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Cracks in drywall ceiling which are attached to trusses

Cracks in drywall ceiling which are attached to trusses

Cracks in drywall ceiling which are attached to trusses

(OP)
I have inspected several houses that have been damaged by falling trees and by wind loading from tornado force winds (90+ mph).  On the houses that have a wood trussed roof, I have found hairline cracking in the drywall ceiling joints at the interior of the ceiling.  These cracks do not occur around the perimeter as with "truss uplift".  I have attributed these cracks in the ceiling to the excessive loading and the natural downward deflection of the bottom chord.  Any thoughts?   

RE: Cracks in drywall ceiling which are attached to trusses

Is the cracking random/angular or do they align with sheetrock panel-butt seams?
Are the trusses longer span or scissored (less stiff) which would deflect more with your dynamic loads?

RE: Cracks in drywall ceiling which are attached to trusses

(OP)
The cracking is uniform in the sheetrock panel-butt seams.  The trusses vary in length from 30 to 40 feet.  I think they have all been fink trusses.  Top chord pitch would be between 4:12 and 6:12.

RE: Cracks in drywall ceiling which are attached to trusses

Deflection can be both up and down.  The max deflection typically occures miod-span.  I have seen excessive deflection in the field at the butt seams too.  We repaired with fiberglass tape and re-mudded then finished the clg.  

Check the top and bottom cords for cracking, and if the truss sheets are available the correct bracing and connectors.

RE: Cracks in drywall ceiling which are attached to trusses

(OP)
Thanks for the comments.  Its nice to know someone else has had the same experience.

RE: Cracks in drywall ceiling which are attached to trusses

I think the reason why it cracks at the drywall is due to shear reaction that was transfer by the truss connecting to the walls. now here is the idea, if the truss support joint doesnt have any base plate to distribute the reaction to the base plate the tendency of that is to have a shear crack.

RE: Cracks in drywall ceiling which are attached to trusses

I realize this is an old thread, but what the hell.... I've been designing trusses for 5 years, and I had never seen this, untill it happend to me. I was sitting @ home during the last hurricane (I live in florida, block house, wood trusses)and during the peak of the hurricane my ceiling began moving in a way I can only describe as a breathing effect. When the wind picked up it pushed down, when it eased up it returned to normal. I believe this was the wind entering the attic thru the ridge vents, (I also got some water), this caused a rapid pressure change in my attic, that was caused by the wind, and resulted in a balloon, or breathing effect. It is my belief that because sheetrock is semi-flexible, and mud is not, it cracked it @ the seems but left the sheetrock undamaged other than the previously stated water damage. I'm willing to bet your seeing the same thing.

RE: Cracks in drywall ceiling which are attached to trusses

(OP)
Thanks for the info.  It makes a lot of sense.  I never thought about the pressure created inside the attic.  The pressure as well as the movement in the trusses would certainly explain the cracks in the ceiling drywall.  Thanks for your first hand account.

RE: Cracks in drywall ceiling which are attached to trusses

Glad I could help.

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