"We built things this way thirty years ago, why are your designs so much heavier?"
a. for Wood ... We'll all the old strong trees are gone and we're left with much weaker wood.
b. for Concrete and Steel: My designs follow the current code provisions which have changed significantly in the last ten years alone.
"I've never seen designs like this in all my life."
What can I say, I'm an innovator or ... That's what they said to all the pioneering engineers throughout history... thank you very much!
"This 8" retaining wall has worked for thirty years and you want to replace it with a 12" wall."
Soil conditions vary from site to site. 12" is the minimum based on the site characteristics.
I don't know how polite and tactful this one is, but my old boss used to say it to contractors:
"Tell ya what, when you get your stamp, you can change it to what ever you want, have a nice day <click>"
...It was very effective.
Gerard Madden, P.E.
Middlebrook + Louie, Structural Engineers
71 Stevenson Street, Suite 2100
San Francisco, CA 94105