When we built our house 8 years ago we had a small area of roof over our master suite that never got a roof vent.  I was told not to worry about it since it was a small area.  That area of the house has been much warmer nearly all the time.  Unrelated to that, our shower vent fan flapper always made a terrible racket in the wind and I was tired of it.  Over the weekend I had a roofer out fixing up some wind damage.  I also had him cut in a single roof vent at the peak of said roof.  Yesterday the sun was shining and I thought our bedroom felt different but it wasn't warm outside.  Today it reached 79 degrees.  Normally, our bedroom would be up to 77 or 78.  It was only 71 in there at 5:00.........I was amazed.....hopefully I'm not just imagining things!  I also ran some flexible insulated ducting from the shower fan to the new vent and screwed the other one shut......quiet.