A normal dryer vent size is around 4 inches wide.
Dryer vent into the attic fixed.
Support the ductwork adequately to maintain this pitch don t allow the ductwork to sag in the middle.
You should then measure a small hole in the ceiling to fit the dryer vent into.
Continue the ductwork horizontally through the attic to the closest exterior wall.
If you find that it is not you can adjust it.
Pitch the attic ductwork back toward the dryer so that any condensation will run back toward the heated space.
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.
Here s what the florida building code fbc residential edition says about it.
When venting dryers for long distances use rigid metal pipe with as few elbows as possible.
Be careful you don t cut through any studs electrical wires or pipes in the process.
The international residential code allows you to run a dryer vent through the attic but you can t terminate it there.