wavy drywall ceiling 2

[PSUengineer1]

I have a cathedral drywall ceiling that is wavy. The waves (downward deflection of drywall) appear between bottom chords of scissor trusses. Slope of the roof versus the ceiling (5:12 vs. 2:12). No cracks (transverse to truss spans) are present in the drywall ceiling. No soffit ventilation at eaves. No visible signs of strucutral distress or defelection in the form of cracks in drywall wall and ceiling surfaces.

Here is what I thing is going on: Moisture from condensation over time has softened the drywall ceiling causing it to sag. Moisture Is from inadequate ventilation of the cathedral ceiling. I prefer not to opine on thickness of drywall; but it probably is not thick enough.

Any thoughts to share? Are you on board with my thought process?

Thanks,

 

[XR250]

I agree with you on the moisture issue. 24" O.C. trusses and standard 1/2" drywall probably ain't helping either.
Maybe they used 3/8" drywall?

 

[jayrod12]

Most of the builders I know mandate 5/8" drywall on ceilings to stop this exact thing from happening.

 

[PSUengineer1]

thank you. I have all I need here.

 

[XR250]

Most of the builders I know mandate 5/8" drywall on ceilings to stop this exact thing from happening.

you don't know enough builders :>

 

[jayrod12]

you don't know enough builders :>

Oh I know of lots that would go to 1/2", but we try and avoid having those ones as repeat customers. The trick is to notify the architect of the potential issues in the first meeting and persuade them to spec 5/8" at the start.