactured trusses that have passed some symbalence of QC is too late. I would certainly contact the truss manufacturer and see what they recommend then invite them to pay for what has to be done due to the lack of quality in their product. If you drywell right over the trusses as is, it will look terrible.

The trusses may not be the issue. This could just as easily be an installation issue, or outside walls they are installed on that aren't parallel the entire length of the building. A top plate that's not flat and level for the entire length is another possible cause. A combination of any or all of these could also be considered.