Ceiling cracks

[Jerry Simon]

My drywalled basement ceiling, approx. 27' x 13', applied to TJI ceiling trusses (upper and lower rails separated by OSB).  Two drywall seam cracks, four feet apart, running entire 27' length of room, cracks perpendicular to trusses.  Zero noticeable flex to floor, and minimal live loads above, and minimal dead loads, biggest being a refrigerator at middle third of span.

I could see having these cracks if they were running parallel to the trusses, where just a couple flexing trusses could cause cracks, but hard to envision cracks running entire 27' length of room when cracks are perpendicular to trusses.  In my mind, it would mean almost each and every truss would need to flex, more than a little, to cause such cracks.

Any thoughts at what else might cause these two, four-feet-apart, parallel seam cracks aside from truss flexing?  Could just one, or a couple/few, flexing trusses cause such cracking across entire 27' ceiling span?

[Tom Raymond]

It's not the framing that's moving. You most likely have mesh taped seams. They always crack.

 

[Jerry Simon]

1 hour ago, Tom Raymond said:

It's not the framing that's moving. You most likely have mesh taped seams. They always crack.

 

More than just cracks; big-a** splits I should have said.  And, this is just half of the basement ceiling; steel beam divides room in half, and cracks are only on the one, same-size half (room is about 27 x 27).

Would like to fault contractor, but seeing above, hard to make that case.  Pretty sure I'm missing something, though.

 

[hausdok]

If my memory is working properly, I seem to remember that these things are allowed to sag more than 2X. 

Many years ago I had an issue where I found that a local builder had been mixing truss joists with rim joists of regular lumber. The truss joists were custom made for that builder to the same nominal dimension of the joists so he wouldn't have to rip the rims to get them to the same initial height. The builder tried to sue me when I reported it in a number of houses he built The late JD Grewell had helped me with that case. According to the TJI manufacturer and what was called the Truss Council back then, even a 1/8 inch difference can result in damage to a home. I seem to remember J.D. had written extensively about it because he'd discovered homes where the trusses has begun splitting when placed under differential pressure. I'm not clearly picturing what you have there in my head, so maybe I'm full of s*** as regards this one.

[Jim Katen]

When was the drywall installed? 

[Jerry Simon]

23 hours ago, Jim Katen said:

When was the drywall installed? 

About five years ago.   Don't recall timing of such related to cracking appearance, though.  That said:

Above half the crack-affected area is my master bedroom, and I had carpet removed and hardwood flooring installed in the bedroom a couple years after the drywall went in.  Thinking that could have easily caused the cracking (though may not explain why cracks run entire length of ceiling instead of just below the bedroom area).

[Jim Katen]

It really doesn't seem like much of a mystery. The TJIs flex a lot and the drywall finishing was crappy. 

You can order TJIs that can easily support a given span with regard to "bending" but be entirely inadequate with regard to "deflection." When I built my office, I purposely specified TJIs two notches up from the prescriptive size just to reduce deflection. Those suckers flex a lot. 

On the same job, I hired a great drywall finisher, who, unbeknown to me, sub contracted the work to Goofey & Pluto. They embedded all the tape in topping compound. For the life of them, they couldn't understand why I went ballistic. 

Scrape down the broken joints and re-tape them with hot mud. 

[Jerry Simon]

20 hours ago, Jim Katen said:

It really doesn't seem like much of a mystery. The TJIs flex a lot and the drywall finishing was crappy. 

I would 100% agree and would never have questioned it, 'cept for the fact that the adjoining, same size ceiling area (the other half of the room separated by the steel beam), didn't show nary a sliver of a crack.

Those suckers flex a lot. 

100% agree.