Urathane Insulation in Basement (Spray Foam)

[JRH]

I am finishing a basement and was planning on using the Icynene product or something similiar for the walls. It is a spray on foam. My question is how far down should I spray the walls? I have heard 36" down to all the way down. I have 9' ceilings in the basement. Some have indicated that I do not have to go below frost line. This is located in Bardstown, KY, 30 miles south of Louisville. I will be using the closed cell spray material.
Thanks for any help.
JRH