I agree with @tim that normalizing depends on content.
I've written up what I call a "style sheet" for our team. It's guideline of how certain effects should be normalized. It's not rigid, purely a starting point, but is something like this:
- Specifics: -10 to -3 dBFS (door knob
moves on the low side, gunshots on
the high end)
- Atmospheres: -12 to -8 dBFS (birdsong
on the lower end, traffic higher)
- Wind: -15 to -10 dBFS (higher end for
the gusts or piercing whistles)
- Room tones: -15 dBFS, sometimes lower
We usually discard any sound below -15 or -20 dBFS as it is too quiet or hissy to be useful for our projects.
Of course, it all depends on the content, and how you like to use it. Each effect's level is customized.
Whichever your choice, avoid normalizing everything to the same level. This is murder to audition: wind will be the same level as a metal crash or jet pass.