Cleaning lint buildup from roof vents is difficult and nesting birds and squirrels often find roof vent caps.
Dryer vent through roof or wall.
Figures a b and c show the three most common paths from the dryer to the exterior.
A roof dryer vent will require that your dryer push a gallon of water lint and hot air vertically for many feet at least 18 if you have any kind of an attic and many homes that have a roof dryer vent have 20 to 30 feet of vertical pipe.
The less back pressure is created by the roof vent the more efficiently the system performs.
Additionally squirrels and birds often nest in the roof vent caps of roof dryer vent.
Dryer vents should always be vented through the side of the house and not vented through the roof and ideally the exit should be fairly close to the ground.
Keeping a clean dryer vent is much easier when you can safely reach the exit.
Vent a dryer through the roof only as a last resort.
Use a 4 1 4 inch hole saw to cut the vent opening.
Transfer that measurement inside if necessary to mark the new dryer vent center.
The vent should exit the building through the roof or wall at least 3 feet away from any other building openings and the vent cover which must not include a screen should allow dispersal of.
These terminals need to be cleaned on a regular basis to prevent lint buildup.
Considering that back pressure higher than 6 wci is generally recognized as inefficient you can see that venting through the roof with non dryer specific vents is immediately problematic.