Ventilation is not always the answer. In fact, at times it exasperates an existing problem. Increasing ventilation is not the "Holy Grail" of attic problems. At times (And the situations are limited) to correct a problem, I have elliminated ventilation in a given area.
Most attic ventilation is based on inducing an air flow in your attic by creating what is many times referred to as a "Chimney Effect". By having venting at 2 different elevations. Air flow is caused by the warmer air rising & exiting our the high vents. The resulting negative pressure that this produces in the attic draws outside air in through the lower vents. However, if there still remains the leakage of living space air into the attic, the resulting negative pressure will draw from there because it is the path of least resistance (The warm air in the house also wants to rise. This means that it has a positve pressure. The outside air's pressure is neutral.). Therefore, until the source of the problem is corrected, adding more ventilation is not the answer.