For dryer efficiency and safety the shortest and straightest ducting route is always best.
Venting clothes dryer into roof.
Every turn increases friction loss unless you use non restrictive elbows.
When bath fans and clothes dryers vent through the roof they melt a bunch of snow.
It is not advisable to vent a dryer through the roof.
If venting outside isn t an option you can vent the dryer out of the attic through the roof using a special roof vent to keep rain out.
Venting the dryer outside in cold weather wastes a lot of heat.
Dryer vent specialists will tell you that a vertical approach to installing a dryer vent is inefficient and creates a fire risk for a home if it goes unchecked.
Doing so would fill your attic with warm moist air that could rot the framing.
The international residential code allows you to run a dryer vent through the attic but you can t terminate it there.
Air velocity reduction from friction loss promotes lint build up and makes the dryer work harder to completely dry each load.
This is one of the most common mistakes we see from people who are not experienced with air ducts.
But we don t recommend it for two reasons.
When venting dryers for long distances use rigid metal pipe with as few elbows as possible.