Big Jim wrote:
If you want ventilation get a fan. More insulation is always good



The problem with a fan is that it must exhaust massive amounts of air to be
effective. Assuming an 1800 sq ft house with a 6' attic at the peak, we're
talking (roughly) 6 x 1800 x 0.5 = 5,400 cu ft. An attic exhaust fan should
change the air every 2 minutes, so you'll need a fan that moves 2,700 cu ft
of air per minute. That's a good sized fan.

"For well-insulated ceilings (i.e. insulation levels of R-19 or above) it is
doubtful that a power ventilation can be justified economically. "

http://factsfacts.com/MyHomeRepair/ventilation.htm