Erwin:

You really aren't forthcoming with much information, but here's my take on it. If you are being called as an expert you will want as much authority on your side as you can muster. The model building code is one good thing to have in your camp in theses circumstances. Without that reference you will be relying solely on your opinion, "customary building practices in your area", of the AHJ's (usually) uneducated guess at what's correct.

IRC N 1102.1.7 states in part "The exposed earth in all crawl space foundations shall be covered with a continuous vapor retarder having a maximum permeance rating of 1.0 perm [(57 mg)/(s · m2 · Pa)], when tested in accordance with ASTM E 96."

Go to: Plone —
Look up the info based upon the area of the country you're in. Joe Lstiburek, Ph.D. and Nathan Yost, M.D. have good crawl space info on this site.

Also try IBACOS: Integrated Building and Construction Solutions, Forest Products Laboratory -- Forest Service -- USDA, U.S. DOE Energy Efficiency and Renewable Energy (EERE) Home Page, ad infinitum.

Don't go to court half-cocked.

Aaron