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RE: Drift

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John:
 
As you probably know, few codes or standards address drift limitations.  I work in seismic zone 1 (Denver, Colorado), and we therefore limit our building drift to account for a desired building performance due to wind loading.  For wind drift on buildings we typically limit those values from 0.0015 to 0.0035 times the building/story height, and simultaneously limit seismic drift to a value of about 10 times greater (0.015 to 0.035).
 
As in the case of your auto dealership, I concur with the previous response from another, that the window manufacturer or architect can provide information on how much movement the window can tolerate within the frame.  We often ask this question when designing office buildings to determine how much beam deflection to allow.  The typical response is that the window can move about 1/2" within the window frame.
 
If you have a higher risk of an seismic event than we do here in Denver, than I would suggest you consider designing your structure to account for drift due to seismic forces with (0.0035)*(H) being your maximum allowable displacement.  In doing so, you should have covered drift requirements for daily loadings such as wind/gusts, and still have a sound structure after a seismic event.
 
Bill S. Marczewski
Denver, CO 80210
bmarczewski(--nospam--at)martind.com