Vertical deflection allowance: where do you draw the line?

[Geoffre14]

Imagine a partition wall below a long-span truss with expected deflections of 1/2" up or down. Often us Structural Engineers will specify deflection clips or similar methods to allow for this truss' deflection.

Now imagine a single-family home 2 stories plus basement. Roof rafters' expected deflection might be 1/4". Partition walls might not align all the way to the slab-on-grade basement slab. Often these walls are built tight between floor and ceiling. Should we be spec'ing deflection allowance? From what I've seen, it's not really common practice, which means some partition walls will wind up transferring weird gravity loads to other parts of the building / other floor joists / etc.

Where do we draw the line? Why do contractors furrow their brow when I bring this up? Can anyone provide some guidance, rules of thumb, or their guidelines for dealing with this?


(PS Just made up those deflection numbers for the sake of argument. This doesn't pertain to a specific project.)

 

[XR250]

I have never worried about this in a house and have never had a problem (that i know about). I have inspected over 1000 houses and have never witnessed a problem I could attribute to this.
On commercial jobs with metal studs, I take care of it.

 

[chicopee]

Since a partition wall is not a bearing wall, there must be some flexibility at nailed joints so that no crack is occurring in the partition wall. Although in older wood frame houses where walls of wood or steel lathe with plaster, you will notice cracks if there is no wall paper covering. Whether these cracks are from settlement or beams deflecting, it is hard to tell.