Long (debit) vertical spreads do not have a margin requirement; they just need to be fully paid for.
 

example

For example, in order to buy the following spread, you would need $35 in your account to fully pay for the spread.

  • Buy to open 1 ABC 100 Call for $1.40
    • 1.40 x 1 x 100 = -$140
  • Sell to open 1 ABC 101 Call for $1.05
    • 1.05 x 1 x 100 = +$105

Net Cost: $105 - $140 = -$35