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Ceiling Drywall Cracks

Ceiling Drywall Cracks

Ceiling Drywall Cracks

(OP)
I have a client that is experiencing truss uplift at a number of interior walls.  Prior to seeing the condition the wall had been rigidly clipped (rather than a slip connection) to the trusses to "prevent" the movement between the trusses and wall.

After the clips had been installed the owner noticed long cracks in his ceiling running perpendicular to the trusses.  The worst crack occurs at the center of the building.  This sure sounds like truss uplift to me but the truss supplier feels it is a sepparate condition. I haven't been able to find any cases of truss uplift causing cracks in the middle of the ceiling, only at interior walls.  Also could rigidly attaching the wall to the trusses cause the long ceiling cracks.  Has anyone else ran into a similar condition?

RE: Ceiling Drywall Cracks

In that the interior walls were originally rigidly attached to the trusses, the structural behavior of the trusses has been modified with the addition of an interior support for which they were not designed.  The deflection of the trusses was less under load.  

Now, with the clips, they have to span the full length, for which they were designed, but they may have developed a deflection memory with time, due to the original support condition, that could, at least in part, be the reason for the cracks.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Ceiling Drywall Cracks

What is the mechanism for the uplift?  Is it shrinkage?  Is it wind?

Usually when cracks in drywall occur, unless there has been a significant wind event,it can be attributed to drying shrinkage of the materials, including the gypsum materials and the trusses.

Agree with Mike on the support conditions...that can screw things up.

RE: Ceiling Drywall Cracks

(OP)
I believe the mechanism is the phenomenon known as truss uplift where there is a difference in moisture between the top and bottom chord which causes the bottom chord to arch.  Typically it is seasonal, the difference in moisture tends to occur in the winter.

RE: Ceiling Drywall Cracks

You might check w/ the Truss Plate Institute (TPI) - google it.  They have info on this subject and can point you to other sources.

RE: Ceiling Drywall Cracks

Truss uplift, from what I have seen is definitely seasonal. I have seen this in many homes, including my own. Every winter, I see where the drywall corner tape in one bedroom starts to pull away from the corner, by this time of year it is nearly invisible.
Also I have noticed that as the bottom chord arches in large wide open ceilings, cracks in the drywall perpendicular to the truss direction can develop especially if a long seem in the drywall happens to line up near the splice plate on the bottom chord.
When building homes we tried to avoid this where ever possible. I have seen no documentation on this other...just my own observation as I don't believe gang nail plates keep the splices firmly together under movement.  

RE: Ceiling Drywall Cracks

I did not experience truss uplift when I lived in Florida but I moved to NC and it was very prevalent the change occurred with the change of seasons.  I believe it is both temperature and moisture differentials.  I started floating the ends of the drywall.  the drywall was not nailed within 12" of the interior partitions.  I saw this in an old manual by USG.  It works!!  This is also a good idea for wall drywall install the first wall and nail install intersecting wall and float,  The tape joint will not crack but floats.

RE: Ceiling Drywall Cracks

bylar...good suggestion.

RE: Ceiling Drywall Cracks

Good thread. You want to consider installing a metal furring channel that 'flexes'. In Ontario Canada we call it 'resilient channel', only one side is screwed in, allowing it to flex. I actually used this is my own house (which has a large span truss system) 5 years ago. Not a crack. Check with a specialty drywall/accoustic supplier.

RE: Ceiling Drywall Cracks

RE: Ceiling Drywall Cracks

(OP)
Thanks to everyone for sharing your knowledge and experience on this topic.  I really appreciate it.  You have all been very helpful.

RE: Ceiling Drywall Cracks

stickmotion- that was a great article, added it to my library. I have seen similar but that was on point.

Have this exact same condition in the second story of my house in Florida, The drywall was all replaced right before I moved in, and about 4-5 years later it began to crack along the joint tape at the interior wall-ceiling joint.

I also see this type of cracking constantly at wall-ceiling joints at interior and exterior walls while doing residential inspections, but usually it is pretty minor.

Another solution since its non-structural is crown molding that hides it!

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