Rat wall questions
 

Well I have forms up and 3 yards of sand coming tomorrow. The person I
talked to at ready-mix plant told me to put down a minimum 3" of sand. so
now my I am hearing that I need a rat wall......my brother says to dig a
trench down 18" The ready-mix guy said 10" 18" sure seems like overkill
to me....The building inspector did not mention anything about a rat wall
and he is away this week so can not ask him... If I do dig out this rat wall
should I do it before sand or after sand? and does it really have to go down
18"? TIA