The Z Wall Shutter System provides an effective backdraft prevention system which overcomes all the weaknesses present in other systems. The Z Wall uses a concept of a double shutter, but instead of just a 6" gap between the 2 shutters, it provides a deeper "airlock" chamber between the two. One fan, either one of the ventilation fans, or an additional small continuous operating fan, maintains constant negative pressure between the two shutters. Any air that leaks back through the fan shutter is trapped in the airlock chamber and does not have an opportunit to leak farther through the second shutter wall. The Z Wall is not adversely affected by wind and is highly reliable in preventing backdrafts.