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I added a 10'x15' room and am preparing to hang drywall when I noticed the center of the engineered roof truss (15' span) is sagging slightly. The 2x4 trusses have a joint in the bottom center. If I put a 4' straight edge on one side, the gap about 3 foot out on the other side is ~1/4".

Talking with some friends we disagree on how to hang the ceiling drywall. Should the joint line up with the center of the truss or should the panel cover the center? Which would reduce the chance for cracking?

Note: Images are exaggerated for clarity.

Option 1: Joint in center

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Option 2: Overlap center

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    Wow! I am surprised on a 15 foot span they would make a joint in the middle. They have never heard of 16 foot 2x4's? I would never put a drywall joint anywhere it is likely to crack. (The pros on our job sites put a full sheet over a door and then cut it out just to avoid a joint along the door frame.) If you put a joint at that location I would bet you will never get it to survive a year's worth of weather without cracking. Just my humble opinion.
    – ArchonOSX
    Commented Sep 20, 2017 at 16:17
  • @ArchonOSX - Agreed, I was pretty surprised myself to see that joint when they were delivered. This was my first time ordering trusses so I just assumed it was common practice.
    – Automate This
    Commented Sep 20, 2017 at 16:45
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    I'd be taking a hand planer and flattening things out (1/4" doesn't concern me a bit), and then I'd maybe sister a 2x4 with glue and screws to prevent movement if it seemed prudent.
    – isherwood
    Commented Sep 20, 2017 at 17:30
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    Before you drywall, I would consider jacking the trusses up until even and adding angle iron across those gaps. Or some other reinforcement scheme as isherwood said. I take it there is no going back now that you are this far. You can only reinforce the trusses in place.
    – ArchonOSX
    Commented Sep 20, 2017 at 18:06
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    @ArchonOSX - Yep, no going back. Fully roofed, sided and painted (outside). Got it weather tight before moving to the inside. Sounds like a plan, I'll jack up, add supports, and plane bottom side if necessary.
    – Automate This
    Commented Sep 20, 2017 at 18:35

1 Answer 1

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Your trusses are defective and done very wrong and would only be used atop columns, supporting beam or bearing wall. Call the truss manufacturer for replacements that are built right, solid and seamless sticks on the bottom.

Sagging before even installing the drywall's load is a disaster ready to happen!

After that correction, then you can put your drywall joint on the truss for very wide butt-joint treatment. Or even better is, to put your joint between trusses and very shallowly "V" back-blocking framing for a tapered treatment.

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  • Heard back from truss manufacturer last night. The design was intentional, but they offered new trusses. Since I'm already closed in they'll send a rep over next week but said the fix would most likely be adding full length 2x4's under the truss to even it out and thus lowering the ceiling 1.5". We'll see what they say when they see it.
    – Automate This
    Commented Sep 23, 2017 at 15:05
  • Phew, I'm glad to hear you might live another year. I do love the response though. Yeah, um, we meant that, but we'll be over ASAP just to tidy it up for the movie...that you're widow will be showing in court next year. Happy its going to work out.
    – Iggy
    Commented Sep 23, 2017 at 23:50

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