I have an upstairs washer/dryer.  The dryer vents out to the roof after a short run.  I started having trouble with my dryer.   I had a vent guy come out and he correctly diagnosed the problem as a screen on the dryer vent cap.   (I recently had a new roof and vent covers installed).   

The vent guy told me you can’t have a screen on a roof dryer vent cap.  It will catch lint and block the opening in a very short time.  My research seems to back him up.  It also makes no sense to periodically go up on the roof to clean the dryer vent.  The vent guy pulled the screen out and my dryer works fine. 

I think I need a damper/flapper on the dryer vent cap to help keep out the cold here in North Carolina?

From what I’ve read there should be a screen on the bathroom fan vent caps, but no damper/flapper.  I guess because the exit air pressure is lower?

Does this make sense?  Are there any alternative solutions?