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.
Dryer vent into the attic fixed.
Support the ductwork adequately to maintain this pitch don t allow the ductwork to sag in the middle.
If the measurements are correct then the hole should sit 4 to 5 inches from the wall where the dryer is.
Pitch the attic ductwork back toward the dryer so that any condensation will run back toward the heated space.
A normal dryer vent size is around 4 inches wide.
Home clothes dryers don t start out venting into an enclosed space because the building code specifies that the termination of a dryer duct must be outside.
When venting dryers for long distances use rigid metal pipe with as few elbows as possible.
Here s what the florida building code fbc residential edition says about it.
If you find that it is not you can adjust it.
Continue the ductwork horizontally through the attic to the closest exterior wall.
Be careful you don t cut through any studs electrical wires or pipes in the process.