What should I look for in a roof dryer vent?
If you truly have significant snow accumulation then you need the following: Start with the thinnest walled 4" diameter PVC pipe you can get your hands.  Check the irrigation supply companies; Class 100, &amp; Class 125.  Terminate it about waist high directly behind where the dryer will sit, against the wall. Use 4" flexible vent material to go from the dryer to this PVC pipe.  Extend the PVC pipe through the ceiling of the laundry room and then on through the attic and through the roof line, securing along the way as necessary.  Avoid any unnecessary bends.  Using 22*bends or at the most 45*bends, off-set as necessary in the attic to avoid framing members.  I would extend through the roof about 2-feet.  Flash the pipe at the roof line with a standard 4" plumber's type rubber boot roof flashing.  Make sure it goes under the shingles. On the top of this vent pipe install a rain cap or is sometimes called a china cap. Select a cap with lots of venting space.  Eliminate any and all screen material. I like a product made by Award Metals.  They call it their 'Type B' china cap.