This Kentucky source indicates a frost line of 30", but you would still
be best asking the local practices from the local building inspector, as
frost lines can vary. The frost line is more or less arbitary, but is
intended to cover most years. In a really cold year the frost can go
lower and freeze pipes.

http://www.crestviewhills.com/pdf/checklist_decks.pdf

Richard


wrote:
I am goign to build a pole barn. I need to extend the posts 6 inches
below the frost line. How do I find out what the frost line is for my
area?