Roof Truss Manufacturing Tolerance

[Mattilac]

Question for all the experienced framers on here.

I'm building a garage with roof trusses (40' span, 8/12 pitch). Main build thread here. I received the trusses about a month ago and am now finally ready to start installing them, but I've noticed they have some deviation in overall width and height. Everything I read online indicates that the trusses should be damn near identical to one another, but I'm seeing differences as much as 1" in either width or height from truss to truss.

I'm curious what is generally acceptable? Do you ever make adjustments (plane down or shim up) before sheathing?

I know... we're not building pianos here, but I'm afraid to just sheath it and then discover it doesn't look flat and that I should've 'worked' it some. Maybe you veterans have some insight.

 

[Zen]

I bet by the time you get them on the structure they will all be pretty equal. I'm guessing with all the movement from building, shipping, storing that they "moved" a bit.

 

[Spud McGee]

Are they supposed to be matched up? Looks like you have the main bodies and then the tips separate.

What if you match your tallest main truss with your shortest peak and your shortest truss with the tallest peak? How close are those?

As far as width goes, I say you have them all standing up and stacked already. If the gap between the widest and narrowest one is 1 inch, and that bothers you, leave them stacked up and cut a quarter inch off the longest one on each end. Now all your trusses are within half inch of each other, and about half of them are identical length.

 

[Rusted Nut]

Half inch variation is common, an inch could be a problem. I would call the truss supplier.

 

[Wolley]

On a truss like that, where do you line them up when you are installing?

 

[nadogail]

You need a bundle of shingles for shims when you build a house.

 

[mike93lx]

After letting them sit for a month, I bet you will be SOL with the supplier.

I'd install and tweak as needed. A hand planer and some strapping will get it there

 

[MovingAlong]

The folks at the Structural Building Components Association have some information on Allowable Variances In Trusses..

 

[wssix99]

I received the trusses about a month ago

I'll bet that they were identical when they came off the jig and have changed shape since then, over time. Particularly, with all the different types of members in the truss, every piece of wood is going to dry slightly differently and the pieces are going to shrink different rates.

I like @mike93lx suggestion and would sort them by size and shave/shim, as needed, to get the roof straight. Once you get them in permanently in place, they should stop their wild differential movement.

 

[oldcarpenter]

I would install them, shim between wall and bottom cord as needed. String line the edge of flat top.
Shave or add to top cord as needed. Get it the best you can, it is going to be there a long time, and you will look at the dips and bumps every time you approach it.

 

[Firebrick43]

Are you measuring from the ground to the top chord?

Or are you measuring from the bottom chord to the top chord

Trusses will lift in the winter when they dry out, and straighten out in the summer when humidity is up. Your storing them out side for some and even if tarped its going to play hell with the lumbers MC.

As you dry it in and the lumber drops and reaches equilibrium things are going to move again.

 

[antman213]

I've had bad luck with trusses, seems they aren't as perfect as they should be. We worked it out in the field in each case but I would have thought they should be perfect. Worst we've run into is deviation from back chord to front (it was a square truss with parapet sticking up) up to 1-1/2". also squareness isn't always guaranteed or the same between different trusses

 

[bb29510]

they are made in jig, but after you finish installed them you will never look up there again
just dont use strand board or you will have a crooked roof

 

[karoc]

I purchase 38 trusses 5/12 x38’ length from Allied Trusses. Looking at their website, it is top notch. Was I ever wrong, same as you the height varies and location of plates sizes was a mix match. Quality of wood wasn’t fit for making pallets. Enough of my experience, take what you get and make repairs if needed. I was on my own with Allied

 

[Hank11]

It appears that width wise you have enough to trim to a perfect string line. I would shift each slightly side to side to get the best compromise fit on the upper chords and then trim the ends. You have to trim the ends anyway.

For the the piggy backs, it looks like they are designed to sit on the ends of the upper chords and have a little bit that can be trimmed to make a better fit. The crew will be cussing you and the truss company the whole time.

Or you can just throw them up and let it be. Although an inch between two adjacent trusses is a lot. I'd hate that.

I just did similar but smaller trusses and the tops (piggy backs) were numbered to go with each main truss.