If the dryer is an interior room of the house, vent through the attic to the roof. Note: Vent a dryer through the roof only as a last resort. Cleaning lint buildup from roof vents is difficult ...

This vent might be located low to the ground or high near the roof on the exterior ... identical to that of interior dryer vent cleaning. Snake the flexible rods through the duct and drill brush.

(CBC) "Also make sure that your ventilation is relatively short — in other words, not a long line to ventilate the dryer. Make sure that it goes through the wall, preferably directly outside ...